What Is Amino Acid?

In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups. In biochemistry, this shorter and more general term is frequently used to refer to alpha amino acids: those amino acids in which the amino and carboxylate functionalities are attached to the same carbon.

Amino acid residue is what is left of an amino acid once a water molecule has been lost (an H+ from the nitrogenous side and an OH- from the carboxylic side) in the formation of a peptide bond .

Amino acids are biochemical building blocks. They form short polymer chains called polypeptides or peptides which in turn form structures called proteins (see below).

Twenty amino acids are encoded by the standard genetic code and are called proteinogenic. Rarer, more complicated ones are "made to order" by the body. Proline is the only proteinogenic amino acid whose side group is cyclic and links to the a-amino group, forming a secondary amino group. Strictly speaking, this makes proline an imino acid. Other amino acids contained in proteins are usually formed by modification after translation (protein synthesis). These modifications are often essential for the function of the protein. At least two amino acids other than the standard 20 are sometimes incorporated into proteins during translation:

Selenocysteine is incorporated into some proteins at a UGA codon, which is normally a stop codon. Pyrrolysine is used by some methanogens in enzymes that they use to produce methane. It is coded for similarly to selenocysteine but with the codon UAG instead. Over 100 amino acids have been found in nature. Some of them have also been found in meteoritic material. Microorganisms and plants often produce very uncommon amino acids, which can be found in peptidic antibiotics (for example nisin or alamethicin). Lanthionine is a sulfide bridged alanine dimer which is found together with unsaturated amino acids in lantibiotics (antibiotic peptides from microbial origin). 1-Aminocyclopropane-1-carboxylic acid (ACC) is a small disubstituted cyclic amino acid and a key intermediate in the production of the plant hormone ethylene.

In addition to amino acids for protein synthesis, there are other biologically important amino acids, such as the neurotransmitters glycine, GABA and glutamate, as well as carnitine (used in lipid transport within a cell), ornithine, citrulline, homocysteine, hydroxyproline, hydroxylysine, and sarcosine.

Some of the 20 amino acids in the genetic code are called essential amino acids, because they cannot be synthesized by the body from other compounds through chemical reactions, but instead must be taken in with food. In humans, the essential amino acids are lysine, leucine, isoleucine, methionine, phenylalanine, threonine, tryptophan, valine, and (in children) histidine and arginine.

Uses of amino acids Monosodium glutamate is a food additive to enhance flavor. L-DOPA (L-dihydroxyphenylalanine) is a drug used to treat Parkinsonism. 5-HTP (5-hydroxytryptophan) has been used to treat neurological problems associated with PKU (phenylketonuria).

Amino Acids, important class of organic compounds that contain both the amino (8NH2) and carboxyl (8COOH) groups. Of these acids, 20 serve as the building blocks of proteins. Known as the standard, or alpha, amino acids, they comprise alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine.

The amino and carboxyl groups are both attached to a single carbon atom, which is called the alpha carbon atom. Attached to the carbon atom is a variable group (R); it is in their R groups that the molecules of the 20 standard amino acids differ from one another. In the simplest of the acids, glycine, the R consists of a single hydrogen atom. Other amino acids have more complex R groups that contain carbon as well as hydrogen and may include oxygen, nitrogen, or sulphur, as well.

When a living cell makes protein, the carboxyl group of one amino acid reacts with the amino group of another to form a peptide bond. The carboxyl group of the second amino acid similarly reacts with the amino group of a third, and so on, until a long chain is produced. This chainlike molecule, which may contain from 50 to several hundred amino acid subunits, is called a polypeptide. A protein may be formed of a single polypeptide chain, or it may consist of several such chains held together by weak molecular bonds. Each protein is formed according to a precise set of instructions contained within the nucleic acid—the genetic material of the cell. These instructions determine which of the 20 standard amino acids are to be incorporated into the protein, and in what sequence. The R groups of the amino acid subunits determine the final shape of the protein and its chemical properties; an extraordinary variety of proteins can be produced from the same 20 subunits.

The standard amino acids serve as raw materials for the manufacture of many other cellular products, including hormones and pigments. In addition, several of these amino acids are key intermediates in cellular metabolism.

Most plants and micro-organisms are able to use inorganic compounds to make all the amino acids they require for normal growth. Animals, however, must obtain some of the standard amino acids from their diet in order to survive; these particular amino acids are called essential. Essential amino acids for humans include lysine, tryptophan, valine, histidine, leucine, isoleucine, phenylalanine, threonine, methionine, and arginine. They are found in adequate amounts in protein-rich foods from animal sources or in carefully chosen combinations of plant proteins.

In addition to the amino acids that form proteins, more than 150 other amino acids have been found in nature, including some that have the carboxyl and amino groups attached to separate carbon atoms. These unusually structured amino acids are most often found in fungi and higher plants.

Amino acids are the basic structural units of proteins and, like chocolates, come in many different “flavours”. Each is made to the same design, with an amino group, a carboxyl group, a hydrogen atom, and a distinct R group (or side chain) all of which are bonded to an a-carbon atom. Amino acids are linked together in proteins by a peptide bond, made by the reaction of the carboxyl group of one amino acid with the amino group of the next.

Twenty kinds of side chains varying in size, shape, charge, bonding capacity, and chemical reactivity are commonly found in proteins. Indeed, all proteins in all species from bacteria to humans are constructed from the same set of 20 amino acids. This fundamental “alphabet” of proteins is at least two billion years old, the remarkable range of functions mediated by proteins resulting from the chemical diversity of these 20 kinds of building blocks. We will see below how this alphabet is used to create the intricate three-dimensional structures that enable proteins to carry out so many biological processes.

The amino acid side chains (the part that projects from the polypeptide chain) range in size from a single hydrogen (in glycine) to a large, nitrogen-containing aromatic ring (in tryptophan). Five of the amino acids have side chains that can form ions in solution and can thereby carry a charge. The others are uncharged, and may be water-loving or water-hating, acidic or alkaline. The sequence in which amino acids are linked together determines the way in which the polypeptide chain folds up, and hence the three-dimensional structure of the protein. In broad terms, the chemistry of the amino acid side chains, especially those exposed on the protein's surface, specify its interactions with other molecules and hence the protein's function in the cell.

In chemistry, especially in organic chemistry and biochemistry, an amino group is an ammonia-like functional group.

-NH2 A compound containing an amino group is called an amine.

In chemistry, carboxylic acids (also called alkanoic acids) are organic acids characterized by the presence of a carboxyl group.

Carboxylic acids are typically weak acids, with only about 1% of RCOOH molecules dissociated into H+ cation and RCOO- anions at room temperature in aqueous solution. The anion RCOO- is usually named with the suffix "-ate", so acetic acid, for example, becomes acetate ion.

The two electronegative oxygen atoms tend to pull the electron away from the hydrogen of the hydroxyl group, and the remaining proton H+ can more easily leave. The remaining negative charge is then distributed symmetrically among the two oxygen atoms, and the two carbon–oxygen bonds take on a partial double bond character (i.e., they are delocalised).

This is a result of the resonance structure created by the carbonyl component of the carboxylic acid, without which the OH group does not as easily lose its H+ (see alcohol).

The presence of electronegative groups (such as -OH or -Cl) next to the carboxylic group increases the acidity. So for example, trichloroacetic acid (three -Cl groups) is a stronger acid than lactic acid (one -OH group) which in turn is stronger than acetic acid (no helping group).

Reactions Carboxylic acids can be made by the complete oxidation of primary alcohols.

Carboxylic acids react with bases to form carboxylate salts, in which the hydrogen of the -OH group is replaced with a metal ion. Thus, ethanoic acid (the same as acetic acid) reacts with sodium bicarbonate (baking soda) to form sodium ethanoate (sodium acetate), carbon dioxide, and wate.  Carboxyl groups also react with amine groups to form peptide bonds and with alcohols to form esters.

Carboxylic acids can be reduced by LiAlH4 to form primary alcohols.

A peptide bond is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water (H2O). This is a dehydration synthesis reaction, and usually occurs between amino acids.

The resulting C-N bond is called a peptide bond, and the resulting molecule is called an amide. Polypeptides and proteins are chains of amino acids held together by peptide bonds. The backbone of PNA is also held together by peptide bonds.

The C-N bond has a partial double bond character (with the Nitrogen atom attaining a partial positive charge and the oxygen atom a partial negative charge) and the molecule can normally not rotate around this bond. The whole arrangement of the four C,O,N,H atoms as well as the two attached carbons in a peptide bond is planar.

A peptide bond can be broken by amide hydrolysis (the adding of water). The peptide bonds in proteins are metastable, meaning that in the presence of water they will break spontaneously, releasing about 10 kJ/mol of free energy, but this process is extremely slow. In living organisms, the process is facilitated by enzymes. Living organisms also employ enzymes to form peptide bonds; this process requires free energy. The wavelength of absorbance for a peptide bond is 220-280nm.

Peptides are the family of molecules formed from the linking, in a defined order, of various amino acids. The link between one amino acid residue and the next is an amide bond, and is sometimes referred to as a peptide bond. An amide bond is somewhat shorter than a typical carbon-nitrogen single bond, and has a partial double-bond character, because the participating carbon molecule is doubly bonded to an oxygen molecule and the nitrogen has a lone pair of electrons available for bonding.

Peptides (like proteins) occur in nature and are responsible for a wide array of functions, many of which are not yet understood. Antimicrobial peptides generally disrupt the membranes of a target cell, causing lysis of the cell. How this occurs, and what determines the activity and selectivity of these peptides, is currently only known approximately.

Peptides differ from proteins, which are also long chains of amino acids, by virtue of their size. Traditionally, those peptide chains that are short enough to make synthetically from the constituent amino acids are called peptides rather than proteins. The dividing line is at approximately 50 amino acids in length, since naturally-occurring proteins tend, at their smallest, to be hundreds of residues long. So, in essence, a peptide is a small protein.

Peptidomimetics (such as peptoids and β-peptides) are molecules related to peptides, but with different properties.

The twenty amino acids that are coded in the standard genetic code are called proteinogenic (protein building).

Some of the 20 amino acids in the genetic code are called essential amino acids, because they cannot be synthesized by the body from other compounds through chemical reactions, but instead must be taken in with food. In humans, the essential amino acids are lysine, leucine, isoleucine, methionine, phenylalanine, threonine, tryptophan, valine, and (in children) histidine and arginine.

Proline is the only cyclic proteinogenic amino acid.

First, what is an amino acid? Amino Acids are chemical substances that make up protein. There are 20 amino acids, of those there are 8 essential amino acids. An essential amino acid is one that cannot be synthesized from other available resources, and therefore must be supplied as part of the diet. Not all amino acids need to be supplied. Alanine can be synthesized from pyruvate in humans, but humans cannot synthesize phenylalanine and hence it is an essential amino acid.

The boundary between an essential amino acid and one that is not can sometimes be unclear. Methionine and homocysteine, sulfur-containing amino acids, can be converted into each other, but neither can be synthesized from scratch in humans. Cysteine can be made from homocysteine, but it cannot be synthesized from scratch either. So, for convenience, people will sometimes count the sulfur-containing amino acids as a single pool. Likewise, because of the urea cycle, arginine, ornithine, and citrulline are interconvertible, and therefore form a single pool of nutritionally-equivalent amino acids.

Foodstuffs that are lacking essential amino acids are poor sources of protein equivalents, as the body will tend to deaminate the amino acids obtained and convert proteins into fats and carbohydrates instead. Therefore, a balance of essential amino acids is necessary for a high degree of net protein utilization, which is the mass ratio of amino acids converted to proteins to amino acids supplied. This figure is somewhat affected by salvage of essential amino acids in the body, but otherwise is profoundly affected by the limiting amino acid content, which is the essential amino acid found in the smallest quantity in the foodstuff.

It is therefore a good idea to mix foodstuffs that have different weaknesses in their essential amino acid distributions. This limits the loss of nitrogen through deamination and increases overall net protein utilization.

8 amino acids are generally regarded as essential, with two others, histidine and arginine, essential only in children:

tryptophan lysine methionine phenylalanine threonine valine leucine isoleucine

The question of which amino acids are essential varies from species to species, as different metabolisms are able (or unable) to synthesize different substances. For instance, taurine (which is not, by strict definition, an amino acid) is essential for the cat, but not for the dog; thus, taurine is added to commercial cat food, but not to dog food - and therefore, dog food is not nutritionally sufficient for cats.

Isoleucine is one of the 20 most common natural amino acids, and coded for in DNA. Its chemical composition is identical to that of leucine, but the arrangement of its atoms is slightly different resulting in different properties. Nutritionally, in humans, isoleucine is an essential amino acid.

Leucine is one of the 20 most common amino acids on Earth, and coded for by DNA. Its chemical composition is identical to that of isoleucine, but its atoms are arranged differently resulting in different properties. Nutritionally, in humans, leucine is an essential amino acid.

Valine is one of the 20 most common natural amino acids on Earth, and is coded for in DNA. Nutritionally, valine is also an essential amino acid.

In Sickle Cell Anaemia, it subsitutes for the hydrophilic glutamic acid amino acid in haemoglobin, and because it is hydrophobic, the haemoglobin does not fold correctly.

Valine is uncharged overall, as its R group is neutral, and the charges from its amino and carboxylic acid groups balance out- a zwitterion

Threonine is one of the 20 most common natural amino acids on Earth. Nutritionally, in humans, threonine is also an essential amino acid.

The threonine side chain can undergo O-linked glycosylation.

The amino acid Phenylalanine exists in two forms, the D- and L- forms. It has a phenyl side chain. L-Phenylalanine(LPA, C9H12NO2) is an electrically neutral amino acid found in proteins, coded for by DNA. Its mirror image, D-phenylalanine (DPA), can be synthesized artificially.

L-phenylalanine is used in the human body, where it is an essential amino acid. L-Phenylalanine can also be converted into tyrosine. Tyrosine is converted into L-DOPA, norepinephrine, and epinephrine. D-phenylalanine can only be converted into phenylethylamine.

The genetic disorder phenylketonuria is an inability to metabolize phenylalanine.

The synthesized mix DL-Phenylalanine (DLPA), which is a combination of the D- and L- forms, is used as a nutritional supplement.

Phenylalanine is part of the composition of aspartame, a common sweetener found in prepared foods (particularly soft drinks, and gum). Due to phenylketonuria, products containing aspartame usually have a warning label that they contain phenylalanine, in compliance with U.S. FDA guidelines.

The genetic code for phenylanaline was the first codon discovered. Marshall W. Nirenberg discovered that when he inserted RNA made up of multiple uracil repeats into E. coli, the bacterium produced a new protein, made up solely of repeated phenylalanine amino acids.

Methionine (Met, M. C5H11NO2S) is a essential nonpolar amino acid, and a lipotropic.

It and cysteine are the only sulfur containing amino acids that are coded for by DNA (Homocysteine is an amino acid and contains sulfur, but is a product of S-adenosylmethionine 1 carbon metabolism and is not coded for by DNA). Methionine is a methyl donor as S-adenosyl methionine (SAM). It is incorporated into the N-terminal position of all proteins in eukaryotes and archaea, though it may be removed by post-translational modification (bacteria incorporate N-formyl methionine instead). Methionine can also occur at other positions in the protein. It plays a role in cysteine, carnitine and taurine synthesis by the transsulfuration pathway, lecithin production, the synthesis of phosphatidylcholine and other phospholipids. Improper conversion of methionine can lead to atherosclerosis. Methionine is a chelating agent.

Methionine is one of only two amino acids encoded by just one codon (AUG) in the standard genetic code (tryptophan, encoded by UGG, is the other).

Lysine is one of the 20 most common natural amino acids on Earth. Lysine is directly coded for in DNA and molecular biologists tend to abbreviate it to Lys or K. Nutritionally, in humans, lysine is an essential amino acid. Lysine can be used as a nutritional supplement to help against herpes.

Lysine is the limiting amino acid in all cereal grains, but is plentiful in all pulses. A deficiency in Lysine can result in a deficiency in niacin (which is a B Vitamin). This can cause the disease pellagra. Plants that contain significant amounts of lysine include:

Buffalo Gourd (10,130–33,000 ppm) in Seed Berro, Watercress (1,340–26,800 ppm) in Herb. Soybean (24,290–26,560 ppm) in Seed. Carob, Locust Bean, St.John's-Bread (26,320 ppm) in Seed; Black Bean, Dwarf Bean, Field Bean, Flageolet Bean, French Bean, Garden Bean, Green Bean, Haricot, Haricot Bean, Haricot Vert, Kidney Bean, Navy Bean, Pop Bean, Popping Bean, Snap Bean, String Bean, Wax Bean (2,390–25,700 ppm) in Sprout Seedling; Ben Nut, Benzolive Tree, Drumstick Tree, Horseradish Tree, Jacinto (Sp.), Moringa, West Indian Ben (5,370–25,165 ppm) in Shoot. Lentil (7,120–23,735 ppm) in Sprout Seedling. Asparagus Pea, Goa Bean, Winged Bean (21,360–23,304 ppm) in Seed. Lambsquarter (3,540–22,550 ppm) in Seed. Lentil (19,570–22,035 ppm) in Seed. White Lupine (19,330–21,585 ppm) in Seed. Black Caraway, Black Cumin, Fennel-Flower, Nutmeg-Flower, Roman Coriander (16,200–20,700 ppm) in Seed. Spinach (1,740–20,664 ppm) in Plant. Amaranth, Quinoa

Tryptophan is an amino acid and essential in human nutrition. It is one of the 20 amino acids in the genetic code (codon UGG), and its symbol is Trp or W.

Molecular formula: C11H12N2O2 Molecular weight: 204.23 Isoelectric point: pH 5.89 CAS number: 73-22-3 Tryptophan is also a precursor for serotonin (a neurotransmitter) and melatonin (a neurohormone). The functional group of tryptophan is indole, see that article for more on its chemical properties.

For some time, tryptophan was available in health food stores as a dietary supplement. Many people found tryptophan to be a safe and reasonably effective sleep aid, probably due to its ability to increase brain levels of serotonin (a calming neurotransmitter when present in moderate levels) and/or melatonin (a drowsiness-inducing hormone secreted by the pineal gland in response to darkness or low light levels). Clinical research tended to confirm tryptophan's effectiveness as a natural sleeping pill and for a growing variety of other conditions typically associated with low serotonin levels or activity in the brain. In particular, tryptophan showed considerable promise as an antidepressant, alone and as an "augmentor" of antidepressant drugs. Other promising indications included relief of chronic pain and reduction of impulsive, violent, manic, addictive, obsessive, or compulsive behaviours and disorders.

In 1989, a large outbreak of a mysterious, disabling, and in some cases deadly autoimmune illness called eosinophilia-myalgia syndrome was traced to an improperly prepared batch of tryptophan. The bacterial culture used to synthesise tryptophan by a major Japanese manufacturer had recently been genetically engineered to increase tryptophan production: unfortunately, with the higher tryptophan concentration in the culture medium, the purification process had also been streamlined to reduce costs, and a purification step that used charcoal absorption to remove impurities had been omitted. This allowed another bacterial metabolite through the purification, and this contaminant of the end-product had been responsible for the toxic effects. Regardless of the origin of the toxicity, tryptophan was banned from sale in the US, and other countries followed suit.

Though tryptophan supplements are still banned from over-the-counter sale, properly produced pharmaceutical-grade tryptophan continues to be used legally as an essential nutrient in infant formulas and intravenous feeding and, in recent years, compounding pharmacies and some mail-order supplement retailers have begun selling tryptophan to the general public. Tryptophan has also remained on the market as a presciption drug (Tryptan) which some psychiatrists continue to prescribe, particularly as an augmenting agent for people who are unresponsive to antidepressant drugs. Indeed, tryptophan has continued to be used in clinical and experimental studies employing human patients and subjects. Several of these studies suggest tryptophan can effectively treat the fall/winter depression variant of seasonal affective disorder (SAD).

Dietary sources: tryptophan is particularly plentiful in chocolate, oats, bananas, dried dates, milk, cottage cheese, meat, fish, turkey, and peanuts. While tryptophan is associated with serotonin and melatonin production, contrary to common belief most experts do not think it contributes much to the drowsiness experienced by many diners after a large turkey-laden meal, such as North American Thanksgiving dinner. The digestive demand of excessive carbohydrates is the primary culprit, with alcohol often contributing. As a soporific, tryptophan from food works effectively only on an empty stomach, and even then it's difficult to get enough to be effective.

Arginine is one of the 20 most common natural amino acids. Is has guanidino side chain functional group. In non-hepatic tissues, arginine can be biosynthesized by the ornithine cycle (or urea cycle). Even so, arginine is often classed as one of the 10 essential amino acids. This need evidently is restricted to children.

Arginine can be decarboxylated, yielding agmatine. Conversion by nitric oxide synthase to citrulline also yields the vasoactive mediator nitric oxide.

Histidine is one of the 20 most common natural amino acids, coded for in DNA. Nutritionally, in humans, histidine is considered an essential amino acid, but mostly only in children. The imidazole side chains of histidine and the relatively neutral pK (ca 6.0) mean that relatively small shifts in cellular pH will change its charge. For this reason, this amino acid side chain finds its way into considerable use as a co-ordinating ligand in metalloproteins, and also as a catalytic site in certain enzymes. The imidazole side chain has two nitrogens with different properties, one is bound to hydrogen and donates its lone pair to the aromatic ring and as such is slighty acidic, while the other one donates only one electron to the ring so it has a free lone pair and is basic. These properties are exploited in different ways in proteins. In catalytic triads, the basic nitrogen of histidine is used to abstract a proton from serine, threonine or cysteine to activate it as a nucleophile. In a histidine proton shuttle, histidine is used to quickly shuttle protons, it can do this by abstracting a proton with its basic nitrogen to make a positively charged intermediate and then use another molecule, a buffer, to extract the proton from its acidic nitrogen. In carbonic anhydrases, a histidine proton shuttle is utilized to rapidly shuttle protons away from a zinc-bound water molecule to quickly regenerate the active form of the enzyme.

The amino acid is a precursor for histamine biosynthesis.

Histamine is a monoamine chemical involved in local immune responses.

Cysteine is a naturally occurring hydrophilic ("water loving") amino acid which has a sulfhydryl (SH) group and is found in most proteins. When it is exposed to air it oxidizes to form cystine, which is two cysteine molecules joined by a disulfide bond. One molecule of water (H2O) is the byproduct from the creation of each molecule of cystine. It can be taken as a supplement in the form of N-acetylcysteine (NAC).

Threonine is one of the 20 most common natural amino acids on Earth. Nutritionally, in humans, threonine is also an essential amino acid.

The threonine side chain can undergo O-linked glycosylation.

Ornithine is one of the products of the action of the enzyme arginase on L-arginine, creating urea. Therefore, ornithine is a central part of the urea cycle, which allows for the disposal of excess nitrogen.

Ornithine is not an amino acid coded for by DNA, and in that sense, is not involved in protein synthesis. However, in mammalian non-hepatic tissues, the main use of the urea cycle is in arginine biosynthesis, so as an intermediate in metabolic processes, ornithine is quite important.

Ornithine, via the action of ornithine decarboxylase (E.C. 4.1.1.17), is the starting point for the synthesis of polyamines such as putrescine.

In bacteria, such as E. coli, ornithine can be synthesized from L-glutamate (see reference below).

L-citrulline is made from L-ornithine and carbamoyl phosphate in one of the central reactions in the urea cycle. It is also produced from L-arginine as a by-product of the reaction catalyzed by the enzyme NO synthase. L-citrulline, while being an amino acid, is not involved in protein synthesis and is not one of the amino acids coded for by DNA.

Alanine is one of the 20 most common natural amino acids. It is hydrophobic, with a methyl group side chain, and is the second-smallest of the 20 after glycine. Alanine is a non-essential amino acid and was first isolated in 1879.

L-Alanine is created in muscle cells from glutamate in a process called transamination. In the liver, alanine is transformed into pyruvate. Further, alanine aminotransferase catalyzes the reaction by which the amino group of alanine is transferred to α-ketoglutarate.

AMINO ACIDS are the "building Blocks" of the body. Besides building cells and repairing tissue, they form antibodies to combat invading bacteria & viruses; they are part of the enzyme & hormonal system; they build nucleoproteins (RNA & DNA); they carry oxygen throughout the body and participate in muscle activity. When protein is broken down by digestion the result is 22 known amino acids. Eight are essential (cannot be manufactured by the body) the rest are non-essential ( can be manufactured by the body with proper nutrition).

TRYPTOPHAN (Essential Amino Acid) A natural relaxant, helps alleviate insomnia by inducing normal sleep; reduces anxiety & depression; helps in the treatment of migraine headaches; helps the immune system; helps reduce the risk of artery & heart spasms; works with Lysine in reducing cholesterol levels.

LYSINE (Essential Amino Acid) Insures the adequate absorption of calcium; helps form collagen ( which makes up bone cartilage & connective tissues); aids in the production of antibodies, hormones & enzymes. Recent studies have shown that Lysine may be effective against herpes by improving the balance of nutrients that reduce viral growth. A deficiency may result in tiredness, inability to concentrate, irritability, bloodshot eyes, retarded growth, hair loss ,anemia & reproductive problems.

METHIONINE (Essential Amino Acid) Is a principle supplier of sulfur which prevents disorders of the hair, skin and nails; helps lower cholesterol levels by increasing the liver's production of lecithin; reduces liver fat and protects the kidneys; a natural chelating agent for heavy metals; regulates the formation of ammonia and creates ammonia-free urine which reduces bladder irritation; influences hair follicles and promotes hair growth.

PHENYLALAINE (Essential Amino Acid) Used by the brain to produce Norepinephrine, a chemical that transmits signals between nerve cells and the brain; keeps you awake & alert; reduces hunger pains; functions as an antidepressant and helps improve memory.

THREONINE (Essential Amino Acid) Is an important constituent of collagen, Elastin, and enamel protein; helps prevents fat build-up in the liver; helps the digestive and intestinal tracts function more smoothly; assists metabolism and assimilation.

VALINE (Essential Amino Acid) Promotes mental vigor, muscle coordination and calm emotions.

LEUCINE & ISOLEUCINE (Essential Amino Acid) They provide ingredients for the manufacturing of other essential biochemical components in the body, some of which are utilized for the production of energy, stimulants to the upper brain and helping you to be more alert.

ARGININE (Non-Essential Amino Acid) Studies have shown that is has improved immune responses to bacteria, viruses & tumor cells; promotes wound healing and regeneration of the liver; causes the release of growth hormones; considered crucial for optimal muscle growth and tissue repair.

TYROSINE (Non-Essential Amino Acid) Transmits nerve impulses to the brain; helps overcome depression; Improves memory; increases mental alertness; promotes the healthy functioning of the thyroid, adrenal and pituitary glands.

GLYCINE (Non-Essential Amino Acid) Helps trigger the release of oxygen to the energy requiring cell-making process; Important in the manufacturing of hormones responsible for a strong immune system.

SERINE (Non-Essential Amino Acid) A storage source of glucose by the liver and muscles; helps strengthen the immune system by providing antibodies; synthesizes fatty acid sheath around nerve fibers.

GLUTAMIC ACID (Non-Essential Amino Acid) Considered to be nature's "Brain food" by improving mental capacities; helps speed the healing of ulcers; gives a "lift" from fatigue; helps control alcoholism, schizophrenia and the craving for sugar.

ASPARTIC ACID (Non-Essential Amino Acid) Aids in the expulsion of harmful ammonia from the body. When ammonia enters the circulatory system it acts as a highly toxic substance which can be harmful to the central nervous system. Recent studies have shown that Aspartic Acid may increase resistance to fatigue and increase endurance.

TAURINE (Non-Essential Amino Acid) Helps stabilize the excitability of membranes which is very important in the control of epileptic seizures. Taurine and sulfur are considered to be factors necessary for the control of many biochemical changes that take place in the aging process; aids in the clearing of free radical wastes.

CYSTINE (Non-Essential Amino Acid) Functions as an antioxidant and is a powerful aid to the body in protecting against radiation and pollution. It can help slow down the aging process, deactivate free radicals, neutralize toxins; aids in protein synthesis and presents cellular change. It is necessary for the formation of the skin, which aids in the recovery from burns and surgical operations. Hair and skin are made up 10-14% Cystine.

HISTIDINE (Non-Essential Amino Acid) Is found abundantly in hemoglobin; has been used in the treatment of rheumatoid arthritis, allergic diseases, ulcers & anemia. A deficiency can cause poor hearing.

PROLINE (Non-Essential Amino Acid) Is extremely important for the proper functioning of joints and tendons; also helps maintain and strengthen heart muscles.

ALANINE (Non-Essential Amino Acid) Is an important source of energy for muscle tissue, the brain and central nervous system; strengthens the immune system by producing antibodies; helps in the metabolism of sugars and organic acids.

Chemical Nature of the Amino Acids

All peptides and polypeptides are polymers of alpha-amino acids. There are 20 a-amino acids that are relevant to the make-up of mammalian proteins (see below). Several other amino acids are found in the body free or in combined states (i.e. not associated with peptides or proteins). These non-protein associated amino acids perform specialized functions. Several of the amino acids found in proteins also serve functions distinct from the formation of peptides and proteins, e.g., tyrosine in the formation of thyroid hormones or glutamate acting as a neurotransmitter. The a-amino acids in peptides and proteins (excluding proline) consist of a carboxylic acid (-COOH) and an amino (-NH2) functional group attached to the same tetrahedral carbon atom. This carbon is the a-carbon. Distinct R-groups, that distinguish one amino acid from another, also are attached to the alpha-carbon (except in the case of glycine where the R-group is hydrogen). The fourth substitution on the tetrahedral a-carbon of amino acids is hydrogen.

Amino Acid Classifications

Each of the 20 a-amino acids found in proteins can be distinguished by the R-group substitution on the a-carbon atom. There are two broad classes of amino acids based upon whether the R-group is hydrophobic or hydrophilic. The hydrophobic amino acids tend to repel the aqueous environment and, therefore, reside predominantly in the interior of proteins. This class of amino acids does not ionize nor participate in the formation of H-bonds. The hydrophilic amino acids tend to interact with the aqeuous environment, are often involved in the formation of H-bonds and are predominantly found on the exterior surfaces proteins or in the reactive centers of enzymes.

What do Amino Acids Do? In the human body, amino acids not only form the building blocks of our voluntary, or skeletal, muscle tissue, such as the biceps, quadriceps, etc., but they also form the building blocks of our less ego oriented involuntary muscles, such as the heart. In addition to this muscle building function, each individual amino acid has a specific function in the body. These functions include among others in; assisting in transporting long chain triglycerides, or dietary fat, into the cells for energy; stimulating the pituitary to secrete growth hormone, which is involved in developing lean muscle tissue as well as mobilizing fatty acids from the adipose tissue (i.e., dropping bodyfat); supplying the body with nitrogen; and much, much, more. Who Should Take Amino Acids? From the previous discussion we can see that an obvious source of amino acids is from the dietary intake of protein. However, as we will now see there are some reasons that this source may not always be the most desirable. First, a quick look down the nutrition charts will reveal that foods that are high in protein tend to, also, be high in fat. Second, as we age our level of digestive enzymes tends to decrease, thus impairing our ability to efficiently utilize proteins. At best, our digestive systems are extremely inefficient. e, i, e, l, e. Third, for the athlete, meals that present an incomplete amino acid profile (i.e., a shortage of the essential amino acids) to our system will be of marginal use to the muscle building process. Therefore, a well balanced amino acid supplement can prove to be extremely cost effective for individuals desiring to maximize their protein intake at a minimal caloric cost.

Acid-Base Properties of the Amino Acids

The a-COOH and a-NH2 groups in amino acids are capable of ionizing (as are the acidic and basic R-groups of the amino acids). As a result of their ionizability the following ionic equilibrium reactions may be written:

R-COOH <--------> R-COO- + H+

R-NH3+ <---------> R-NH2 + H+

The equilibrium reactions, as written, demonstrate that amino acids contain at least two weakly acidic groups. However, the carboxyl group is a far stronger acid than the amino group. At physiological pH (around 7.4) the carboxyl group will be unprotonated and the amino group will be protonated. An amino acid with no ionizable R-group would be electrically neutral at this pH. This species is termed a zwitterion. Like typical organic acids, the acidic strength of the carboxyl, amino and ionizable R-groups in amino acids can be defined by the association constant, Ka or more commonly the negative logrithm of Ka, the pKa. The net charge (the algebraic sum of all the charged groups present) of any amino acid, peptide or protein, will depend upon the pH of the surrounding aqueous environment. As the pH of a solution of an amino acid or protein changes so too does the net charge. This phenomenon can be observed during the titration of any amino acid or protein. When the net charge of an amino acid or protein is zero the pH will be equivalent to the isoelectric point: pI.

Functional Significance of Amino Acid R-Groups

In solution it is the nature of the amino acid R-groups that dictate structure-function relationships of peptides and proteins. The hydrophobic amino acids will generally be encountered in the interior of proteins shielded from direct contact with water. Conversely, the hydrophilic amino acids are generally found on the exterior of proteins as well as in the active centers of enzymatically active proteins. Indeed, it is the very nature of certain amino acid R-groups that allow enzyme reactions to occur. The imidazole ring of histidine allows it to act as either a proton donor or acceptor at physiological pH. Hence, it is frequently found in the reactive center of enzymes. Equally important is the ability of histidines in hemoglobin to buffer the H+ ions from carbonic acid ionization in red blood cells. It is this property of hemoglobin that allows it to exchange O2 and CO2 at the tissues or lungs, respectively. The primary alcohol of serine and threonine as well as the thiol (-SH) of cysteine allow these amino acids to act as nucleophiles during enzymatic catalysis. Additionally, the thiol of cysteine is able to form a disulfide bond with other cysteines:

Cysteine-SH + HS-Cysteine <--------> Cysteine-S-S-Cysteine

This simple disulfide is identified as cystine. The formation of disulfide bonds between cysteines present within proteins is important to the formation of active structural domains in a large number of proteins. Disulfide bonding between cysteines in different polypeptide chains of oligomeric proteins plays a crucial role in ordering the structure of complex proteins, e.g. the insulin receptor.

Optical Properties of the Amino Acids

A tetrahedral carbon atom with 4 distinct constituents is said to be chiral. The one amino acid not exhibiting chirality is glycine since its '"R-group" is a hydrogen atom. Chirality describes the handedness of a molecule that is observable by the ability of a molecule to rotate the plane of polarized light either to the right (dextrorotatory) or to the left (levorotatory). All of the amino acids in proteins exhibit the same absolute steric configuration as L-glyceraldehyde. Therefore, they are all L-a-amino acids. D-amino acids are never found in proteins, although they exist in nature. D-amino acids are often found in polypetide antibiotics. The aromatic R-groups in amino acids absorb ultraviolet light with an absorbance maximum in the range of 280nm. The ability of proteins to absorb ultraviolet light is predominantly due to the presence of the tryptophan which strongly absorbs ultraviolet light.

The Peptide Bond

Peptide bond formation is a condensation reaction leading to the polymerization of amino acids into peptides and proteins. Peptides are small consisting of few amino acids. A number of hormones and neurotransmitters are peptides. Additionally, several antibiotics and antitumor agents are peptides. Proteins are polypeptides of greatly divergent length. The simplest peptide, a dipeptide, contains a single peptide bond formed by the condensation of the carboxyl group of one amino acid with the amino group of the second with the concomitant elimination of water. The presence of the carbonyl group in a peptide bond allows electron resonance stabilization to occur such that the peptide bond exhibits rigidity not unlike the typical -C=C- double bond. The peptide bond is, therefore, said to have partial double-bond character.

There are 20 naturally occuring amino acids that make up proteins. The basic chemical structural units of proteins are amino acids. With the exception of proline, amino acids have a common structure. The structure consists of a central carbon atom (the alpha carbon), to which is bonded to a amino acid (-NH2), a carboxyl group (-COOH), and a hydrogen atom. Amino acids in solution at isoelectric pH are mainly dipolar ions. This is generally how amino acids exist at cellular pH. The amino group (-NH2) accepts a proton and becomes (-NH3+), and the carboxyl group (-COOH) donates a proton and becomes dissociated (-COO-). Because of their amino and carboxyl groups, proteins in solution resist changes in acidity and alkalinity and so are important biological buffers.

The 20 amino acids are classified into subgroups, based on whether the R group is acidic, basic, neutral-polar, or neutral-nonpolar. Bound to the central carbon atom, each amino acid has an additional chemical group, called the R group. The R group varies from one amino acid to another; and, also gives each amino acid its distinctive properties. It is the organization of the R-group that gives a protein its structural and functional properties.

Amino acids with nonpolar R groups(also known as side chains) are classified as hydrophobic, whereas, those with polar side chains are classified as hydrophilic. Acidic amino acids have side chains that contain a carboxyl group. At cellular pH the carboxyl group is dissociated so that the R group has a negative charge. Basic amino acids are positively charged as a result of the dissociation of the amino group in their side chains. Acidic and basic chains ar ionic and therefore hydrophobic.

Amino acids play central roles both as building blocks of proteins and as intermediates in metabolism. The 20 amino acids that are found within proteins convey a vast array of chemical versatility. The precise amino acid content, and the sequence of those amino acids, of a specific protein, is determined by the sequence of the bases in the gene that encodes that protein. The chemical properties of the amino acids of proteins determine the biological activity of the protein. Proteins not only catalyze all (or most) of the reactions in living cells, they control virtually all cellular process. In addition, proteins contain within their amino acid sequences the necessary information to determine how that protein will fold into a three dimensional structure, and the stability of the resulting structure. The field of protein folding and stability has been a critically important area of research for years, and remains today one of the great unsolved mysteries. It is, however, being actively investigated, and progress is being made every day.

As we learn about amino acids, it is important to keep in mind that one of the more important reasons to understand amino acid structure and properties is to be able to understand protein structure and properties. We will see that the vastly complex characteristics of even a small, relatively simple, protein are a composite of the properties of the amino acids which comprise the protein.

Essential amino acids Humans can produce 10 of the 20 amino acids. The others must be supplied in the food. Failure to obtain enough of even 1 of the 10 essential amino acids, those that we cannot make, results in degradation of the body's proteins—muscle and so forth—to obtain the one amino acid that is needed. Unlike fat and starch, the human body does not store excess amino acids for later use—the amino acids must be in the food every day.

The 10 amino acids that we can produce are alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine and tyrosine. Tyrosine is produced from phenylalanine, so if the diet is deficient in phenylalanine, tyrosine will be required as well. The essential amino acids are arginine (required for the young, but not for adults), histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. These amino acids are required in the diet. Plants, of course, must be able to make all the amino acids. Humans, on the other hand, do not have all the the enzymes required for the biosynthesis of all of the amino acids.

The 23 or so amino acids are the molecular building blocks of proteins. According to one accepted classification, 9 are termed indispensable amino acids (IAA, sometimes called essential), meaning that they must be supplied from some food or supplement source; the others, which used to be classified simply as nonessential, are now more correctly termed dispensable amino acids (DAA) or conditionally indispensable, based on the body's ability to synthesize them from other amino acids.

You may not give it much thought when you sink your teeth into a chicken breast (or lentil stew), but the content and balance of amino acids, particularly the ratio of IAA to DAA, is what determines the body and health building value of a protein food or supplement. But that isn't all that matters.

When to Take Amino Acids? It must be kept in mind that the timing, as well as the presence of certain co-factors, such as vitamins and minerals, are essential to the success of these programs. By understanding the processes that ultimately lead these building blocks to the muscle cells it is possible to optimize their usage. At the Center we always recommend that amino acids (with the exception of specific free form combinations, i.e, GH releasers) should be taken with meals. The reason for this is three fold. First, we are not chickens. We do not deal well with swallowing hard masses. The meal serves as a buffering, or softening, agent for the aminos. Second, if we eat a meal that has an incomplete amino acid profile then the muscle building benefits will be considerably reduced. A quality amino acid supplement can help us to "get more" from our meals. Third, the transport of amino acids from the bloodstream into the muscle cells appears to be regulated by the hormone, insulin. Due to the fact that our meals traditionally have some carbohydrate value, the corresponding insulin release will facilitate the increased utilization of the amino acids. g, l, d, j, c. The prior reasoning combined with considerable clinical experience has led us to utilize this administration approach that, while flying in the face of traditional "gym wisdom", has led us to produce a considerable number of world class athletes.

In addition to being influenced by the carbohydrates, fats and total calories associated with it, protein quality is related to the amount of the specific aminos within both the IAA and DAA categories (for example, the amount of glutamine and branched chain amino acids, or BCAAs - leucine, isoleucine and valine). While the amount of IAAs are generally of greater importance, the DAAs are also significant because they're synthesized too slowly to support maximum growth. Even if a source has a perfect amino acid profile for a given individual and lifestyle, another important factor - to what extent these acids are actually delivered to the tissues when needed - must be considered. That, in turn, raises the issues of digestion, absorption, actual bioavailability and the potential value of supplementation.

Eating quality food is the most common way to get amino acids into the diet, especially high protein foods like lean meats and nonfat dairy products. Even some vegetables and legumes can offer high levels of most amino acids. For serious athletes and those on the run, protein powders and pure free form amino acids provide a convenient and effective means to supplement dietary needs.

Why would people pay relatively large sums of money for only a few grams of pure cheaply? Because of bioavailability.

Bioavailability gauges the extent to which an administered substance reaches its site of action or utilization in the body. Bioavailability is thus a measure of the efficiency of delivery - how much of what is ingested is actually used for its intended purpose.

Conceivably, two diets could contain exactly the same amount of particular amino acids (the same amino acid profile) but have significant differences in their absorption. A number of factors affect amino acid bioavailability (see Factors Affecting Amino Acid Bioavailability.

The most reliable way to deliver specific amino acids is to administer the particular amino acids themselves. The most bioavailable source for oral use is powdered free form amino acids.

A singular (unbonded) amino acids can specifically elevate its level in the general circulation within 15 minutes, making it readily available for metabolism at the site where it's needed. Hence, for example, the recommendation to use BCAAs before, during and after training both to prevent central / mental fatigue, as well as to provide a source of energy to help prevent muscle protein catabolism and to speed recuperation.

Supplement manufacturers recognized the potential value of free-form amino use was limited by their expense and a relative lack of convincing supportive research for a number of years, their popularity has recently increased dramatically. Prepackaged workout and recovery drinks containing hydrolyzed (predigested) proteins and often some free-form amino acids now fill gym refrigerators. Capsules and powdered free-form amino acids, although still somewhat expensive, are likewise being used by increasing numbers of top amateur and professional athletes.

The value of free-form amino acids is first and foremost that they don't require digestion. The term 'free-form' means exactly that: They are free of chemical bonds to other molecules and so move quickly through the stomach and into the small intestine, where they're rapidly absorbed into the bloodstream.

Upon absorption, amino acids are processed by the liver. When you eat a steak, for example, only relatively few amino acids escape the metabolic actions of the liver. Yet the liver can process only so many at one time, and taking a dose of 3-4 grams of rapidly absorbed amino acids exceeds the liver's capacity, resulting in the aminos being directed to the tissues that require them, such as muscle in the case of bodybuilder recovering from training. Thus, the concept of 'directed amino acids'.

While sound in theory, does it work in practice? As early as 1990, the Bulgarian national weightlifting team began trials to determine if free-form amino acids were a boost to muscular growth. The work was so successful that part of the study was replicated on the Colorado Springs Olympic Training Center. Since then, top bodybuilders and powerlifters around the world today - including Mr. Olympia Dorian Yates, and 'Mr. Powerlifting' Ed Coan - have benefited from this new research.

Many misconceptions exist about the muscle contraction and the use of energy substrates during heavy during heavy, high-intensity weight training. When you're engaged in a repetitive power workout, a substantial portion of your energy comes from noncarbohydrate sources. When muscle contracts, it uses its stores of adenosine triphosphate (ATP, a substance vital to the energy processes of all living cells) for the first few seconds. The compound used to immediately replenish these stores is creatine phosphate (CP). The recent explosion of creatine supplements in the market attests to its value to hard training bodybuilders and other strength / power athletes.

CP is made from three amino acids: arginine, methionine and glycine. To keep CP and ATP levels high, these amino acids must be elevated in the bloodstream. Traditionally, these proteins have been supplied by foods in the diet. Elevating levels of these amino acids or of CP with conventional foods takes a great deal of time (for digestion) and isn't specific, typically providing levels of fats and carbohydrates that may or may not be desired. The use of free-form amino acids, alone and in combination with creatine supplements, can provide directed source of energy for power and growth.

In fat loss, two major processes must occur: 1) the mobilization and circulation of stored fats in the body must increase; and 2) fats must be transported and converted to energy at the powerhouse site of cells, the mitochondria. Several nutrients can assist in the conversion of fat to energy, including lipotropic agents such as choline, inositol and the IAA methionine which, in sufficient quantities, can help improve the transport and metabolism of fat.

Supplementation with complete IAA mixtures, BCAAs and glutamine can also help keep calorie and food volume down while providing targeted support directly to the muscles, liver and immune systems so critical to optimizing body composition.

The human body has the innate ability to break down muscle tissue for use as an energy source during heavy exercise. This muscle catabolism can cause muscle soreness, shrinkage of muscle tissue and may even lead to injury.

This enemy to bodybuilders is part of a process known as gluconeogenosis, which means producing or generating glucose from noncarbohydrate sources. The part of this reaction that of importance to bodybuilders is known as the glucose - alanine cycle, in which BCAAs are stripped from the muscle tissue and parts of them are converted to the amino acid alanine, which is transported to the liver and converted into glucose.

If you consume supplemental BCAA's. the body does not have to break down muscle tissue to derive extra energy. A study conducted recently at the School of Human Biology, University of Guelph, Onterio, Canada, confirmed that the use of BCAA's (up to 4 grams) during and after exercise can result in a significant reduction of muscle breakdown during exercise.

In addition to BCAAs, arginine is another amino acid that may benefit bodybuilders. Though it did not live up to its early hype, which touted the amino acid's ability to raise growth hormone level, new data indicate that arginine - in large but safe and affordable doses - may be able to raise GH levels by up to 1,000%.

How fat you eat a protein source and the length of time it takes for the digested amino acids to be available for use by the body are determined by a number of factors, which include:

Cooking - Amino acids are more or less sensitive to heat. For example, arginine is extremely stable and will decompose only if exposed to sustained temperatures about 470 degrees F. Carnitine decomposes at temperatures of 284 F. Cooking, in addition to killing micro-organisms, makes the long spiral polypeptide chains unwind, causing the amino acid to become more exposed when it reaches the digestive system.

Physical nature of the food, whether solid, liquid, powder or tablet; whether and to what extent chemically predigested and the type and amounts of binders, fillers and other nutritive and non-nutritive materials.

Status of the digestive system - Genetics, age, overall health and specific diseases and illnesses.

Metabolism or utilization by the intestine before absorption - such as occurs with glutamine.

Metabolism or utilization in the liver before transfer to the general circulation - For maximal directed effects, amino acids should be taken on an empty stomach and in a dosage that enables significant quantities to reach the target tissues.

Each amino acid has at least one amine and one acid functional group as the name implies. The different properties result from variations in the structures of different R groups. The R group is often referred to as the amino acid side chain. Amino acids have special common names, however, a three letter abbreviation for the name is used most of the time. A second abbreviation , single letter, is used in long protein structures.Consult the table on the left for structure, names, and abbreviations of 20 amino acids.

There are basically four different classes of amino acids determined by different side chains: (1) non-polar and neutral, (2) polar and neutral, (3) acidic and polar, (4) basic and polar.

Principles of Polarity:

The greater the electronegativity difference between atoms in a bond, the more polar the bond. Partial negative charges are found on the most electronegative atoms, the others are partially positive. Review the polarity of functional groups.

Non-Polar Side Chains:

Side chains which have pure hydrocarbon alkyl groups (alkane branches) or aromatic (benzene rings) are non-polar. Examples include valine, alanine, leucine, isoleucine, phenylalanine.

The number of alkyl groups also influences the polarity. The more alkyl groups present, the more non-polar the amino acid will be. This effect makes valine more non-polar than alanine; leucine is more non-polar than valine.

Polar Side Chains:

Side chains which have various functional groups such as acids, amides, alcohols, and amines will impart a more polar character to the amino acid. The ranking of polarity will depend on the relative ranking of polarity for various functional groups as determined in functional groups. In addition, the number of carbon-hydrogens in the alkane or aromatic portion of the side chain should be considered along with the functional group.

Example: Aspartic acid is more polar than serine because an acid functional group is more polar than an alcohol group.

Example: Serine is more polar than threonine since threonine has one more methyl group than serine. The methyl group gives a little more non-polar character to threonine.

Example: Serine is more polar than tyrosine, since tyrosine has the hydrocarbon benzene ring.

Acid - Base Properties of Amino Acids:

Acidic Side Chains:

If the side chain contains an acid functional group, the whole amino acid produces an acidic solution. Normally, an amino acid produces a nearly neutral solution since the acid group and the basic amine group on the root amino acid neutralize each other in the zwitterion. If the amino acid structure contains two acid groups and one amine group, there is a net acid producing effect. The two acidic amino acids are aspartic and glutamic.

Basic Side Chains:

If the side chain contains an amine functional group, the amino acid produces a basic solution because the extra amine group is not neutralized by the acid group. Amino acids which have basic side chains include: lysine, arginine, and histidine.

Amino acids with an amide on the side chain do not produce basic solutions i.e. asparagine and glutamine.

Neutral Side Chains:

Since an amino acid has both an amine and acid group which have been neutralized in the zwitterion, the amino acid is neutral unless there is an extra acid or base on the side chain. If neither is present then then the whole amino acid is neutral.

Amino acids with an amide on the side chain do not produce basic solutions i.e. asparagine and glutamine. You need to look at the functional groups carefully because an amide starts out looking like an amine, but has the carbon double bond oxygen which changes the property. Amides are not basic.

Capsules VS. Tablets? One of the more controversial topics regarding aminos today is capsule absorption versus the value of using tablets. In past years, capsules definitely proved to have a quicker entry time into the system. However this is no longer true. Due to advances in tabletting technology, using magnesium stearate and various brewers yeast bases, the modern tablet today can actually dissolve faster than most capsules. The true value of capsules today is the simple fact that you do not have binders, fillers or coating, some of which may contain potentially allergenic factors. Don't let yourself get caught up in the mass advertising hype pertaining to this matter. The simple truth is they are both good. It's simply your choice as to which you prefer to take. When you try to sort twenty of anything into categories there are bound to be some 'grey' cases where people disagree and the classifying of amino acids is no exception. Amino acids are generally divided into groups on the basis of their side chains (R groups). f, j, b, d, a. The most helpful start-point, in terms of the resulting properties, is to separate amino acids into those with polar side chains and those with nonpolar side chains and then to sub-divide the polar amino acids dependant upon any charge that the R group might carry. In the diagrams that follow (taken from Lehninger Principles of Biochemistry, but any standard Biochemistry textbook has similar figures), the side chains are shaded pink. This emphasises the fact that the rest of each amino acid is the same (except for Proline!) - it is only the R groups that differ. Lets start a more detailed review by considering the amino acids with nonpolar side chains. The amino acids with disputed classification will be pointed out at the appropriate times.

Even though tryptophan has an amine group as part of a five member ring, the electron withdrawing effects of the two ring systems do not allow nitrogen to act as a base by attracting hydrogen ions.

Amino acids are popularly referred to as "building blocks". Amino acids are chemical units that makeup proteins. They are composed of 16 percent nitrogen, which creates the distinguishing difference between two other basic nutrients; sugars and fatty acids. Because proteins provide the structure for all living organisms and amino acids are an essential component of protein, a person can readily understand the importance of amino acids to life in general and especially to a healthy organism. In contrast to water proteins makes up the second greatest portion of the persons body weight. This is an indicator of just how important proteins and amino acids are to the body. Proteins are substances, which makeup muscles, tendons, ligaments, organs, glands, nails, hair, vital body fluids, and bones. As you can see, proteins are really an essential component of all aspects of the body. Enzymes and hormones are actually proteins and as we know enzymes and hormones regulate all bodily processes.

Proteins form the structural basis of chromosomes, through which our genetic information is passed from parent to offspring. Embedded in the cells DNA is the actual genetic code that represents instructions on how each cell should make it's protein.

Proteins are actually a chain of amino acids linked together. Each protein is composed of specific groups of amino acids and in a specific arrangement. In this way, each protein in the body is specifically designed to fit a specific need and as a result proteins and not interchangeable. Each protein has its own unique makeup and identity.

Indeed, in-take of nutritional supplements such as vitamins and minerals must be accompanied by amino acids in order to be a simulated and absorbed by the body. Even though vitamins and minerals may be absorbed by the body they lose their effectiveness if an absence of amino acids is present.

The actual process whereby amino acids create proteins is: we take-in foods with dietary protein which is broken down into its amino acid forms which is than used by the body to build specific proteins as needed. From this vantage point one can observe the importance of amino acids as in vital nutrient.

Even in the brain, amino acids are able to pass through the blood brain barrier. In the brain, amino acids act as neurotransmitters, which facilitate the transmission of chemicals from one cell to another, enhancing communication between cells.

Approximately 28 commonly known amino acids combine to create hundreds of types of proteins found in all living things. Certain amino acids, which are not produced by organs and glands of the body, are called essential amino acids. These amino acids must be obtained through ingesting of food material into the body. The essential amino acids include histidine, isoleune, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. The remaining amino acids are referred to as nonessential. This does not mean they are not essential, it merely means, that they do not need to be obtained through diet, because the body can produce them itself.

Because the process of creating proteins is true breaking proteins into amino acids and we assembly into other proteins is ongoing, it becomes very important for the body not to run sure of material enough almost proteins to break down for assembly. From a manufacturing point of view it would be like running out of raw material use in preparation of products to be sold. A factory commits the ultimate sin if it allows itself to run out of raw material and/or inventory needed to produce its product. In the same fashion for individuals to allow the body to run out of the necessary proteins needed to be broken down in the assembled into new and diverse proteins can create severe adverse conditions. Eating a well balanced diet is essential in feeding how human machine with the necessary proteins in order for it to continue to rebuild itself daily.

Taking supplements as sources for amino acids:

Although it is not common to take supplements containing amino acids formulas, they are available. They are usually combined with other multivitamin formulas. Most amino acid supplements are derivatives of animal protein, yeast protein, or vegetable protein. When choosing amino acids supplements, it is important to find supplements of amino acids, in products containing the L.-forms of amino acids, which are considered to be more compatible with human biochemistry. Generally speaking, taking amino acids as supplements should not be taken for long periods of time. Typically, it's a good idea to alternate individual amino acids that fit your needs and back them up with amino acids complex in supplemental form, taking the supplements for two months and then skipping two months. Many researchers warn against taking large doses of amino acids over extended periods of time and stress moderation is the key. They point out, some amino acids have potential toxic effects when taken in large doses. Do not give supplemental amino acids to a child or take doses of any amino acids in excess of the recommended dosage on the label without specific directions from your physician.

Amino acids are the building blocks of protein. Twenty amino acids are needed to build the various proteins used in the growth, repair, and maintenance of body tissues. Eleven of these amino acids can be made by the body itself, while the other nine (called essential amino acids) must come from the diet. The essential amino acids are isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Another amino acid, histidine, is considered semi-essential because the body does not always require dietary sources of it. The nonessential amino acids are arginine, alanine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, proline, serine, and tyrosine. Other amino acids, such as carnitine, are used by the body in ways other than protein-building and are often used therapeutically.

Nonpolar amino acids The nonpolar amino acids are characterised by having only carbon and hydrogen in their side chains. They are generally unreactive but the fact that they are hydrophobic gives them an important role to play in determining the 3-D structure of proteins, as they tend to cluster on the inside of the molecule. The simplest amino acid is Glycine, which has a single hydrogen atom as its side chain. Alanine, Valine, Leucine and Isoleucine have saturated hydrocarbon R groups (i.e. they only have hydrogen and carbon linked by single covalent bonds). As the name implies Leucine and Isoleucine are isomers of each other. The side chain of Methionine includes a sulfur atom but remains hydrophobic in nature. The only other amino acid with a sulfur-containing side group is Cysteine. Cysteine is a 'grey' amino acid - some textbooks will classify it as nonpolar, other books as polar. Unlike Methionine, the sulfur group in Cysteine comes at the end of the hydrocarbon chain and it therefore has the potential to be more reactive (see below for more details). Three amino acids found in proteins are aromatic, that is they have a benzene-like ring structure in their side chain. They are grouped together here on the basis of this structural similarity, but as will become clear, there are significant functional differences between the three. f, f, j, l, f. The simplest case to consider is Phenylalanine. As the name should suggest to you Phenylalanine is Alanine with an extra Benzene (sometimes called a Phenyl) group on the end. Phenylalanine is highly hydrophobic and is found buried within globular proteins.

The classification of an amino acid as essential or nonessential does not reflect its importance, because all 20 amino acids are necessary for health. Instead, this classification system simply reflects whether or not the body is capable of manufacturing a particular amino acid.

Where are they found? Foods of animal origin, such as meat and poultry, fish, eggs, and dairy products, are the richest dietary sources of the essential amino acids. Plant sources of protein are often deficient in one or more essential amino acids. However, these deficiencies can be overcome by consuming a wide variety of plant foods. For example, grains are low in lysine, whereas beans provide an excess of lysine. It was previously believed that, in order for vegetarians to obtain adequate amounts of protein, all of the essential amino acids had to be “balanced” at each meal. For example, a grain and a bean had to be consumed at the same meal. However, more recent research has indicated that, while consuming a proper mix of amino acids is important, it is not necessary to consume them all at the same meal.

Who is likely to be deficient? The vast majority of Americans eat more than enough protein and also more than enough of each essential amino acid for normal purposes. Dieters, some strict vegetarian body builders, and anyone consuming an inadequate number of calories may not be consuming adequate amounts of amino acids. In these cases, the body will break down the protein in muscle tissue and use those amino acids to meet the needs of more important organs or will simply not build more muscle mass despite increasing exercise.

How much is usually taken? Nutrition experts recommend that protein, as a source of amino acids, should account for 10–12% of the calories in a balanced diet. However, requirements for protein are affected by age, weight, state of health, and other factors. On average, a normal adult requires approximately 0.36 grams of protein per pound of body weight. Using this formula, a 140-pound person would need 50 grams (or less than 2 ounces) of protein per day. An appropriate range of protein intake for healthy adults may be as low as 45–65 grams daily. Some athletes have higher amino acid requirements.2 Most American adults eat about 100 grams of protein per day, or about twice what their bodies need and at least as much as any athlete requires.

Supplements of individual amino acids are recommended by doctors for specific purposes, such as lysine for herpes or phenylalanine for pain.

Are there any side effects or interactions? Most diets provide more protein than the body needs, causing excess nitrogen to be excreted as urea in urine. The excess nitrogen has been linked in some studies with reduced kidney function in old age. Most, but not all studies have found that when people have impaired kidney function, restricting dietary intake of protein slows the rate of decline of kidney function.3

Excessive protein intake also can increase excretion of calcium, and some evidence has linked high-protein diets with osteoporosis,4 particularly regarding animal protein.5 On the other hand, some protein is needed for bone formation. A double-blind study showed that elderly people whose diets provided slightly less than the recommended amount of protein suffered less bone loss if they consumed an additional 20 grams of protein per day.6 A doctor can help people assess their protein intake.

Based on the physicochemical properties of R groups, the 20 amino acids of proteins may be classified as follows.

1. Acidic: including aspartic acid (aspartate) and glutamatic acid (glutamate). In a neutral solution, the R group of an acidic amino acid may lose a proton and become negatively charged.

2. Basic: including lysine, arginine and histidine. In a neutral solution, the R group of a basic amino acid may gain a proton and become positively charged. Interaction between positive and negative R groups may form a salt bridge, which is an important stabilizing force in proteins.

3. Aromatic: including tyrosine, tryptophan and phenylalanine. Their R groups contain an aromatic ring.

4. Sulfur: including cysteine and methionine. Their R groups contain a sulfur atom (S). The disulfide bond formed between two cysteine residues provides a strong force for stabilizing the globular structure. A unique feature about methionine is that the synthesis of all peptide chains starts from methionine (Chapter 5 Section C).

5. Uncharged hydrophilic: including serine, threonine, asparagine and glutamine. Their R groups are hydrophilic and capable of forming hydrogen bonds.

6. Inactive hydrophobic: including glycine, alanine, valine, leucine and isoleucine. These amino acids are more likely to be buried in the protein interior. Their R groups do not form hydrogen bonds and rarely participate in chemical reactions.

7. Special structure: including proline. In most amino acids, the R group and the amino group are not directly connected. Proline is the only exception among 20 amino acids found in protein. Due to this special feature, proline is often located at the turn of a peptide chain in the three-dimensional structure of a protein.

Protein Structure

The Chemical Nature of Amino Acids

The amino acids found in proteins have the following generalized structure:

where R can stand for a variety of constituents. The amino group and the carboxyl group of the amino acid have PKs of about 9.6 and 2.3 respectively. Thus, the amino acid can exist in three general forms. At low pH the amino and carboxyl groups will be protonated and the molecules will be in the acid form.

As the pH is increased towards neutrality, the amino acids become zwitterions having both negative and positive charges.

As the pH increases further, the molecules become basic.

In going from low to high pH:

When amino acids are joined together to form peptide bonds, water is removed in the following reaction:

It should be noted that the joining of amino acids to form peptide bonds eliminates the acid and basic character of the molecules. The only ionized groups in the finished protein will be the terminal amino and carboxyl groups and also any R groups that happen to contain acidic or basic groups. The Structure of Amino Acids

While there are hundreds of amino acids in nature, only 20 are commonly found in proteins. With one exception these are a amino acids that differ only in the nature of their R groups. In this section the structure of each amino acids will be given and some of the properties that are unique to that compound will be discussed. The standard three letter abbreviations for each amino acid will be given with its structure and these abbreviations will be used frequently in the remainder of the text.

Glycine

Glycine is the only amino acid that does not have optical isomers. The other amino acids do, but in proteins only the L isomer occurs. Glycine has no ionizable groups when it is located in peptide bounds. Glycine will spontaneously transfer from a non aqueous to an aqueous environment with a DF of -4.6 Kcal/mole. Because glycine contains only a hydrogen while other amino acids contain either polar or nonpolar groups, Tanford (1962) has suggested that glycine be utilized as a reference compound and that other amino acids be compared to glycine to determine the nonpolarity or hydrophobicity of their side chains. These free energy transfer values have been designated Hf. The value for glycine then is by definition zero and glycine can be expected to be found with nearly equal frequency at the interior or exterior of a protein. Due to its small size, glycine may be placed in portions of proteins where other amino acids can not occur due to steric reasons. The presence of glycine residues tends to interrupt the helical structure. Glycine is often found in portions of proteins involve in turns.

Alanine

The next largest amino acid, alanine, contains a methyl group rather than a hydrogen attached to its a carbon. Like glycine, it has no ionizable groups when it is found in proteins. Its value for Hf is 0.75 Kcal which suggests that is mildly hydrophobic. Also like glycine, alanine tends to be found with almost equal frequency on the surface and interior of protein molecules. Alanine tends to promote the formation of helical structure.

Valine

Valine has no ionizable groups when found in peptide bonds, but has considerably more bulk than either Gly or Val. Its Hf value of 1.70 Kcal suggest that it is a fairly hydrophobic residue. It is found almost exclusively in the interior of proteins. The presence of valine tends to favor the formation of helical structures.

Leucine

Leucine resembles VAL with a CH2 group before the branch. It has no ionizable groups when found in proteins and is strongly hydrophobic. It has a Hf of 2.40 Kcal and is found in the interior of protein molecules. Its presence tends to stabilize helical structures.

Isoleucine

Isoleucine is a positional isomer of LEU and thus has many of the same characteristics. The branching at the b-carbon tends to increase its bulk and thus its hydrophobicity. Isoleucine has the second highest Hf of 2.95 Kcal, has no ionizable groups when found in proteins and tends to stabilize helical structures.

Serine

Serine resembles ALA with a hydroxyl group. It is a neutral polar molecule that tends to remain on the surface of proteins (Hf < O). The presence of serine tends to interrupt helical structures. While generally present on the surface, serine can be found on the interior of protein when its -OH group is involved in hydrogen bond formation. Serine can also form noncovalant cross links between protein links between protein chains due to hydrogen bonding.

Threonine

Threonine is closely related to SER in that only a methyl group has been added to the molecule. The hydroxyl group tends to make the molecule polar while the ethyl group tends to be non-polar. Threonine has an Hf of 0.45 Kcal but tend to be found on the surface of proteins unless its hydroxyl group is hydrogen bounded. The presence of threonine neither favors nor inhibits the formation of helical structure and threonine has no ionizable groups when found in protein molecules. Like SER, threonine can be used to form hydrogen bond cross-links between protein chains.

Phenylalanine

Phenylalanine is a bulky amino acid with a strong hydrophobic character. Its Hf is 2.65 Kcal and this residue is found almost exclusively in the interior of protein molecules. It has no ionizable groups but does contain the conjugated ring system with its p electrons are also able to interact with other molecules containing p electrons. Phenylalanine neither favors nor inhibits the formation of helical structure. This residue can be found both at the surface and interior of protein molecules.

Tyrosine

Tyrosine strongly resembles PHE but contains a hydroxyl group on the ring. The bulky ring gives the molecule a hydrophobic nature with Hf of 2.85 Kcal. The hydroxyl group is polar and will readily interact with water. The conjugated ring's p electrons are also able to interact with other molecules containing p electrons. Tyrosine neither favors nor inhibits the formation of helical structure. This residue can be found both at the surface and interior of protein molecules. When found in the interior, its hydroxyl group is always involved in hydrogen bonding. At very high pH values the hydroxyl of PHE can be ionized and thus the molecule can be considered as weakly acidic. The pk of this group is around 9.6 when tyrosine is located in a protein and thus at neutral pH values, the molecule is essentially unionized. Tyrosine absorbs strongly in the ultraviolet region and thus contributes to the UV absorbance of proteins.

Tryptophan

The tryptophan is the bulkiest amino avid and has a Hf of 3.0 Kcal. In spite of its very hydrophobic nature, it is found both on the surface and interior of protein molecules. Its extensive array of p electrons allows it to interact strongly with other molecules containing p electrons. Tryptophan has no ionizable groups and tends to favor the formation of helical structures. Tryptophan absorbs strongly in the region between 275 and 280 nM and makes a large contribution to the ultraviolet absorption of protein molecules.

Cysteine

Cysteine is a slightly acidic amino acid that is slightly hydrophobic with an Hf of 1.0 Kcal. The presence of cysteine neither favors nor inhibits the formation of helical structures. Probably the most important characteristic of cysteine is its ability to stabilize protein structure by forming disulfide linkages with other cysteine molecules. These covalent cross links add stability to the three dimensional structures of protein and their formation and importance will be discussed in some detail in the next chapter. The sulfhydryl group of cysteine is a very weak acid with a pK of about 8.4. At a pH near neutrality, a few percent of the sulfhydryl groups of a protein will be ionized.

Methionine

Methionine is a neutral amino acid with a Hf of 1.3 Kcal. It is related to cysteine but can not form disulfide linkages. Methionine tends to favor the formation of helical structures. While not able to cross link proteins through disulfide linkages, the molecule can form important interactions with other constituents that may bind to proteins. The sulfur atoms of methionine contains a pair of nonbonded electrons that are capable of binding to metals to make methionine a metal ligand.

Proline

Proline is not a primary amine, but rather a secondary amine or an imine. Peptide bonds formed with proline lack a free amino group to form hydrogen bonds and thus proline tends to strongly inhibit a helical structure. These peptide bonds tend to fold back upon themselves and proline is found quite often in regions or protein that form turns. Proline has not ionizable groups and has Hf of 2.6 Kcal.

Aspartic Acid

Aspartic acid is one of the two dicarboxylic amino acids. The second carboxly group makes the molecule very hydrophillic. It has a Hf < 0. The pK of the second group is about 3.85 and thus aspartic acid contains a negative charge at neutral pH. Removal of this charged group from the aqueous phase requires a large expenditure of energy and thus charged amino acids are found almost exclusively at the surface of proteins. This group is able to form ionic bonds with positively charged amino acids or metals and it can also form ion dipole interactions with water. These interactions are very important to the solubility properties of proteins. The pressures of aspartic acid neither favors nor inhibits the formation of helical structures.

Glutamic Acid

Glutamic acid is very similar to aspartic acid in its structure and its properties. It contains one more CH2 group, but still has a Hf < 0. The carboxyl group is less acidic than is that of ASP with a pK of 4.25. The differences are not great, however, and at neutral pH dissociation is virtually complete. The presence of glutamic acid tends to favor the formations of helical structures and like ASP, it is involved in many interactions.

Asparagine

Asparagine resembles ASP but the carboxyl group has been neutralized by formation of an amide bond., Some amino acids are modified after the protein is assembled, eg. hydroxylation of some proline residues, methylation of some histidines, etc. These changes are not determined by the genetic code but rather are performed by specific enzymes that recognize certain amino acid sequences. This is not the case for asparagine and this amino acid is inserted as such during protein synthesis. Even without the free carboxyl group asparagine is a polar molecule that is almost always found at the protein surface. It can function as a chain crosslinker via hydrogen bond formation or it can hydrogen bond to water at the protein surface. Asparagine tends to inhibit the formation of helical structure and quite often is found in protein bends.

Glutamine Much as asparagine resembles ASP , Glutamine resembles GLU. Again the carboxyl group has been neutralized by formation of an amide bond. Like asparagine, glutamine is almost always found at the protein surface. It can function as a chain crosslinker via hydrogen bond formation or it can hydrogen bond to water at the protein surface. Glutamine tends to favor the formation of helical structures in proteins.

Histidine

Histidine can bind a proton to the nonbonded electron pair of its ring nitrogen to become a weak acid at low pH. The pK of the acid is 6.0 so that at neutral pH, histidine is about 90% in the basic form with about 10% still in the acid form. Histidine is the only amino acid that has a functional group that titrates in the physiological pH range. It is a polar molecule, Hf < O that tends to favor the formation of helical structure. Depending upon its form, which depends on the localized pH of its environment, histidine can serve as both a proton donor and accepter. The nonbonded electron pair of the basic form are always available for metal chelation. This versatility has been utilized and histidine is quite often found at the active site of enzymes and as a point of attachment for metal containing group.

Arginine

Arginine is a large polar molecule with a positive charge at neutral pH. The pK of the guanidanyl group is about 12.5. Even though the molecule has a positive charge at almost all pH values, arginine is a very large molecule and has an Hf of 0.75 Kcal. Arginine tends to interact with negatively charged groups, negative ions and with water.

Lysine

Lysine is a charged polar amino acid having an extra amino group. The pK of this group is about 10.5 and thus lysine will have a positive charge at the pH values that most proteins are likely to encounter. Lysine is a bulky molecule with a Hf of 1.5 Kcal. Lysine neither favors nor inhibits the formation of helical structure and is capable of interacting with groups that have negative charges and with water.

Tyrosine is Phenylalanine with an extra hydroxyl (-OH) group attached and in consequence has significantly different properties. It is polar and very weakly acidic. Tyrosine can play an important catalytic role in the active site of some enzymes (e.g. the bacterial enzyme DNA gyrase) and in keeping with Serine and Threonine, two other amino acids that have hydroxyl groups on their side chain, Tyrosine can be chemically modified after it has been incorporated into a peptide chain. A kinase enzyme (e.g. Wee1 involved in control of the cell cycle in yeast) can chemically link a phosphate group via the hydroxyl oxygen in a process called phosphorylation. The process can be reversed by a phosphatase enzyme (e.g. Cdc25 which reverses the effect of Wee1). This type of modification of tyrosine and even more so modification of threonine and serine residues has proven to be extraordinarily important in the regulation of the activity of different proteins. Tryptophan is far more like Phenylalanine than Tyrosine. It is hydrophobic and tends to be found buried inside globular proteins. Tryptophan is also structurally related to Alanine, but with a two ring (bicyclic) indole group added in place of the single aromatic ring found in Phenylalanine. The presence of the nitrogen group makes Tryptophan a little less hydrophobic than Phenylalanine. Polar uncharged amino acids These are amino acids that possess oxygen, sulfur and/or nitrogen in the side chain and are therefore polar, but cannot have their R group ionised (see below) and thus do not carry an overall charge. The polar nature of the side chain means that these amino acids readily interact with water, i.e. they are hydrophilic. Serine and Threonine were mentioned above in the context of proteins regulated by phosphorylation. They are also very important in the active sites of many enzymes (e.g. chymotrypsin). Cysteine is not very polar, and is often classified as nonpolar. d, i, b, i, j. It is most important for its ability to link to another cysteine via the sulfur atoms to form a covalent disulfide bridge, important in the formation and maintenance of the tertiary (folded) structure in many proteins. Proline is also classified as nonpolar in many textbooks. It is unique amongst the amino acids found in proteins because its side chain is bonded to the backbone nitrogen as well as to the a-carbon. Because of this proline is technically an imino rather than an amino acid. The ring is not reactive, but it does restrict the geometry of the backbone chain in any protein where it is present.

In 1929 British biochemist John Haldane (1892-1964) put forth the theory that the early atmosphere of Earth contained no free oxygen. Haldane and Soviet biochemist Aleksander Oparin (1894-1980) had both suggested that all the ingredients for life existed on Earth from the beginning and that energy from the sun and some unknown process had gotten life started.

In 1952 American chemist Harold C. Urey (1893-1981) published an elaboration of Haldane's theory, suggesting that Earth had formed from a cold stellar dust cloud. Its early atmosphere was then roughly similar to that of the rest of the universe -- that is, mostly hydrogen with traces of other elements. Urey figured that the trace oxygen, nitrogen, and carbon would be bound with hydrogen and exist as water, ammonia, and methane. With so much hydrogen around, free oxygen could not exist (it would always get bound up with hydrogen and form water). But as time went by (lots of time), many of the extremely light hydrogen atoms escaped into outer space until the balance changed. Without an excess of hydrogen, free oxygen could exist and gradually accumulate in Earth's atmosphere.

Stanley Miller (b. 1930) was a doctoral student working with Urey at the University of Chicago, researching possible environments of early Earth. In 1953 he combined the ideas of Urey and Oparin in a short, simple experiment.

He reproduced the early atmosphere of Earth that Urey proposed by creating a chamber with only hydrogen, water, methane, and ammonia. To speed up "geologic time" in his experiment, he boiled the water and instead of exposing the mix to ultraviolet light he used an electric discharge something like lightning. After just a week, Miller had a residue of compounds settled in his system. He analyzed them and the results were electrifying: Organic compounds had been formed, most notably some of the "building blocks of life," amino acids. Amino acids are necessary to form proteins which themselves form the structure of cells and play important roles in the biochemical reactions life requires. Miller found the amino acids glycine, alanine, aspartic and glutamic acid, and others. Fifteen percent of the carbon from the methane had been combined into organic compounds. As amazing as discovering amino acids at all was how easily they had formed.

That same year, the structure of DNA was elucidated, revealing even more strikingly the crucial role of very basic organic compounds. It also revealed a way in which some compounds -- nucleic acids -- could replicate and keep life going. The base pairs within DNA, which actually transfer the genetic code, are made of simple nitrogen-based compounds. Later researchers using techniques like Miller's were able to synthesize many of the components of DNA from gases thought to be present in the early atmosphere. In 1960 Juan Oró synthesized adenine, one of DNA's four bases and also a key component of ATP (adenosine triphosphate), an energy-carrier in cell respiration.

Miller's work showed that compounds necessary for life could have been formed in an environment without free oxygen, confirming Haldane's theory. The creation of amino acids from Earth's raw materials may well have been the first step of evolution. It also opens the possibility (since the proposed atmosphere was based on proportions of elements in the universe) that similar atoms and amino acids could have formed elsewhere, on planets formed in the same manner as Earth.

Asparagine and Glutamine are the amide derivatives of Aspartate (Aspartic acid) and Glutamate (Glutamic acid) - see below. Unlike the parent acids, Asparagine and Glutamine cannot be ionised and are therefore uncharged. Amino acids are known as the building blocks of protein, and are defined as the group of nitrogen-containing organic compounds composing the structure of proteins. They are essential to human metabolism, and to making the human body function properly for good health. Of the 28 amino acids known to exist, eight of them are considered "essential," defined as those that can be obtained only through food. These essential amino acids are tryptophan, lysine, methionine, phenylalaine, threonine, valine, leucine, and isoleucine. The "non-essential" amino acids include arginine, tyrosine, glycine, serine, glutmamic acid, aspartic acid, taurine, cycstine, histidine, proline, alanine, and creatine, which is a combination of arginine, glycine, and methionine. The human body, minus water, is 75% amino acids. All of the neurotransmitters (proteins) but one are composed of amino acids; and 95% of hormones are amino acids. Amino acids are key to every human bodily function with every chemical reaction that occurs. Amino acids occur naturally in certain foods, such as dairy products, meats, fish, poultry, nuts, legumes, and eggs. Those sources are considered more complete than vegetable protein, such as beans, peas, and grains, also considered a good--even if not complete--source of amino acids. k, c, e, l, e. Amino acids became popular as dietary supplements by the end of the twentieth century for various uses, including fitness training, weight loss, and certain chronic diseases. Claims exist in holistic medicine that indicate amino acid supplements taken in the proper dosage can aid also in fighting depression, allergies, heart disease , gastrointestinal problems, high cholesterol, muscle weakness, blood sugar problems, arthritis, insomnia, bipolar illness, epilepsy, chronic fatigue syndrome, autism, attention deficit hyperactivity disorder (ADHD), and mental exhaustion.

Amino acids definition: Organic compounds that combine to form proteins.

Acetyl L-carnitine Acetyl L-carnitine is a molecule composed of acetic acid and L-carnitine bound together. This amino acid, which is structurally similar to acetylcholine (a neurotransmitter in the brain responsible for memory and normal brain function), plays an important role in treating diseases like Alzheimer's disease, senile depression, and age-related memory defects. Many studies have shown that Acetyl L-carnitine can have the same benefits and effects of acetylcholine in stimulating brain cell production, in stabilizing cell membranes, and in acting as a powerful antioxidant to the brain.

One study of Alzheimer's sufferers showed that patients who took two grams of Acetyl L-carnitine daily for one year scored better on fourteen different tests than those who took the placebo. In another study of elderly patients with mild memory deterioration, the patients demonstrated significant improvement in mental function after taking 1,500 mg of Acetyl L-carnitine on a daily basis. Another group of elderly patients suffering from depression also saw significant improvement when they took 500 mg of Acetyl L-carnitine three times daily.

Alanine An important source of energy for muscle tissue, the brain and central nervous system; strengthens the immune system by producing antibodies; helps in the metabolism of sugars and organic acids.

Arginine Arginine significantly contributes to insulin production, muscle metabolism, liver lipid metabolism, and is a component of collagen. It enhances the immune system, specifically by stimulating the thymus gland and the manufacture of T cells. This increase in T cell activity can be effective in fighting bacteria, viruses, cancer tumor cells, AIDS, chronic fatigue, and other immune system related health challenges.

Arginine is a factor for maintaining the nitrogen balance in muscles; and can enhance the lean tissue to fat tissue body fat ratio; a great factor for weight management.

Arginine also neutralizes ammonia, which helps in liver detoxification and regeneration. As a component of collagen, it can assist with wound healing, skin problems, arthritis, and connective tissue problems.

Asparagine This amino acid is found mostly in meat sources, so vegetarians might need to consider supplementation. Asparagine balances the central nervous system and prevents excess nervousness/anxiety or excessive calmness/depression.

Aspartic Acid Aids in the expulsion of harmful ammonia from the circulatory system. When ammonia enters the circulatory system it acts as a highly toxic substance which can be harmful to the central nervous system and cause neural and brain disorders. Aspartic acid deficiency decreases cellular energy and may likely be a factor in chronic fatigue.

Plants, especially sprouting seeds, are abundant in aspartic acid.

Carnitine Anyone concerned with decreasing body fat will want to assure their daily level of carnitine, because carnitine helps TRANSPORT FAT from fat cells to the mitochondria of muscle cells so it can be BURNED UP FOR ENERGY. It is hard to imagine how a weight loss program could ever be effective with a deficiency of carnitine.

Current levels of excessive body fat in the general population indicate a high level of carnitine deficiency. Interestingly, carnitine is not part of the "essential" nutrient group because the body manufactures it. But the manufacturing process requires adequate iron, Vitamin B1, B6, and C, and the amino acids lysine and methionine (neither of these amino acids are obtainable in sufficient amounts from vegetable sources). Carnitine deficiency will result if any of those nutrients are at inadequate levels, so supplementation is absolutely essential, especially for vegetarians.

Carnitine is great nutrient for diabetes prevention since poor fat metabolism is a causative factor for the development of diabetes. It is also great for heart disease prevention because it lowers triglycerides, improves organ muscle strength and enhances the antioxidant effectiveness of Vitamins C and E. Also, studies indicate that cardiac surgery damages to the heart can be reduced with carnitine treatments.

Recent research has shown that at high doses (1,000- 3,000 mg. daily), carnitine acts as an agent to reduce blood triglycerides. ELevated triglycerides can lead to an increased risk of small vessel diseases, including poor circulation in the hands and feet as well as kidney problems.

Citrulline Functions primarily in the liver. Like other amino acids, citrulline detoxifies ammonia is involved in the energy cycle, and enhances the immune system.

Cysteine and Cystine These amino acids are structured very closely and convert into each other as needed. They are involved in collagen production for skin elasticity and texture, and for alpha-keratin for fingernails, toenails, and hair. In fact, hair and skin are made up of 10-14% Cystine. This makes supplemental cysteine great for burn and surgery recovery, it is also recommended in treating rheumatoid arthritis.

Cysteine is a powerful free radical destroyer by itself, but works best when vitamin E and selenium are present. It helps detoxify and protect the body from radiation damage, so it is often used in conjunction with chemotherapy and radiation cancer treatments.

Cysteine is a precursor to the liver detoxifying and antioxidant amino acid glutathione. This functionality provides an anti-aging effect on the body—even reducing the accumulation of age spots. Another impressive function is the break down of mucus in the respiratory tract which can help in bronchitis, emphysema, and tuberculosis.

N-acetylcysteine is the best form of cysteine supplementation and has been proven more effective at increasing glutathione levels than supplements of glutathione itself, or supplements of just L-cysteine.

Caution: Cystinuria is a genetic disease where cystine kidney stones are formed. People with this disease should not take supplemental cysteine.

Dimethylglycine (DMG) Participates in formation of methionine, choline, DNA, and several neurotransmitters. DMG is good for the heart. It has been found to lower blood cholesterol and triglycerides, and help normalize blood pressure and blood glucose.

Gamma-Aminobutyric Acid (GABA) GABA functions in the central nervous system as a neurotransmitter; it occupies the nerve receptor sites for anxiety or stress related messages so that they are restrained from reaching the brain.

GABA can be taken as a tranquilizer to calm the body, but without the addiction that can come with usage of Valium™ or Librium™. GABA is also used for epilepsy, hypertension, and ADD-ADHD.

Balanced supplementation is important because too much GABA can increase anxiety, and cause numbness in the face and tingling in the fingers and toes.

Amino acid therapy as a supplemental aid to a healthy diet joined the fitness craze in the United States by the end of the 1990s. According to author Brenda Adderly in Better Nutrition, in September of 1999, "The creation of new protein from amino acids and the breaking down of existing protein into amino acids are ongoing processes in our bodies. If, for example, you are working out and developing certain muscles, amino acids come to the rescue with new protein to build muscle cells," Adderly noted. "Similarly, when you eat a complete protein, such as meat or beans and rice, the body breaks down the amino acids in that food for later use." Understanding the balance of amino acids in the body can be often the first clue to understanding why a person suffers many ailments, ranging from depression to upset stomach to obesity. Deficiencies in the proper balance of amino acids is likely to occur in those with poor diets. Because stress, age, infection, and various other factors including the amount of exercise a person does, can also affect the levels of amino acids, people with healthy, nutritious diets could also find that they also suffer deficiencies. Adderly adds that, "Not only are the symptoms of amino acid deficiencies wide ranging, but there are no RDAs (recommended daily allowances) or other guidelines, to help us tell if we are least covering all the bases. Add to that the complicated matter of keeping track of all 28 some with names most of us have never even heard and the situation begins to seem overwhelming." One of the most discussed amino acid supplements available on the market is creatine monohydrate. The body produces small amounts of creatine in the kidneys, liver, and pancreas, making it a non-essential acid. With most diets that include red meat or fish, they also include a few grams of creatine. l, c, g, h, i. It is stored in muscle cells and is used in activities, such as weight lifting and sprinting, providing the necessary thrust of energy for such activities. But the natural supply of creatine produced by the body is quickly depleted. After approximately 10 seconds, when muscle fatigue becomes apparent, the daily production is used.

Glutamic Acid Glutamic Acid is the precursor of GABA but has somewhat the opposite function; it is an excitatory neurotransmitter. It is one of the few nutrients that crosses the blood-brain barrier and is the only means by which ammonia in the brain can be detoxified.

It is considered to be nature's "Brain food" by improving mental capacities; and is used in the treatment of depression, ADD and ADHD, fatigue and chronic fatigue, alcoholism, epilepsy, muscular dystrophy, mental retardation, and schizophrenia.

Glutamine Glutamine readily passes the blood-brain barrier and increases the amount of glutamic acid and GABA; thereby enhancing normal nervous system function. As amino acids chemically change, ammonia is released. Glutamine plays a role in the removal of this toxic ammonia from the brain.

Because glutamine's role in the nervous system is so important, during times of stress, illness, or surgery up to one third of the muscle stores of glutamine are released for nervous system usage; causing extensive muscle deterioration and loss. The muscle glutamine release is much lower if glutamine levels are increased through supplemental L-glutamine.

Supplemental L-glutamine is also used therapeutically for arthritis, autoimmune diseases, developmental disabilities, impotence, schizophrenia, and for tissue damage from cancer radiation treatments.

Caution: Supplemental glutamine should not be taken by anyone with a disproducts/productsindex that causes an accumulation of ammonia in the blood (kidney or liver problems, Reye's syndrome, etc.)

Glutathione The liver produces glutathione from the amino acids cysteine, glutamic acid and glycine. Glutathione deficiency results in early aging and in the loss of coordination, balance, tremors, and mental disorders.

Glutathione levels decline with age and if not corrected will accelerate the aging process; so supplementation is important. But the assimilation of supplemental oral glutathione is questionable. Instead it is best to supplement with cysteine, glutamic acid and glycine and have the body use those raw materials to manufacture needed glutathione.

Glycine Glycine supplies additional creatine to muscles and is used to construct DNA and RNA. It functions in skin, connective tissues, the central nervous system and prostate.

A proper level of cellular glycine produces more energy, but too much glycine can cause fatigue.

Histidine Is found abundantly in red and white blood cells and is a component of the myelin sheaths that protect nerve cells. It is used in the treatment of arthritis, allergies, and ulcers.

Histamine, a chemical that functions in the immune system, is derived from histidine. Besides functioning in the immune system, histamine aids in sexual arousal, functioning and pleasure. To form histimine, histidine requires vitamins B3 and B6.

Caution: Histidine levels that are too high may lead to stress and psychological disorders like anxiety and schizophrenia. Individuals with manic (bipolar) depression should not take supplemental histidine unless prescribed by their health care provider.

Isoleucine One of three branched-chain amino acids (the others are leucine and valine) that enhance energy, increase endurance, and aid in muscle tissue recovery and repair. This group also lowers elevated blood sugar levels and increases growth hormone production. Supplemental isoleucine should always be combined with leucine and valine at a respective milligram ratio of 1:2:2.

Caution: Megadosing causes symptoms of hypoglycemia, pellagra, and may result in excessive levels of ammonia in the body.

Leucine One of three branched-chain amino acids (the others are isoleucine and valine) that enhance energy, increase endurance, and aid in muscle tissue recovery and repair. This group also lowers elevated blood sugar levels and increases growth hormone production. Supplemental leucine should always be combined with isoleucine and valine at a respective milligram ratio of 2:1:2.

Caution: Megadosing causes symptoms of hypoglycemia, pellagra, and may result in excessive levels of ammonia in the body.

Lysine Lysine is especially needed for adequate absorption of calcium and bone development in children. It aids in the production of antibodies, hormones & enzymes. Recent studies have shown that Lysine may be effective against herpes by improving the balance of nutrients that reduce viral growth.

A deficiency may result in tiredness, inability to concentrate, irritability, bloodshot eyes, retarded growth, hair loss, anemia & reproductive problems.

Methionine This amino acid is a principle supplier of sulfur, which inactivates free radicals. Adequate methionine prevents disorders of the hair, skin and nails; helps lower cholesterol levels by increasing the liver's production of lecithin; reduces liver fat and protects the kidneys.

Methionine is a natural chelating agent for heavy metals and helps detoxify the body of these metals. It regulates the formation of ammonia and creates ammonia-free urine which reduces bladder irritation. It also influences hair follicles and prevents brittle hair.

Ornithine Ornithine participates in the release of growth hormone, which then prompts the metabolism of excess body fat. This process is enhanced by the presence of arginine and carnitine. Caution: Children, pregnant or nursing women, or anyone with a history of schizophrenia should only use supplemental L-ornithine under the direction of a physician.

Phenylalanine Used by the brain to produce dopamine and norepinephrine, chemicals that promote alertness, elevate mood, decrease pain, aid in memory and learning, and reduce hunger and appetite.

Caution: Phenylalanine should not be supplemented by individuals with anxiety attacks, diabetes, pigmented melanoma (skin cancer), high blood pressure, or if pregnant.

Proline Is obtained primarily from meat and aids in maintaining collagen (skin protein). Proline deficiency will cause an uncareful vegetarian to have early signs of skin aging. Proline also strengthens joints, tendons, connective tissue, and cartilage.

Serine A storage source of glucose by the liver and muscles; helps strengthen the immune system by providing antibodies; synthesizes fatty acid sheath around nerve fibers.

Taurine Helps stabilize the excitability of membranes which is very important in the control of epileptic seizures. Taurine and sulfur are considered to be factors necessary for the control of many biochemical changes that take place in the aging process; aids in the clearing of free radical wastes. A deficiency of zinc and taurine may impair vision.

It is used theraputically for people with hypertension, aterosclerosis, edema, cardiac arrhythmias, anxiety, epilepsy, hyperactivity, seizures, breast cancer, Down syndrome, muscular dystrophy.

Taurine is in eggs, fish, meat, and milk, but not in vegetable proteins. It can be synthesized from cysteine and methionine as long as sufficient quantities of vitamin B6 are present.

Threonine Is an important constituent of collagen, elastin, and enamel protein; helps prevent fat build-up in the liver; helps the digestive and intestinal tracts function more smoothly; assists metabolism and assimilation.

Tryptophan A natural relaxant, helps alleviate insomnia by inducing normal sleep; reduces anxiety and depression; helps in the treatment of migraine headaches; helps the immune system; helps reduce the risk of artery and heart spasms; works with lysine in reducing cholesterol levels.

Tyrosine Promotes the healthy functioning of the thyroid, adrenal and pituitary glands. Supresses the appetite and helps to reduce body fat. Research indicates tyrosine may help chronic fatigue, narcolepsy, anxiety, depression, allergies, headaches, and Parkinson's disease.

Amino Acids are the building blocks for all proteins. Amino acids contain a nitrogen group, which is unique to each different amino acid, and an acid group. The nitrogen and acid groups can be linked in any number of ways to form thousands of specific proteins. Amino acids help build cells, repair tissue, form anitbodies, build RNA and DNA, carry oxygen throughout the body and aid muscle activity. There are 9 amino acids that are essential, meaning your body cannot manufacture them. They must come from the foods you eat. The 9 essentials are: Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan and Valine.

There are 11 non-essential amino acids, which means your body can manufacture them on its own. The 11 non-essentials are: Alanine, Arginine, Asparagine, Aspartic Acid, Glutamine, Glycine, Proline, Serine, Tyrosine, Cysteine and Glutamic Acid. The last two can become essential during stressful times, such as severe illness. ** There are other amino acids, but unlike the 20 listed above, they do not built protein.

Federal Trade Commission lawyer Michell Rusk said there is a big problem with misleading information about dietary supplements, including vitamins, minerals and amino acids. "Too many advertisements go beyond the actual scientific evidence and misrepresent the facts," Rusk said. For example, in 1995, Nature's Bounty Inc. settled FTC charges of 26 exaggerated health claims for dietary supplements. Among the claims were statements that advertised benefits of certain amino acids. The products, called L-Arginine and L-Ornithine, were advertised to increase muscle mass while decreasing body fat.

Everybody has heard the term "amino acid" a million times, but really is an amino acid? Amino acids are the building blocks of proteins, which carry out many functions in organismic life. Some proteins act as catalysts, others serve for storage and transport, while still others are antibodies for our immune system. There are also numerous other functions that different proteins execute. The point is, amino acids are absolutely essential to cellular life. Chemically speaking, amino acids are carboxylic acids which have an amine group attached to it.

Amino acids are a biochemical building block. They form long chemical chains called proteins, and shorter chains called peptides. In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups. In biochemistry, this shorter and more general term is frequently used to refer to alpha amino acids: those amino acids in which the amino and carboxylate functionalities are attached to the same carbon.

Twenty amino acids are encoded by the standard genetic code and are called proteinogenic. Proline is the only cyclic proteinogenic amino acid. Other amino acids contained in proteins are usually formed by modification after translation (protein synthesis). These modifications are often essential for the function of the protein. At least two amino acids other than the standard 20 are sometimes incorporated into proteins during translation:

Selenocysteine is incorporated into some proteins at a UGA codon, which is normally a stop codon. Pyrrolysine is used by some methanogens in enzymes that they use to produce methane. It is coded for similarly to selenocysteine but with the codon UAG instead.

Over 500 amino acids have been found in nature. Some of them have also been found in meteoritic material. Microorganisms and plants often produce very uncommon amino acids, which can be found in peptidic antibiotics (for example nisin or alamethicin). Lanthionine is a sulfide bridged alanine dimer which is found together with unsaturated amino acids in lantibiotics (antibiotic peptides from microbial origin). 1-Aminocycloproane-1-carboxylic acid ACC is a small disubstituted cyclic amino acid and a key intermediate in the production of the herbal hormone ethylene.

In addition to amino acids for protein synthesis, there are other biologically important amino acids, such as the neurotransmitter GABA, carnitine (used in lipid transport within a cell), ornithine, citrulline, homocysteine, hydroxyproline, hydroxylysine, and sarcosine.

All peptides and polypeptides are polymers of alpha-amino acids. There are 20 a-amino acids that are relevant to the make-up of mammalian proteins. Several other amino acids are found in the body free or in combined states (i.e. not associated with peptides or proteins). These non-protein associated amino acids perform specialized functions. Several of the amino acids found in proteins also serve functions distinct from the formation of peptides and proteins, e.g., tyrosine in the formation of thyroid hormones or glutamate acting as a neurotransmitter.

The a-amino acids in peptides and proteins (excluding proline) consist of a carboxylic acid (-COOH) and an amino (-NH2) functional group attached to the same tetrahedral carbon atom. This carbon is the a-carbon. Distinct R-groups, that distinguish one amino acid from another, also are attached to the alpha-carbon (except in the case of glycine where the R-group is hydrogen). The fourth substitution on the tetrahedral a-carbon of amino acids is hydrogen.

Each of the 20 a-amino acids found in proteins can be distinguished by the R-group substitution on the a-carbon atom. There are two broad classes of amino acids based upon whether the R-group is hydrophobic or hydrophilic. The hydrophobic amino acids tend to repel the aqueous environment and, therefore, reside predominantly in the interior of