What Is Prokaryote?

Prokaryotes are mostly unicellular organisms without a nucleus, in contrast to eukaryotes, organisms that have cell nuclei and may be variously unicellular or multicellular. The difference between prokaryote and eukaryote cell structure is the most important in the living world. Most prokaryotes are bacteria, and the two terms are often treated as synonyms. However, Woese has proposed dividing them into the Bacteria and Archaea (originally Eubacteria and Archaebacteria) on the supposition that these have separate origins. This controversial arrangement is called the three-domain system.

Prokaryotes do not develop or differentiate into multicellular forms. Some bacteria grow in filaments, or masses of cells, but each cell in the colony is identical and capable of independent existence. The cells may be adjacent to one another because they did not separate after cell division or because they remained enclosed in a common sheath or slime layer secreted by the cells. Typically though, there is no continuity or communication between the cells. Prokaryotes are capable of inhabiting almost every place on the earth, from the deep ocean, to the edges of hot springs, to just about every surface of the human body.

The name prokaryote comes from the Greek pros meaning before and karyon meaning nut, referring to the nucleus. Prokaryotes also lack cytoskeletons and membrane-bound cell compartments such as vacuoles, endoplasmic reticulum, mitochondria and chloroplasts. In eukaryotes, the latter perform various metabolic processes and are believed to have been derived from endosymbiotic bacteria. In prokaryotes similar processes occur within the cell membrane, and endosymbionts are extremely rare. They are usually much smaller than eukaryotic cells.

Prokaryotes have a single chromosome, contained within a nucleoid region rather than a membrane-bound nucleus, but may also have various small circular pieces of DNA called plasmids spread throughout the cell. Reproduction is exclusively asexual, through binary fission, where the chromosome is duplicated and attaches to the cell membrane, and then the cell divides in two. However, they show a variety of parasexual processes where DNA is transferred between cells, such as transformation and transduction.

Eukaryotes are organisms with complex cells, in which the genetic material is organized into membrane-bound nuclei. They include the animals, plants, and fungi, which are mostly multicellular, as well as various other groups called protists, many of which are unicellular. In contrast, other organisms such as bacteria lack nuclei and other complex cell structures, and are called prokaryotes. The eukaryotes share a common origin, and are often treated formally as a superkingdom, empire, or domain. The name comes from the Greek eus or true and karyon or nut, referring to the nucleus.

It is generally accepted that the first living cells were some form of prokaryote, and they are known as fossils from over 3.5 billion years ago. Some have suggested structures within a Martian meteorite should be interpreted as fossil prokaryotes, but this is extremely doubtful.

After the first prokaryotes evolved, they subsequently have had an explosion of diversification during the ages. The metabolism of prokaryotes is the most diverged and cause some prokaryotes to be very different from each other.

The prokaryotes consist of millions of genetically-distinct unicellular organisms. What they lack in structural diversity, so well-known among eukaryotes (including the protista), they make up for in their physiological diversity. It is often a particular physiological trait that unifies and distinguishes a particular group of prokaryotes to microbiologists. In Bergey's Manual of Determinative Bacteriology (1994), the identifiable groups of prokaryotes are assembled based on easily-observed phenotypic characteristics such as Gram stain, morphology (rods, cocci, etc), motility, structural features (e.g. spores, filaments, sheaths, appendages, etc.), and on distinguishing physiological features (e.g. anoxygenic photosynthesis, anaerobiasis, methanogenesis, lithotrophy, etc.).

The Archaea are not eukaryotes, which makes them prokaryotes. However, the fact that they are related to Eucarya, not to the other prokaryotic organisms (the Bacteria), means that prokaryotes are not a natural group. This is difficult to fully appreciate, since we tend to accord a special status to eukaryotic cells. It is perhaps most easily understood by considering the ability to learn about one group from another:

If we wonder about a biosynthetic reaction in a eukaryote, it makes more sense to use a member of the Archaea as a model than to use a member of the Bacteria. Even though much more money is being spent on analysis of eukaryotic genomes than prokaryotic genomes, due to their smaller size, some prokaryotic genomes will be completed first. Of these, it appears that we will learn more about human genes from the archaeal genomes than from the bacterial genomes.

If we wonder about transcription initiation in Thermococcus celer (an archaeon), should we look at what is known about transcription in E. coli (another prokaryote) or in yeast (a eukaryote)? It is now known that the transcription apparatus of T. celer seems to be much more similar to that of yeast than to that of E. coli.

Prokaryotic cells may have photosynthetic pigments, such as is found in cyanobacteria ("blue bacteria"). Some prokaryotic cells have external whip-like flagella for locomotion or hair like pili for adhesion. Prokaryotic cells come in multiple shapes: cocci (round), baccilli (rods), and spirilla or spirochetes (helical cells).

There are three domains of life that have or had a prokaryotic grade of organisation:

Archaea (Archaeobacteria, which have an anaerobic metabolism), Eubacteria ("true" bacterial and blue-green algae), and the hypothetical Urkaryote organism (which, it is believed, enetered into a symbiotic relationship with several different prokaryote species to form the first eukaryote cell

Prokaryotes are unicellular organisms, found in all environments. Prokaryotes are the largest group of organisms, mostly due to the vast array of bacteria which comprise the bulk of the prokaryote classification. Characteristics:

No nuclear membrane (genetic material dispersed throughout cytoplasm) No membrane-bound organelles Simple internal structure Most primitive type of cell (appeared about four billion years ago) Examples:

Staphylococcus Escherichia coli (E. coli) Streptococcus

In the world of cells, there are two major groups: the prokaryotes and the eukaryotes. They are very similar in that they contain many of the same parts. However, there are a few major differences between them.

Eukaryotes contain membrane-bound nuclei and other organelles, while prokaryotes lack this membrane-bound nucleus. Prokaryotes are classified in two kingdoms separate from the eukaryotes. Eukaryotes are the type of cells that make up plants and one celled organisms, but not animals.

The reason that they have a membrane-bound nucleus is because they have to carry out all the processes of life, which is untrue in prokaryotes. Prokaryotes rely on many cells working together to function. While eukaryotes are radically different from one another, they do have three general parts that allow them to carry out these processes of life. These are the cell membrane, the nucleus, and other organelles. The organelles are very important to the cell’s functioning.

Some of these organelles include mitochondria, which transfer energy from organic compounds to ATP. The ribosomes organize the synthesis of proteins (which is used to get energy). The rough endoplasmic reticulum prepares proteins for export. The smooth endoplasmic reticulum regulates calcium levels, breaks down toxic substances, and synthesizes steroids. The golgi body processes and packages substances produced by the cell. The lysosomes digest molecules.

There are other little parts to the cells which aid in all of this. These include microfilaments, cilia, flagella (those two assist in transportation), and of course the nucleus. In a plant, there are also the cell wall, the vacuole, and the plastid. All of these organelles are used to carry out the life processes.

Prokaryotes and Eucaryotes:

The Cell Membrane encloses the cell. Water and nutrients are admitted through the cell wall, and wastes are expelled. Bacteria and plant cells also have a protective cell wall, but animals have a membrane without a wall.

Cytoplasm is the watery stuff that fills the cell, provides a medium in which to move the molecules around. The cytoplasm is full of chemicals: dissolved oxygen and / or carbon dioxide, amino acids, simple sugars, molecules of carbohydrates, proteins, or lipids (fats). More than half of the cell contents is water.

In eukaryotes the inside of the cell is full of membranes that guide and contain and compartmentalize the cell contents.

Ribosomes do protein synthesis. I think of them as being like workers in a fast food place. When the cell needs proteins, the ribosomes get information about how to make the proteins by copying a piece of the DNA. That is like taking the order.

The proteins are made of amino acids, which are floating in the cytoplasm. The ribosome collects the amino acids which fill the order. It puts the amino acids together correctly. That is like assembling and packing up the items on the order.

When the order is complete, the protein folds up and is ready to use. The folding up is the customer's smile!

Prokaryota means "before a nucleus".

Prokaryotes are single-celled organisms. They are the smallest, simplest organisms.

The group includes bacteria (or eubacteria) and archaea.

They are abundant in the air, water, soil, and on most objects.

Prokaryotes are small (0.5 - 1.5 microns).

A plasma membrane surrounds the cell.

Prokaryotes have no membrane-bound organelles such as a nucleus, mitochondria, chloroplasts, golgi apparatus, or endoplasmic reticulum.

Many enzymes such as those needed in cellular respiration are attached to the plasma membrane. In eukaryotes, the enzymes needed for cellular respiration are located within the mitochondrion.

Photosynthetic forms do have membraneous vesicles where photosynthetic pigments (chlorophyll) are located. These structures are called thylakoids.

Ribosomes are the only cytoplasmic organelles. They are smaller than eukaryote ribosomes.

The nucleoid is a region where the circular chromosome (DNA) is located.

Plasmids are accessory rings of DNA. Some biotechnology techniques involve the use of plasmids as vectors to insert foreign DNA into the bacteria. For example, human genes are inserted into bacteria by first splicing them into a plasmid. The plasmid is then taken up by a bacterium.

They usually have a cell wall. It prevents bursting or shrinking when the osmotic concentration changes.

The cell is surrounded by a capsule (attached) and/or by a loose gelatinous sheath (slime layer).

Some move by means of flagella. The flagellum contains a hook and a basal body. It rotates 360° to propel the cell.

Many adhere to surfaces by short hair-like structures called fimbriae.

Prokaryotes are very small cells that have no membrane around their nucleus nor any organelles. Prokaryotes include bacteria. They are the simplest organisms on Earth, and also the commonest. Every part of your skin is smothered in them. Their spores fill the air we breathe. Every glass of water we drink, even good clean drinking water, contains millions of them. On the outside they have a strong cell wall. Beneath this is a membrane which will allow oily molecules to pass but prevents electrically charged molecules, and free protons and electrons, from passing through. Beneath this is a watery space full of molecules and ribosomes, messenger nucleic acids and all the other things needed to keep life going, all mixed up in a mostly chaotic way. There are some organelles within the cell, which function as storage compartments, but these do not have a membrane surrounding them as they do in eukaryotes. Instead they are surrounded by a protein coat.

At the center of the prokaryote is the nuclear region, but not separated from the rest of the cell by a membrane. This contains the DNA of the prokaryote, which is a long strand with its ends fixed together. The prokaryote may also contain shorter sequences of DNA called plasmids. These can move from one cell to another and carry information how to make proteins which inactivate antibiotics, for example.

At one end of the prokaryote there may be a wonderful little motor with a long stiff strand attached to it on the outside of the cell. As the motor rotates this strand is twirled around and pushes the cell along. So some prokaryotes can swim! The rod is called a flagellum or 'whip'.

In times of hardship, prokaryotes can shut down most of their life processes and wrap themselves up in a very hard outer coating.

Procaryotes are unicellular organisms of relatively simple construction, especially if compared to eukaryotes. Whereas eukaryotic cells have a preponderance of organelles with separate cellular functions, procaryotes carry out all cellular functions as individual units. A procaryotic cell has five essential structural components: a genome (DNA), ribosomes, cell membrane, cell wall, and some sort of surface layer which may or may not be an inherent part of the wall. Other than enzymatic reactions, all the cellular reactions incidental to life can be traced back to the activities of these macromolecular structural components. Thus, functional aspects of procaryotic cells are related directly to the structure and organization of the macromolecules in their cell make-up, i.e., DNA, RNA, phospholipds, proteins and polysaccharides. Diversity within the primary structure of these molecules accounts for the diversity that exists among procaryotes.

At one time it was thought that bacteria were essentially "bags of enzymes" with no inherent cellular architecture. The development of the electron microscope, in the 1950s, revealed the distinct anatomical features of bacteria and confirmed the suspicion that they lacked a nuclear membrane. Structurally, a procaryotic cell (Figure 1 below) has three architectural regions: appendages (attachments to the cell surface) in the form of flagella and pili (or fimbriae); a cell envelope consisting of a capsule, cell wall and plasma membrane; and a cytoplasmic region that contains the cell genome (DNA) and ribosomes and various sorts of inclusions. In this chapter, we will discuss the anatomical structures of procaryotic cells in relation to their adaptation, function and behavior in natural environments.

Most procaryotes have a rigid cell wall. The cell wall is an essential structure that protects the cell protoplast from mechanical damage and from osmotic rupture or lysis. Procaryotes usually live in relatively dilute environments such that the accumulation of solutes inside the procaryotic cell cytoplasm greatly exceeds the total solute concentration in the outside environment. Thus, the osmotic pressure against the inside of the plasma membrane may be the equivalent of 10-25 atm. Since the membrane is a delicate, plastic structure, it must be restrained by an outside wall made of porous, rigid material that has high tensile strength. Such a material is murein, the ubiquitous component of bacterial cell walls.

The cell walls of bacteria deserve special attention for several reasons: 1. They are an essential structure for viability, as described above. 2. They are composed of unique components found nowhere else in nature. 3. They are one of the most important sites for attack by antibiotics. 4. They provide ligands for adherence and receptor sites for drugs or viruses. 5. They cause symptoms of disease in animals. 6. They provide for immunological distinction and immunological variation among strains of bacteria.

The cell walls of all Bacteria contain a unique type of peptidoglycan called murein. Peptidoglycan is a polymer of disaccharides (a glycan) cross-linked by short chains of amino acids (peptides), and many types of peptidoglycan exist. All Bacterial peptidoglycans contain N-acetylmuramic acid, which is the definitive component of murein. The cell walls of Archaea may be composed of protein, polysaccharides, or peptidoglycan-like molecules, but never do they contain murein. This feature distinguishes the Bacteria from the Archaea.

The cytoplasmic constituents of procaryotic cells invariably include the procaryotic chromosome and ribosomes. The chromosome is typically one large circular molecule of DNA, more or less free in the cytoplasm. Procaryotes sometimes possess smaller extrachromosomal pieces of DNA called plasmids. The total DNA content of a procaryote is referred to as the cell genome. During cell growth and division, the procaryotic chromosome is replicated in the usual semi-conservative fashion before for distribution to progeny cells. However, the eukaryotic processes of meiosis and mitosis are absent in procaryotes. Replication and segregation of procaryotic DNA is coordinated by the membrane, possibly by mesosomes.

The distinct granular appearance of procaryotic cytoplasm is due to the presence and distribution of ribosomes The ribosomes of procaryotes are smaller than cytoplasmic ribosomes of eukaryotes. procaryotic ribosomes are 70S in size, being composed of 30S and 50S subunits. The 80S ribosomes of eukaryotes are made up of 40S and 60S subunits. Ribosomes are involved in the process of translation (protein synthesis), but some details of their activities differ in eukaryotes, Bacteria and Archaea. Protein synthesis using 70S ribosomes occurs in eukaryotic mitochondria and chloroplasts, and this is taken as a major line of evidence that these organelles are descended from procaryotes.

The two major kinds of cells are prokaryotic cells and eukaryotic cells. The prokaryotic cell is the simplest of the two cell types. Prokaryotes have no true nucleus (Greek pro = before, karyon = kernel (nucleus)). Instead, their genetic material is found as circular DNA in the nucleoid region with no nuclear membrane to isolate it from the rest of the cell. Prokaryotes also do not have membrane-bound organelles as do eukaryotes. They use free ribosomes to synthesize proteins. Prokaryotes also have a plasma membrane surrounding the entire cell, and most prokaryotes have a cell wall. The Kingdom Monera is the only place where prokaryotes are found. This means that all archaebacteria and eubacteria are prokaryotes. A handful of dirt has more prokaryotes in it than the amount of people who have ever walked the earth.

Prokaryotes are the single-celled organisms, such as bacteria, and are roughly one micrometer in diameter. Unlike Eukoryotes, prokaryotes do not have a nucleus that houses its genetic material. Rather, the genetic material of a prokaryote cell consists of a large DNA molecule compacted in an area of cytoplasm called the nucleiod region. The nucleoid region is protected and encased by the cell wall, or cell membrane, the outer layering of the cell (similar to human's skin). Finally, a flagellum (flagetta - plural), a rudder-like device, affords the prokaryote the luxury of mobility.

One differentiating characteristic is that prokaryotes are asexual, meaning their offspring nearly always bear the exact characterisitcs of the parent cell. (In fact, the cell essentially replicates itself according to its own DNA and then divides itself from the newly created cell.) Since the Prokaryotes exhibit this asexual behavior as opposed to sexual behavior, where a recombination of chromosones occur to form unique entities (as with humans), evolution of the prokaryotic cell has been fairly stagnant over its two billion year lifespan. Additionally, at the time of Symbiosis, prokaryotes were anaerobic, that is, they did not respirate oxygen as a fundamental necessity to live. As far as nutrition distribution, the small size of prokaryotes provides a high ratio of surface area to volume, making diffusion an adequate means for distributing nutrients throughout the cell.

Abundance. Prokaryotic cells and fossils have have been found in almost every conceivable environment on the earth, from hot sulfur springs to beneath the ocean floor and within larger cells. Overall, Prokaryotes account for a significant portion of the past and present biomass on earth.

Prokaryotes are single-celled organisms distinguished from single- and multi-celled eukaryotes by a number of features. The name refers to the absence of a membrane bound structure (nucleus) enclosing the genetic material. The name is derived from the Greek words pro, meaning before (in time or position), and karuon, meaning nut or kernal (referring to the nucleus). Prokaryotes have a single circular chromosome, sometimes called a genophore to distinguish it from structurally dissimilar eukaryotic chromosomes. In most the genophore is located in a nucleoid region, distinguished in electron micrographs by less intense staining than the surrounding cytoplasm. Prokaryotes also lack endoplasmic reticulum and organelles characteristic of most eukaryotes. Most prokaryote cells are smaller than eukaryotes, on the order of 1 - 5 micrometers, compared to 10 - 100 micrometers. As always in the realm of life however, there are exceptions. One type of rod-shaped prokaryote found in marine environments is about half of millimeter (500 micrometers) in length! Although prokaeryotes are thought of as single-celled organisms, some live in transient aggregations, and some form true colonies. In some of the colonial forms there is even functional specialization among two or more different cells, a kind of simple multicellular organization.

In the three domain system the term prokaryote is used to describe the chief morphological characteristic of organisms in the domains Archaea and Bacteria, and is not applied to any taxonomic category. In the system of Margulis and Schwartz Archaea and Bacteria are subkingdoms in the superkingdom Prokarya.

Many people are only familiar with prokaryotes, bacteria, as disease causing organisms. Many kinds of bacteria are pathogens of humans and other eukaryotes, but the vast majority are not. Prokaryotes are also ecologically important as photosynthetic or chemosynthetic producers, as decomposers, and as participants in the global cycling of nutrients such as carbon, nitrogen, and sulfur. Indeed, without decomposition by prokaryotes, releasing nutrients for uptake by other organisms, or without the chemical conversions of carbon and nitrogen compounds, other organisms could not exist.

The names of the two major classes of cells—eukaryotes and prokaryotes—betray certain scientific assumptions about how the two are organized. Eukaryotes include all of the cells of plants and animals and are distinguished from the prokaryotic cells of bacteria by their structural complexity. Specifically, eukaryotic cells contain membrane-bounded compartments in which specific metabolic activities take place. Most important among these is the presence of a nucleus, the membrane-delimited compartment that houses the eukaryotic cell's DNA. It is this nucleus that gives the eukaryote—literally, true nucleus—its name. In contrast the prokaryote cell contains no membrane-delimited compartments and thus its name reflects its status as the proto-eukaryote. Most dangerous about these names is that they allow scientists to make assumptions about the way metabolism is carried out inside each cell type. In stark contrast to the eukaryote, the prokaryote has long been thought of as just a bag of enzymes in which reactions take place almost by random encounters.

Prokaryote: A unicellular organism lacking a nuclear membrane, a discrete nucleus, and other specialized compartments within the cell. Bacteria and viruses are prokaryotes.

It appears that life arose on earth about 4 billion years ago. The simplest of cells, and the first types of cells to evolve, were prokaryotic cells. Bacteria are the best known and most studied form of prokaryotic organisms, although the recent discovery of a second group of prokaryotes, called archaea, has provided evidence of a third cellular domain of life and new insights into the origin of life itself.

Prokaryotes are unicellular organisms that do not develop or differentiate into multicellular forms. Some bacteria grow in filaments, or masses of cells, but each cell in the colony is identical and capable of independent existence. The cells may be adjacent to one another because they did not separate after cell division or because they remained enclosed in a common sheath or slime secreted by the cells. k, j. Typically though, there is no continuity or communication between the cells. Prokaryotes are capable of inhabiting almost every place on the earth, from the deep ocean, to the edges of hot springs, to just about every surface of our bodies.

Prokaryotes are distinguished from eukaryote on the basis of nuclear organization, specifically their lack of a nuclear membrane. Prokaryotes also lack any of the intracellular organelles and structures that are characteristic of eukaryotic cells. Most of the functions of organelles, such as mitochondria, chloroplasts, and the Golgi apparatus, are taken over by the prokaryotic plasma membrane. Prokaryotic cells have three architectural regions: appendages called flagella and pili--proteins attached to the cell surface; a cell envelope consisting of a capsule, a cell wall, and a plasma membrane; and a cytoplasmic region that contains the cell genome (DNA) and ribosome and various sorts of inclusions.

Prokaryotes are mostly unicellular organisms without a nucleus, in contrast to eukaryotes, organisms that have cell nuclei and may be variously unicellular or multicellular. The difference between prokaryote and eukaryote cell structure is the most important in the living world. Most prokaryotes are bacteria, and the two terms are often treated as synonyms. However, Woese has proposed dividing them into the Bacteria and Archaea (originally Eubacteria and Archaebacteria) on the supposition that these have separate origins. This controversial arrangement is called the three-domain system. The name prokaryote comes from the Greek pros meaning before and karyon meaning nut, referring to the nucleus. Prokaryotes also lack cytoskeletons and membrane-bound cell compartments such as vacuoles, endoplasmic reticulum, mitochondria and chloroplasts. In eukaryotes, the latter perform various metabolic processes and are believed to have been derived from endosymbiotic bacteria. In prokaryotes similar processes occur within the cell membrane, and endosymbionts are extremely rare. They are usually much smaller than eukaryotic cells.

Prokaryotes have a single chromosome, contained within a nucleoid region rather than a membrane-bound nucleus, but may also have various small circular pieces of DNA called plasmids spread throughout the cell. Reproduction is exclusively asexual, through binary fission, where the chromosome is duplicated and attaches to the cell membrane, and then the cell divides in two. However, they show a variety of parasexual processes where DNA is transferred between cells, such as transformation and transduction.

It is generally accepted that the first living cells were some form of prokaryote, and they are known as fossils from over 3.5 billion years ago. Some have suggested structures within a Martian meteorite should be interpreted as fossil prokaryotes, but this is extremely doubtful.

Archaebacteria and Eubacteria also known as the "prokaryotes" and are usually referred to as bacteria are structurally the simplest kinds of organism. They resemble the earliest forms of life. Most are unicellular with cell membrane and a rigid cell wall. There are no mitochondria, chloroplasts, nuclei, or other membrane bound organelles within the cell. The DNA exists as one large, circular molecule suspended in the cytoplasm. The DNA is not associated with histone proteins and does not form into chromosomes. Reproduction in bacteria is by fission (cell division). Most bacteria are heterotrophic so they need to gain nutrients from the environment. Many are saprophytic, meaning they send out digestive enzymes into the environment and thereafter take up the digested nutrient molecules. Some bacteria are parasitic and can only survive on other living organisms. Some are pathogens that cause diseases such as strep throat or gangrene. Other bacteria are autotrophic, meaning they can produce their own food. Autotrophic bacteria can be either photosynthetic utilizing energy from the sun or chemosynthetic utilizing energy from non-organic chemical reactions. Eubacteria are the most numerous organisms on earth and they flourish in almost every environment. Billions of them can be found in a handful of soil. d, d, k. They are also found in your digestive tract, on your skin, and between your teeth. Archaebacteria are found in extreme environments such as hydrothermal vents on the ocean floor which reach temperatures well in excess of 100°C, and within cracks of rocks in the Antarctic desert - the driest and coldest place on earth. Archaebacteria are also fount in such extremes as salty water, anaerobic water, or water rich in sulfur.

The timescale of prokaryote evolution has been difficult to reconstruct because of a limited fossil record and complexities associated with molecular clocks and deep divergences. However, the relatively large number of genome sequences currently available has provided a better opportunity to control for potential biases such as horizontal gene transfer and rate differences among lineages. We assembled a data set of sequences from 32 proteins (~7600 amino acids) common to 72 species and estimated phylogenetic relationships and divergence times with a local clock method.

Kingdom Monera: The Prokaryotes.

The Monerans are the most numerous and widespread organisms on earth. They comprise the only kingdom of prokaryotic organisms, those which lack a nucleus or other membrane-bounded organelles. External to the plasma membrane, most bacteria have a cell wall partially composed of peptidoglycan, a complex structural molecule not found in eukaryotic cells. Let's have a look at the basic flavors of bacteria.

ARCHAEBACTERIA There are three types of archaebacteria, the most ancient of all living things. The thermoacidophiles live in the extremely hot, acidic water and moist areas within and surrounding sulfur hot springs. So closely adapted are they to their bubbly environment that they die of cold at temperatures of 55oC (131oF)! Methanogens are obligate anaerobes (free oxygen kills them) which oxidize CO2 during cellular respiration to produce methane (CH4) as a waste product. l, b, h, k, a. Although RNA sequencing suggests that all ten known species are evolutionarily related, they exist in environments as diverse as scalding volcanic deep-sea vents and the intestines of mammals. The reason you can light a puff of flatulence (should you choose to go into show business) is because of the symbiotic methanogens inside your guts.

Strict halophiles live in extremely salty solutions such as the Dead Sea, the Great Salt Lake and that can of pickled herring you left open in the cupboard. Their pink carotenoid pigments make them conspicuous when the bacteria are present in large concentrations, as they are on the shores of some salty, land-locked lakes.

EUBACTERIA The "true bacteria" are classified on the basis of several characteristics, of which perhaps the most familiar is the Gram Stain method.

Gram negative Eubacteria About 75% of known eubacteria are gram negative. They include the gliding bacteria, the spirochetes, the curved (vibrios) and spiral (spirillae) bacteria, gram-negative rods, gram-negative cocci, rickettsias, chlamydias and the photosynthetic cyanobacteria. Gram negative bacteria form an extremely diverse group. The fact that they are all gram-negative does not necessarily imply that they comprise a monophyletic taxon.

Gram positive Eubacteria Not as diverse as the gram-negative bacteria, the gram-positives still make up an impressively varied group. This division includes the gram-positive rods, gram-positive cocci, and the actinomycetes, which exhibit superficial similarity and function (but no evolutionary relationship) to the (eukaryotic) fungi. 

MYCOPLASMAS These are the smallest living cells ever discovered, and are believed to have the minimum amount of DNA needed to code for a functioning cell. They lack the cell wall characteristic of the other three types of bacteria. Most mycoplasmas exist as intracellular plant or animal parasites, a life history which protects them from environmental osmotic stresses as long as the host cell is functioning properly. Penicillin, an antibiotic lethal to most other bacteria because it interferes will cell wall formation, is not effective against the naked little mycoplasmas.

Archaea - these organisms are microscopic prokaryotes. When the first ones were discovered (in 1977), they were considered bacteria. However, when their ribosomal RNA was sequenced, it became obvious that they bore no close relationship to the bacteria and were, in fact, more closely related to the eukaryotes (including ourselves!) For a time they were referred to as archaebacteria, but now to emphasize their distinctness, we call them Archaea

Bacteria and archaea belonging to deep-branching lineages in rDNA-based phylogenies frequently share common phenotypic and metabolic properties. These in turn suggest inferences about their ancestral geochemical environments. Although there is considerable metabolic diversity among the energy metabolisms of early diverging bacteria and archaea (sulfur reduction, methanogenesis, fermentation of organic carbon compounds, hydrogen oxidation), anaerobiosis and thermophily emerge as common themes, possibly connected to complex CO2/H2 autotrophy. A systematic molecular survey of prokaryotic biodiversity within anaerobic and/or hot marine environments, such as gradient habitats of hydrothermal vent sites, stratified marine water columns and anaerobic sediments, will show in greater detail the connection between microbial metabolisms and habitats, and the limits of prokaryotic tolerance towards extreme environments.

By examining the evolution of microorganisms in these habitats, we will also gain a better understanding of how their evolution was connected to the evolution of an oxygen-rich atmosphere.

The combined results of these biodiversity surveys with molecular and cultivation approaches will delineate habitat range and environmental tolerance limits of prokaryotic and eukaryotic populations in situ.

Cyanobacteria are Prokaryotes, which are known to be the earliest forms of life, throughout time they have adapted to the changing earth, and in turn help it evolve. Prokaryotes belong to the kingdom Monera (Greek for single) and are small celled organisms that lack membrane-enclosed organelles. They have cell walls, but their composition differs from those of plants, protisits and fungi. They are similar to Eukaryotes, but they have smaller and simpler genomes, and differ in genetic replication, protein synthesis, and recombination. Prokaryotes are photosynthetic and aquatic and can exist in almost any environment, and individually their impact may be microscopic, but collectively their impact on the earth is immense. Prokaryotes are divided based on the differences on how they receive their nutrition (how they obtain energy and carbon). Cyanobacteria belong to the category termed photoautorophs, which use light to drive the synthesis of organic compounds from carbon dioxide.

The prokaryotes include the bacteria and the bluegreen bacteria (or "algae") and the prochlorons. There are several different groups of bacteria and they are probably no closer related to each other than they are to the Cyanobacteria but we will consider them together for convenience.

PROKARYOTE CHARACTERISTICS

Prokaryotic cells differ from Eukaryotic cells in several important respects, many of which have already been considered.

1. Size. They are usually much smaller then eukaryotes. 1-5m m rather than 10-100 of eukaryotes. Most are about 1m m.

2. They have no envelope-surrounded nucleus.

3. Their DNA has much less protein associated with it and what is present is easily dislocated. Consequently prokaryotes were long thought to have no protein associated with the DNA.

4. The DNA is a continuous loop, or circle. Smaller circles, or plasmids, may be present.

5. There is no mitosis or meiosis but there is, of course, chromosome replication. Division is by binary fission.

6. There are no independent internal membranes and consequently no membrane surrounded organelles. Thus there are no chloroplasts, mitochondria, lysosomes, endoplasmic reticulum, Golgi.

7. The enzymes, pigments, and electron carriers usually associated with membranes are located on invaginations of the plasma membrane known as mesosomes.

8. The cell wall is unique. It is not cellulose rather another polymer of glucose-like monomers. The polymer is known as a peptidoglycan. These are polymers of substituted glucose crosslinked by short polypeptides. They are known as N-acetylglucosamine and N-acetylmuramic acid. In gram negative bacteria there is also an outer layer of polysaccharide. Protects from lysis in hypoosmotic environment.

9. The cell membrane and cytoplasm are similar to those of eukaryotes except that there is no cytoskeleton in the cytoplasm and no steroids in the membrane.

10. The ribosomes are smaller.

11. There is much less DNA. There is about 1mm of DNA in an E. coli cell whereas one of your cells has about 2m.

12. The flagellum, if present, is radically different from that of eukaryotes. There is no tubulin/dynein system. The flagellum is made of flagellin, and is naked protein outside the membrane.

There are more then 10,000 species of bacteria and their classification is based largely on clinical and laboratory convenience rather than phylogeny. Recent molecular systematic studies have shed some light on the relationships within the Monera.

There apparently was a very early split of the monerans into the Archaebacteria and the Eubacteria. Most modern bacteria are Eubacteria and the Archaebacteria persist as a small number of species largely restricted to extreme environments such as hot springs, high salinities, high acidities, anaerobic environments, etc. e, g, a, d, f. Archaebacteria have no peptidoglycan in the cell wall and have unique phospholipids in the membrane. Ribosomal proteins resemble those of eukaryotes and the archaebacteria may be more closely related to Eukaryotes than are the eubacteria.

The Eubacteria include the gram positive bacteria as well as many groups of gram negative bacteria, the photosynthetic bacteria as well as the Cyanobacteria and spirochaetes.

Any of a group of relatively simple one-celled living things lacking a nucleus and other features found in the more complex cells of all other living things, called eukaryotes. The two major types of prokaryotes are bacteria and cyanobacteria.

The prokaryotes known as archaebacteria are primitive anaerobes (living things that do not require oxygen ) inhabiting extreme environments of high temperature, high salt, or high acidity. All other bacteria are called eubacteria and are classified according to their shape: for example, bacilli are rod-shaped. Eubacteria live in both aerobic (with oxygen) and anaerobic (without oxygen) environments.

Some prokaryotes move by rotating long whip-like structures called flagella. Some species also have slender hair-like extensions called pili, used for attachment. The cell membrane of prokaryotes, similar in structure to that of eukaryotes, is different in composition. Eukaryotes contain organelles, including chloroplasts and mitochondria, that are absent in prokaryotes. Prokaryotes have a single molecule of deoxyribonucleic acid (DNA). This DNA molecule is not enclosed in a nucleus, is not associated with protein, and is not double-stranded, as it is in eukaryotes.

Prokaryotes are cellular organisms lacking a true nucleus and nuclear membrane. Their nuclear material consists of a single double-stranded DNA molecule, not associated with basic proteins. The microorganisms, comprising the bacteria and blue-green bacteria (formerly blue-green algae), are predominantly unicellular but may have filamentous, mycelial, or colonial forms. All (except the Mollicutes and Archaeobacteria) have a true cell wall containing peptidoglycan, and all reproduce by cell fission.

Prokaryotes are the original inhabitants of this planet, the first successful today's would have looked very like some of today's Archaea. Both Archaea and Bacteria evolved somewhere between 3 or 4 billion years ago as far as we are able to tell from the fossil record. This means they have been around twice as long as the Protozoans and more than 3 times as long as animals.

Prokaryotes are the toughest of the tough when it come to living things. They hold all the records for living in the coldest, hottest, most acidic and most highly pressurized environments. They live in incredible places such as miles beneath the earth in bare rock, under glaciers, floating around in clouds and miles down on the sea floor at temperatures greater than 100 C. They are also the worlds experts at surviving bad times. In 2000AD scientists at W