Cell structure of a bacterium, one of the two groups of prokaryotic life. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have

The prokaryotes (pronounced /proʊˈkærioʊtiːz/; singular prokaryote /proʊˈkæriət/) are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles. In Cell biology, the nucleus (pl nuclei; from Latin la ''nucleus'' or la ''nuculeus'' "little nut" or kernel is a membrane-enclosed The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer In Cell biology, an organelle (pronunciation /ɔː(rgəˡnɛl/ is a specialized subunit within a cell that has a specific function and is usually separately enclosed They differ from the eukaryotes, which have a cell nucleus. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Most are unicellular, but some prokaryotes are multicellular organisms. A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually The word prokaryotes comes from the Old Greek pro- before + karyon nut or kernel, referring to the cell nucleus, + suffix -otos, pl. -otes; it is also spelled "procaryotes". Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly Nut is a general term for the large dry oily Seeds or Fruit of some Plants. A seed (in some plants referred to as a kernel) is a small embryonic Plant enclosed in a covering called the seed coat usually with some stored In Grammar, a suffix (also postfix, ending) is an Affix which is placed at the end of a word Plural is a Grammatical number, typically referring to more than one of the Referent in the real world ^[1]

The prokaryotes are divided into two domains: the bacteria and the archaea. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Archaea are a newly appointed domain of life. In biological Taxonomy, a domain (also superregnum, superkingdom, or empire) is the highest Taxonomic rank of Organisms These organisms were originally thought to live only in inhospitable conditions such as extremes of temperature, pH, and radiation but have since been found in all types of habitats. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature pH is the measure of the acidity or alkalinity of a Solution. Radiation, as in Physics, is Energy in the form of waves or moving Subatomic particles emitted by an atom or other body as it changes from a higher energy A habitat (which is Latin for "it inhabits" is an Ecological or environmental area that is inhabited by a particular Species.

Relationship to eukaryotes

A distinction between prokaryotes and eukaryotes (meaning true kernel, also spelled "eucaryotes") is that eukaryotes do have "true" nuclei containing their DNA, whereas the genetic material in prokaryotes is not membrane-bound. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Eukaryotic organisms may, as in the case of amoebae, be unicellular or, as in the case of humans, be multicellular. Amoeba (sometimes amœba or ameba, plural amoebae) is a Genus of Protozoa that moves The difference between the structure of prokaryotes and eukaryotes is so great that it is considered to be the most important distinction among groups of organisms. In 1977, Carl Woese proposed dividing prokaryotes into the Bacteria and Archaea (originally Eubacteria and Archaebacteria) because of the major differences in the structure and genetics between the two groups of organisms. Carl Richard Woese (born July 15 1928, Syracuse New York) is an American Microbiologist who attended Deerfield Academy The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have This arrangement of Eukaryota (also called "Eukarya"), Bacteria, and Archaea is called the three-domain system replacing the traditional two-empire system. The three-domain system is a Biological classification introduced by Carl Woese in 1990 that divides cellular life forms into Archaea, The two-superkingdom system (or two-empire system was the top-level biological classification system in general use before the establishment of the Three-domain system. A criticism of this classification is that the word "prokaryote" itself is based on what these organisms are not (they are not eukaryotic), rather than what they are (either archaea or bacteria).

The cell structure of prokaryotes differs greatly from that of eukaryotes. The defining characteristic is the absence of a nucleus. In Cell biology, the nucleus (pl nuclei; from Latin la ''nucleus'' or la ''nuculeus'' "little nut" or kernel is a membrane-enclosed Instead, the genomes of prokaryotes are held within an irregular DNA/protein complex in the cytosol called the nucleoid, which lacks a nuclear envelope. In classical genetics the genome of a Diploid Organism including Eukarya refers to a full set of chromosomes or genes in a Gamete, thereby Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl The cytosol or intracellular fluid (or cytoplasmic matrix) is the liquid found inside cells. In Prokaryotes, the nucleoid (meaning nucleus-like) is an irregularly-shaped region within the cell of Prokaryotes where the Genetic material The nuclear envelope (NE(also known as the perinuclear envelope, nuclear membrane, nucleolemma or karyotheca) is a double lipid bilayer that ^[2] Prokaryotes generally lack membrane-bound cell compartments: such as mitochondria and chloroplasts. In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. Chloroplasts are Organelles found in Plant cells and eukaryotic Algae that conduct Photosynthesis. Instead processes such as oxidative phosphorylation and photosynthesis take place across the prokaryotic plasma membrane. Oxidative phosphorylation is a Metabolic pathway that uses energy released by the oxidation of Nutrients to produce Adenosine triphosphate (ATP Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer ^[3] However, prokaryotes do possess some internal structures, such as vacuole and cytoskeletons,^[4][5] and the bacterial order Planctomycetes have a membrane around their nucleoid and contain other membrane-bound cellular structures. In general vacuole functions include Removing unwanted structural debris Isolating materials that might be harmful or a threat to the cell Containing cytoskeleton (also CSK is a cellular " Scaffolding " or " Skeleton " contained within the Cytoplasm. Planctomycetes are a Phylum of aquatic Bacteria and are found in field samples of brackish, and marine and fresh Water ^[6] Both eukaryotes and prokaryotes contain large RNA/protein structures called ribosomes, which produce protein. Ribonucleic acid ( RNA) is a Nucleic acid that consists of a long chain of Nucleotide units Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Ribosomes ( from ribo nucleic acid and "Greek soma ( meaning body") are complexes of RNA and Protein that Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Prokaryotes are usually much smaller than eukaryotic cells. ^[1]

Prokaryotes also differ from eukaryotes in that they contain only a single loop of stable chromosomal DNA stored in an area named the nucleoid, while eukaryote DNA is found on tightly bound and organized chromosomes. In Prokaryotes, the nucleoid (meaning nucleus-like) is an irregularly-shaped region within the cell of Prokaryotes where the Genetic material A chromosome is an organized structure of DNA and Protein that is found in cells. Although some eukaryotes have satellite DNA structures called plasmids, these are generally regarded as a prokaryote feature, and many important genes in prokaryotes are stored on plasmids. A plasmid is an extra-chromosomal DNA molecule separate from the chromosomal DNA which is capable of replicating independently of the chromosomal DNA ^[1]

Prokaryotes have a larger surface area to volume ratio giving them a higher metabolic rate, a higher growth rate and consequently a shorter generation time compared to Eukaryotes. Basal metabolic rate ( BMR) is the amount of energy expended while at rest in a neutrally temperate environment in the post-absorptive state (meaning that the digestive system ^[1]

Sociality

While prokaryotes are still commonly imagined to be strictly unicellular, most are capable of forming stable aggregate communities. When such communities are encased in a stabilizing polymer matrix (“slime”), they may be called “biofilms”. A biofilm is a structured community of Microorganisms encapsulated within a self-developed polymeric matrix and adherent to a living or inert surface Cutting edge research shows that, like those in multicellular organisms, cells in biofilms often show distinct patterns of gene expression (phenotypic differentiation) in time and space. Multicellular organisms are Organisms consisting of more than one cell, and having Differentiated cells that perform specialized functions Gene expression is the process by which inheritable information from a Gene, such as the DNA sequence, is made into a functional Gene product, such Also, like multicellular eukaryotes, these changes in expression appear to often result from cell-to-cell signaling, a phenomenon known as quorum sensing. Cell signaling is part of a Complex system of Communication that governs basic cellular activities and coordinates cell actions Quorum sensing is a type of decision-making process used by decentralized groups to coordinate behavior

Biofilms may be highly heterogeneous and structurally complex and may attach to solid surfaces, or exist at liquid-air interfaces, or potentially even liquid-liquid interfaces. Bacterial biofilms are often comprised of microcolonies (approximately dome-shaped masses of bacteria and matrix) separated by “voids” through which the medium (e. g. water) may flow relatively uninhibited. The microcolonies may join together above the substratum to form a continuous layer, closing the network of channels separating microcolonies. This structural complexity—combined with observations that oxygen limitation (a ubiquitous challenge for anything growing in size beyond the scale of diffusion) is at least partially eased by movement of medium throughout the biofilm—has lead some to speculate that this may constitute a circulatory system ^[7]. This is an article about the rock music band "Circulatory System"

It is not surprising that many researchers have started calling prokaryotic communities multicellular (for example ^[8]). Differential cell expression, collective behavior, signaling, programmed cell death, and (in some cases) discrete biological dispersal events all seem to point in this direction. Programmed cell-death ( PCD) is death of a cell in any form mediated by an intracellular program Biological dispersal refers to those processes by which a Species maintains ecosystem However, these colonies are seldom if ever founded by a single founder (in the way that animals and plants are founded by single cells), which presents a number of theoretical issues. Most explanations of co-operation and the evolution of multicellularity have focused on high relatedness between members of a group (or colony, or whole organism). Co-operation or co-operative behaviours are terms used to describe Behaviours by Organisms which are beneficial The first Organisms that existed are believed to have been Unicellular. If a copy of a gene is present in all members of a group, behaviors that promote cooperation between members may permit those members to have (on average) greater fitness than a similar group of selfish individuals^[9] (see inclusive fitness and Hamilton's rule). There are a few definitions of Inclusive fitness (IF but one (that according to Oli 2003 is not consistent with W From the time of antiquity field biologists have observed that some organisms tend to exhibit strategies that favor the reproductive success of their relatives even at a cost to their own survival What to make of prokaryotic communities clearly founded by many (most likely unrelated) individuals, yet defined by (apparently) high levels of cooperation, communication, and coordinated behavior?

It is likely that these instances of prokaryotic sociality are the rule rather than the exception, a fact that has serious implications for the way we view prokaryotes in general and the way we deal with them in medicine. Bacterial biofilms may be 100x more resistant to antibiotics than free-living unicells and may be nearly impossible to remove from surfaces once they have colonized^[10]. Other aspects of bacterial cooperation—such as bacterial conjugation and quorum-sensing mediated pathogenicity—present additional challenges to researchers and medical professionals seeking to treat the associated diseases. Bacterial conjugation is the transfer of genetic material between bacteria through direct cell-to-cell contact

Reproduction

Bacteria and archaea reproduce through asexual reproduction, usually by binary fission or budding. Asexual reproduction is a form of reproduction which does not involve Meiosis, Ploidy reduction or Fertilization. Binary fission is the form of Asexual reproduction and Cell division used by Prokaryotic organisms (such as Bacteria or Archea) Budding (also called burgeoning) is the formation of a new Organism by the protrusion of part of another organism Genetic exchange and recombination still occur, but this is a form of horizontal gene transfer and is not a replicative process, simply involving DNA being transferred between two cells, as in bacterial conjugation. Bacterial conjugation is the transfer of genetic material between bacteria through direct cell-to-cell contact

Structure

The sizes of prokaryotes relative to other organisms and biomolecules

Recent research indicates that all prokaryotes actually do have cytoskeletons, albeit more primitive than those of eukaryotes. cytoskeleton (also CSK is a cellular " Scaffolding " or " Skeleton " contained within the Cytoplasm. Besides homologues of actin and tubulin (MreB and FtsZ) the helically arranged building block of the flagellum, flagellin, is one of the most significant cytoskeletal proteins of bacteria as it provides structural backgrounds of chemotaxis, the basic cell physiological response of bacteria. MreB is a protein found in bacteria that has been identified as a homologue of Actin, as indicated by similarities in Tertiary structure and conservation FtsZ is a Protein encoded by the ftsZ Gene that assembles into a ring at the future site of the A flagellum ( plural flagella) is a tail-like structure that projects from the Cell body of certain Prokaryotic and Eukaryotic cells and it Flagellin is a Protein that arranges itself in a hollow cylinder to form the filament in Bacterial Flagellum. Chemotaxis, a kind of Taxis, is the phenomenon in which bodily cells bacteria, and other single-cell or Multicellular organisms direct their movements At least some prokaryotes also contain intracellular structures which can be seen as primitive organelles. Membranous organelles (a. k. a. intracellular membranes) are known in some groups of prokaryotes, such as vacuoles or membrane systems devoted to special metabolic properties, e. g. photosynthesis or chemolithotrophy. Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. A lithotroph is an Organism that uses an Inorganic substrate (usually of mineral origin to obtain reducing equivalents for use in biosynthesis (e Additionally, some species also contain protein-enclosed microcompartments mostly associated with special physiological properties (e. g. carboxysomes or gas vacuoles).

Morphology of prokaryotic cells

Prokaryotic cells have various shapes; the three basic shapes are:^[11]

• Cocci - spherical
• Bacilli - rod shaped
• Spiral - curve (see Bacteria#Morphology)

Environment

Prokaryotes are found in nearly all environments on earth. A flagellum ( plural flagella) is a tail-like structure that projects from the Cell body of certain Prokaryotic and Eukaryotic cells and it The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer A cell wall is a tough flexible and sometimes fairly rigid layer surrounding a cell, located external to the Cell membrane, which provides the cell with structural Mycoplasma is a Genus of bacteria which lack a Cell wall. Without a cell wall they are unaffected by many common Antibiotics such The cytoplasm is the contents of a cell that is enclosed within the Plasma membrane. Ribosomes ( from ribo nucleic acid and "Greek soma ( meaning body") are complexes of RNA and Protein that In Prokaryotes, the nucleoid (meaning nucleus-like) is an irregularly-shaped region within the cell of Prokaryotes where the Genetic material Glycocalyx is a general term referring to extracellular Polymeric material produced by some Bacteria, Epithelia and other cells Inclusions (Cytoplasmic are chemical substances that may or may not be present in a cell depending on the cell type Staphylococcus aureus Gramjpg|thumb|300px| Staphylococcus bacteria]] Cocci (singular - coccus, from the Latin coccinus (scarlet and derived from the Bacilli specifically refers to a taxonomic class of Bacteria. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Archaea in particular seem to thrive in harsh conditions, such as high temperatures (thermophiles) or salinity (halophiles). Organisms such as these are referred to as extremophiles. An extremophile is an Organism that thrives in and may even require Physically or Geochemically extreme conditions that are detrimental to the Many prokaryotes live in or on the bodies of other organisms, including humans.

Evolution of prokaryotes

It is generally accepted that the first living cells were some form of prokaryote and may have developed out of protobionts. In the Natural sciences, Abiogenesis, or origin of life, is the study of how Life on Earth emerged from Inanimate Organic Protobionts are systems that are considered to have possibly been the precursors to Prokaryotic cells A protobiont is an aggregate of abiotically produced organic Fossilized prokaryotes approximately 3. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. 5 billion years old have been discovered (less than 1 billion years after the formation of the earth's crust), and prokaryotes are perhaps the most successful and abundant organism even today. Eukaryotes only formed later, from symbiosis of multiple prokaryote ancestors; their first evidence in the fossil record appears approximately 1. 7 billion years ago, although genetic evidence suggests they could have formed as early as 3 billion years ago. ^[12]

While Earth is the only place in the universe where life is known to exist, some have suggested evidence of life on Mars in the form of fossil or living prokaryotes;^[13][14] this is open to considerable debate and skepticism. Scientists have long speculated about the possibility of life on Mars owing to the planet's proximity and similarity to Earth. ^[15][16]

Prokaryotes diversified greatly throughout their long existence. The metabolism of prokaryotes is far more varied than that of eukaryotes, leading to many highly distinct types of prokaryotes. For example, in addition to using photosynthesis or organic compounds for energy like eukaryotes do, prokaryotes may obtain energy from inorganic chemicals such as hydrogen sulfide. Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. Hydrogen sulfide (or hydrogen sulphide) is the Chemical compound with the formula H 2 S. This has enabled the bacteria to thrive and reproduce. Today, archaebacteria can be found in the cold of Antarctica and in the hot Yellowstone springs. A hot spring is a spring that is produced by the emergence of geothermally heated Groundwater from the earth's crust.

References

See also

• Archaea and Bacteria, the two prokaryotic taxa
• Monera, an obsolete kingdom including both of the above
• Bacterial cell structure
• Nanobe
• Virus
• Prion
• Symbiogenesis

External links

• Prokaryote versus eukaryote, BioMineWiki

This article contains material from the Science Primer published by the NCBI, which, as a U. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Monera are bacteria and other mostly tiny single-celled organisms whose genetic material is loose in the cell In biological Taxonomy, a kingdom or regnum is a Taxonomic rank in either (historically the highest rank or (in the new three-domain system Bacteria, despite their apparent simplicity contain a well developed cell structure which is responsible for many of their unique biological properties Nanobes are tiny filamental Structures first found in some rocks and Sediments Some hypothesize that they are the smallest form of Life A virus (from the Latin virus meaning Toxin or Poison) is a sub-microscopic infectious agent that is unable A prion (ˈpriːɒn is thought to be an infectious agent that according to current scientific consensus is comprised entirely of a propagated, mis-folded Symbiogenesis is the merging of two separate organisms to form a single new organism The National Center for Biotechnology Information ( NCBI) is part of the United States National Library of Medicine (NLM a branch of the National Institutes S. government publication, is in the public domain. The public domain is a range of abstract materials &ndash commonly referred to as Intellectual property &ndash which are not owned or controlled by anyone