Prokaryote

Most are unicellular, but a few prokaryotes such as myxobacteria have multicellular stages in their life cycles.[1]

Prokaryotic cell Structure
Flagellum
Cell membrane
Cell wall (except genus Mycoplasma)
Cytoplasm
Ribosome
Nucleoid
Glycocalyx
Inclusions
Morphology of prokaryotic cells

Prokaryotic cells have various shapes; the four basic shapes are:[15]

* Cocci - spherical
* Bacilli - rod shaped
* Spirochaete - spiral shaped
* Vibrio - comma shaped

Environment

Prokaryotes live in nearly all environments on earth where there is liquid water.

A distinction between prokaryotes and eukaryotes (meaning true kernel, also spelled "eucaryotes") is that eukaryotes do have "true" nuclei containing their DNA. Unlike prokaryotes, eukaryotic organisms may be unicellular, as in amoebae, or multicellular, as in plants and animals.

Instead processes such as oxidative phosphorylation and photosynthesis take place across the prokaryotic plasma membrane.[5]

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.

Also the size of Ribosomes in prokaryotes are smaller than in eukaryotes, which is now where respiration takes place.[citation needed] The genomes of prokaryotes are held within an irregular DNA/protein complex in the cytosol called the nucleoid, which lacks a nuclear envelope.[4]

However, prokaryotes do possess some internal structures, such as cytoskeletons,[6][7] and the bacterial order Planctomycetes have a membrane around their nucleoid and contain other membrane-bound cellular structures.[8]

A distinction between prokaryotes and eukaryotes (meaning true kernel, also spelled "eucaryotes") is that eukaryotes do have "true" nuclei containing their DNA. Unlike prokaryotes, eukaryotic organisms may be unicellular, as in amoebae, or multicellular, as in plants and animals.

Cells in biofilms often show distinct patterns of gene expression (phenotypic differentiation) in time and space.

At least some prokaryotes also contain intracellular structures which can be seen as primitive organelles.

Most are unicellular, but a few prokaryotes such as myxobacteria have multicellular stages in their life cycles.[1]

Instead processes such as oxidative phosphorylation and photosynthesis take place across the prokaryotic plasma membrane.[5]

The prokaryotes (pronounced /proʊˈkæri.oʊts/ or /proʊˈkæriəts/) are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles.

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.

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.

Cells in biofilms often show distinct patterns of gene expression (phenotypic differentiation) in time and space.

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).

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.[2]

Differential cell expression, collective behavior, signaling, programmed cell death, and (in some cases) discrete biological dispersal events all seem to point in this direction.

Reproduction

Bacteria and archaea reproduce through asexual reproduction, usually by binary fission or budding.

Prokaryotic cell Structure
Flagellum
Cell membrane
Cell wall (except genus Mycoplasma)
Cytoplasm
Ribosome
Nucleoid
Glycocalyx
Inclusions
Morphology of prokaryotic cells

Prokaryotic cells have various shapes; the four basic shapes are:[15]

* Cocci - spherical
* Bacilli - rod shaped
* Spirochaete - spiral shaped
* Vibrio - comma shaped

Environment

Prokaryotes live in nearly all environments on earth where there is liquid water.

For example, in addition to using photosynthesis or organic compounds for energy, as eukaryotes do, prokaryotes may obtain energy from inorganic compounds such as hydrogen sulfide.

In other words neither their DNA, nor any of their other sites of metabolic activity, are collected together in a discrete membrane enclosed area.

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.

The oldest known fossilized prokaryotes were laid down approximately 3.5 billion years ago, only about 1 billion years after the formation of the Earth's crust.

Also, like multicellular eukaryotes, these changes in expression appear to often result from cell-to-cell signaling, a phenomenon known as quorum sensing.

Current opinions on the origin and position of eukaryotes span a broad spectrum including the views that eukaryotes arose first in evolution and that prokaryotes descend from them, that eukaryotes arose contemporaneously with eubacteria and archeabacteria and hence represent a primary line of descent of equal age and rank as the prokaryotes, that eukaryotes arose through a symbiotic event entailing an endosymbiotic origin of the nucleus, that eukaryotes arose without endosymbiosis, an...

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.

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.

This enables prokaryotes to thrive in harsh environments as cold as the snow surface of Antarctica, and as hot as undersea hydrothermal vents and land-based hot springs.