User:Bomber1705/Prokaryotic cell



It is called prokaryote to cells without a defined cell nucleus, whose genetic material is dispersed in the cytoplasm, assembled in a zone called nucleoid. In contrast, cells that do have a differentiated nucleus of the cytoplasm are called eukaryotes, ie those whose DNA is inside a compartment separated from the rest of the cell.

In addition, the term prokaryotic refers to organisms belonging to the Prokaryota empire, whose concept coincides with the Monera kingdom of the classifications of Herbert Copeland or Robert Whittaker which, although earlier, still remain popular.

Almost without exception, organisms based on prokaryotic cells are unicellular (organisms consisting of a single cell).

It is believed that all organisms that currently exist derive from a prokaryotic unicellular form (LUCA). There is a theory, serial endosymbiosis, which considers that throughout a slow evolutionary process, about 1500 million years ago, the prokaryotes became more complex beings by symbiotic association: eukaryotes.

Cell Structure
The basic prokaryotic cell structure has the following components: Additionally there may also be: For comparison with the prokaryotic cell, see Comparative Table.
 * Plasmatic membrane
 * Cell wall (except mycoplasmas and thermoplasm)
 * Cytoplasm
 * Nucleoid
 * Ribosomes
 * Prokaryotic compartments. Compartments have been identified that appear to have the purpose of safeguarding or performing certain types of specialized tasks. Some of them are Chlorosomes, Carboxysomas, Anammoxosomas, Phycobilisomas, Proteosomes and Magnetosomas.
 * Scourge (s)
 * External membrane (in Gram negative bacteria)
 * Periplasm
 * Capsule
 * Cytoplasmic inclusions (nutrients and gas vesicles)
 * Pili o fimbrias
 * Glycocalyx
 * Biofilm
 * Cover S
 * Formation of spores.
 * Plasmids
 * Mesosoma

Biochemical and metabolic diversity
Since its inception, they have undergone great diversification. The metabolism of prokaryotes is enormously varied (unlike eukaryotes), and causes some prokaryotes to be very different from others. Some are very resistant to extreme environmental conditions like temperature or acidity, they are called Extremophiles.

The entire diversity of metabolic systems is encompassed by prokaryotes, so the metabolic diversity of eukaryotes is considered as a subset of the former.

Nutrition
Nutrition can be autotrophic (chemosynthesis or photosynthesis) or heterotrophic (saprophytic, parasitic or symbiotic). In terms of metabolism organisms can be: strict or facultative anaerobes, or aerobic.
 * Chemosynthesis is the biological conversion of molecules of a carbon and nutrients into organic matter using the oxidation of inorganic molecules as an energy source, without the use of sunlight, as opposed to photosynthesis. A large proportion of living organisms base their existence on chemosynthetic production on thermal faults, cold strains or other extreme habitats to which sunlight is unable to reach.

The organisms capable of carrying out this process are called phottrophs and if they are also able to fix the atmospheric CO2 (which happens almost always) are called autotrophs. Except in some bacteria, the release of molecular oxygen (from water molecules) into the atmosphere (oxygen photosynthesis) occurs in the photosynthesis process.
 * Photosynthesis is the basis of our present life on Earth. It consists of a series of processes by which plants, algae and some bacteria capture and use the energy of light to transform the inorganic matter from their external environment into organic matter that they use for their growth and development.

It is widely accepted that the present oxygen content in the atmosphere has been generated from the appearance and activity of these photosynthetic organisms. This has allowed the evolutionary appearance and development of aerobic organisms capable of maintaining a high metabolic rate (aerobic metabolism is very energy efficient).

The other mode of photosynthesis, anoxigenic photosynthesis, in which oxygen is not released, is carried out by a reduced number of bacteria, such as purple sulfur bacteria and green sulfur bacteria; These bacteria use H2S as the hydrogen donor, releasing sulfur.
 * Saprophytic nutrition: based on the remains of living beings, from which it produces decomposition.
 * Parasitic nutrition: they obtain the food of a host that they harm but do not get to kill.
 * Nutrición simbiótica:The beings that perform the symbiosis obtain organic matter from another living being, which also benefits.

Reproduction
It occurs in two ways: asexual reproduction or parasexual
 * Asexual reproduction by bipartition or binary fission: it is the simplest and fastest form in unicellular organisms, each cell is divided in two, previous division of the genetic material and later division of cytoplasm (cytokinesis).


 * Parasexual reproduction, to obtain variability and adapt to different environments, between the bacteria can occur exchange of DNA such as conjugation, transduction and transformation.
 * Conjugation: A process that occurs when a bacterium makes contact with another using a thread called Pili. The moment the cytoplasm is connected, the individual donor (considered as masculine) transfers part of its DNA to another receptor (considered as feminine) that incorporates it (through the Pili) to its genetic endowment by recombination and transmits it in turn when reproducing.
 * Transduction: In this process, a transmitting agent, which is usually a virus, carries DNA fragments of a bacterium parasitized to another new receptor, so that the DNA of the parasitized bacterium is integrated into the DNA of the new bacterium.
 * Transformation: A bacterium can introduce in its interior DNA fragments that are free in the middle (plasmides). These may come from the breakdown or degradation of other bacteria around them.

According to its morphology
In other cases, especially in archaea, you can find a varied morphology, which includes pleomorphic forms (changing forms), irregular, lobed, flat, rectangular or square like Haloquadratum.
 * Coco is a morphological type of bacterium. It has a more or less spherical shape (none of its dimensions clearly dominates the others).
 * Bacilli are bacteria that have a cane shape, when they are observed under the microscope. Bacilli are usually divided into:
 * Gram-positive Bacilli: They set the gentian Violet (gram stain) on the cell wall because they lack a layer of lipopolysaccharides.
 * Gram negative Bacilli: They do not fix gentian Violet because they possess the lipopolysaccharide layer.
 * Vibrio is a genus of bacteria, included in the Gamma group of the Proteobacteria. Several of the species of Vibrio are pathogenic, causing diseases of the digestive tract, especially Vibrio cholerae, the agent that provokes cholera, and Vibrio vulnificus, which is transmitted through the ingestion of shellfish.
 * Dysentery are either helically or spirally whipped bacteria. They move in viscous media advancing in screw. Its diameter is very small, which makes it possible to penetrate the mucous membranes; For example Treponema pallidum that produces syphilis in man. They are more sensitive to the environmental conditions than other bacteria, so when they are pathogenic they are transmitted by direct contact (sexual way) or by vectors, normally arthropods blood

Según la envoltura celular
Depending on the type of cell wall and the number of membranes, there may be the following types of prokaryotes cells:
 * (a) Gracilicutes (= thin skin), characteristic of Gram-negative bacteria, which are didermal, ie double membrane and between these membranes a thin wall of peptidoglycan
 * (b) Firmicutes (= strong skin), own of Gram-positive bacteria, with a cytoplasmic membrane and a thick wall of peptidoglycan
 * (c) Mendosicutes (= rare skin), characteristic of Archaea, with a cell wall mostly glycopeptides different from that of the bacteria. The plasma membrane is equally different, since lipids are join to glycerol with ether links, instead of ester bonds as in bacteria
 * (d) Tenericutes (= delicate skin), characteristic of Mycoplasma, endoparasitic bacteria that lack cell wall, apparently as an evolutionary adaptation to the intracellular habitat

Clasificación biológica
According to the three-domain system the main prokaryotes groups are archaea and bacterium. The most important difference in the onset of the difference between these two groups is in the sequence of nitrogenous bases of the fractions of ribosomal 16s RNA.
 * Archaea are very primitive unicellular microorganisms. Like bacteria, archaea lack nucleus and are therefore prokaryotes. However, differences in the molecular level between archaea and bacteria are so fundamental that they are classified in different groups. In fact, these differences are greater than there are, for example, between a plant and an animal. Archaea are now considered to be phylogenetically closer to eukaryotes than to bacteria. The archaea were originally discovered in extreme environments, but since then they have been found in all types of habitats.
 * Methanogens are prokaryotes microorganisms that live in strictly anaerobic media and obtain energy through the production of natural gas, methane (CH4). Thanks to this characteristic, this type of organism has a great ecological importance, since it intervenes in the degradation of the organic matter in the nature, and in the cycle of the carbon. In addition, they are a phylogenetically heterogeneous group where the common factor that unites them is the production of methane gas and its unique cofactors. We can find them in our gut.
 * Halophilic: They live in extremely saline environments. Halococcus and Halobacterium only live in media with more than 12% of salt (much more savoury than sea water). The
 * Hipertermófilas live and develop in extreme temperatures and ph extremes in sites with volcanic activity (such as geysers) on the oceanic ridges, where most living beings would be unable to survive. There is a theory that they were possibly the first simple cells.


 * Bacteria are microscopic organisms formed by more evolved prokaryotes cells. Cyanobacteria, also known as green algae, are photosynthetic and colonial eubacteria that have been living on our planet for more than 3 billion years. This bacterium grows on mats and mounds in the shallowest parts of the ocean. Today there are only in some regions, but billions of years ago there were in such a large number, that they were able to add, through photosynthesis, enough oxygen to the primitive atmosphere of the Earth, so that the animals that needed oxygen could survive.