Prokaryotic cell

A prokaryotic cell or prokaryote is a unicellular organism, whose genetic material is dispersed in the cytoplasm, gathered in an area called a nucleoid. Cells that do have a nucleus differentiated from the cytoplasm are called eukaryotes, that is, those in which their DNA is found within a separate compartment from the rest of the cell.

Cell structure of a bacterium, typical procarote cell.

In addition, the term prokaryote refers to organisms belonging to the Prokaryota domain, whose concept coincides with the Monera kingdom of the classifications of Herbert Copeland or Robert Whittaker that, although earlier, are still popular.

Almost without exception, organisms based on prokaryotic cells are unicellular.

All organisms in existence today are believed to derive from a single-celled prokaryotic (LUCA) form.

There is a theory, called serial endosymbiosis, which considers that through a slow evolutionary process, around 2.3 billion years ago, prokaryotes evolved into more complex beings by symbiotic association: eukaryotes.

Cell structure

The basic prokaryotic cell structure has the following components:

• Cell membrane
• Cell Pared (except in mycoplasms and thermoplasmates)
• Cytoplasma
• Nucleoid
• Ribosomes
• Procariot compartments. compartments that appear to have the purpose of safeguarding or carrying out certain types of specialized tasks have been identified. Some of them are Clorosomas, Carboxisomas, Anammoxosomes, Ficobilisomas, Proteosomes and Magnetosomes.

Additionally there may also be:

• Flagelo(s)
• External membrane (in negative Gram bacteria)
• Periplasma.
• Capsuula
• Cytoplasmic (nutrients and gallbladders)
• Pili or fimbrias
• Glycoalix
• Biofilm
• Capa S
• Spores training.
• Plásmidos
• Mesosoma

For its comparison with the eukaryotic cell, see the Comparative Table.

Biochemical and metabolic diversity

Since their appearance, they have undergone great diversification. The metabolism of prokaryotes is enormously varied (unlike eukaryotes), causing some prokaryotes to be very different from others. Some are very resistant to extreme environmental conditions such as temperature or acidity, they are called Extremophiles.

Nutrition

Nutrition can be autotrophic (chemosynthesis or photosynthesis) or heterotrophic (saprophytic, parasitic, or symbiotic). Regarding metabolism, organisms can be: strict or facultative anaerobes, or aerobic.

• La quimiosynthesis is the biological conversion of molecules of a carbon and nutrients in organic matter using the oxidation of inorganic molecules as a source of energy, without the use of sunlight, unlike photosynthesis. A large part of the living organisms base their existence on the chemistintic production in thermal failures, cold strains or other extreme habitats to which the sunlight is incapable of arriving.

• La photosynthesis is the basis of the present life on Earth. It consists of a series of processes through which plants, algae and some bacteria capture and use the energy of light to transform the inorganic matter of their external environment into organic matter that they use for their growth and development.

The organisms capable of carrying out this process are called phototrophs and if they are also capable of fixing atmospheric CO2 (which almost always happens) they are called autotrophs. Except in some bacteria, the release of photosynthesis occurs of molecular oxygen (from water molecules) into the atmosphere (oxygenic photosynthesis).

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

The other form of photosynthesis, anoxygenic 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 a hydrogen donor, thereby releasing sulfur.

• Nutrition saprofita: based on remains of living beings, of which decomposition produces.
• Parasitic nutrition: they get the food from a host they hurt but they don't get to kill.
• Symbiotic nutrition: beings who perform symbiosis get the organic matter from another living being, which also benefits.

Playback

It occurs in two ways: asexual reproduction or parasexual reproduction

• Reproduction asexual by bipartition or binary fission: it is the easiest and fastest form in unicellular organisms, each cell is divided into two, after division of genetic material and subsequent division of cytoplasm (cythokinis).

• Parasexual reproduction, to obtain variability and adapt to different environments, among bacteria, DNA exchange can occur such as conjugation, transduction and transformation.
• Conjugation: Process that occurs when one bacteria makes contact with another using a thread called PILI. At the time when cytoplasms are connected, the donor individual (considered as male) transfers part of his DNA to another receptor (considered as female) that incorporates it (through PILI) into its genetic strength by recombination and transmits it in turn when reproduced.
• Translating: In this process, a transmitter agent, which is usually a virus, carries DNA fragments from a bacteria parasitized to another new receptor, so that the DNA of the parasitic bacteria is integrated into the DNA of the new bacteria.
• Transformation: A bacteria can enter inside DNA fragments that are free in the middle (plsmids). These may come from the breakdown or degradation of other bacteria around them.

Prokaryotic Cell Types

According to its morphology

From left to right: Cocos, spirilos and bacilos.

• Coco It's a morphological type of bacteria. It has more or less spherical shape (no one of its dimensions is clearly predominant over the others).
• Them Bacilos They are bacteria that have a cane shape, when seen under a microscope. The bats are usually divided into:
  • Positive Gram Bacilos: they fix the genciana violet (Gram stain) on the cell wall because they lack a layer of lipopolisaccharides.
  • Negative Gram Bacilos: do not fix the genciana violet because they have the lipopolisaccharide layer.
• Vibrio is a genus of bacteria, including in the gamma group of proteobacteries. Several species Vibrio are pathogens, causing diseases of the digestive tract, especially Vibrio cholerae, the agent that causes cholera, and Vibrio vulnificus, which is transmitted through seafood intake.
• Them spirilos are helically or spirally flagged bacteria. They move in viscous media moving in screw. Its diameter is very small, which makes them able to pass through the mucosas; for example Treponema pallidum that produces syphilis in man. They are more sensitive to environmental conditions than other bacteria, so when they are pathogens they are transmitted by direct contact (sexual) or by means of vectors, usually hematophagus arthropods

In other cases, especially in archaea, a varied morphology can be found, including pleomorphic (changeable shapes), irregular, lobed, flat, rectangular, or square forms such as Haloquadratum.

According to the cell envelope

Types of procariot according to their cellular wrap. A: bacteria Negative Gram, B: bacteria Positive Gram, C: arquea, D: micoplasma. 1- cytoplasmic membrane, 2- bacterial cell wall, 3- periplasmic space, 4- outer membrane, 5- archaic cell wall.

Depending on the type of cell wall and the number of membranes, there may be the following types of prokaryotic cells:

• A) Gracilicutes (= thin skin), characteristic of the negative gram bacteria, which are didérmicas, that is, of double membrane and between these membranes a thin wall of peptidoglycan
• B) Firmicutes (=strong skin), characteristic of positive gram bacteria, with a cytoplasmic membrane and a thick glycan peptido wall
• C) Mendosicutes (=rare skin), typical of arches, with a cellular wall mostly of glycopeptides different from that of bacteria. Plasmatic membrane is equally different, as lipids bind to glycerols with ether links, instead of sterling links as in bacteria
• D) Tenericutes (= delicate skin), typical of mycoplasms, endoparásite bacteria that lack cellular wall, apparently as an evolutionary adaptation to intracellular habitat

Biological classification

Philogenetic tree of living organisms, which shows the origins of eukaryotes and prokaryota

According to the three-domain system, the main prokaryotic groups are Archaea and Bacteria. The most important difference that initially supported the difference between these two groups is in the sequence of nitrogenous bases of the 16S ribosomal RNA fractions.

• Archaees are very primitive unicellular microorganisms. Like bacteria, archaea lacks nucleus and are therefore procarious. However, differences at the molecular level between archaea and bacteria are so fundamental that they are classified into different groups. In fact, these differences are greater than there are, for example, between a plant and an animal. Archaea is currently considered to be more phylogenically close to eukaryants than to bacteria. Archaea were originally discovered in extreme environments (such as in oceanic pits or in salt-rich waters), but has since been found in all types of habitats.
  • Metanogens they are procarious microorganisms that live in strictly anaerobic means and that obtain energy through the production of natural gas, methane (CH4). Thanks to this characteristic, this type of organism is of great ecological importance, as it intervenes in the degradation of organic matter in nature, and in the carbon cycle. In addition, they are a philosophically 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 intestine.
  • Halophiles: They live in extremely salty environments. Halococcus and Halobacterium only live in media with more than 12% salt (much more salty than seawater).
  • The hyperthermophileslive and develop in conditions of extreme temperatures and extreme pH in places with volcanic activity (such as geysers) in oceanic dorsals, 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 procarote cells. The cyanobacteria, also known as algae greenazules, are ancient and colonial photos that have been living on our planet for more than 3 billion years. This bacteria grows in mats and mounds in the less deep parts of the ocean. Today there are only those in some regions, but thousands of years ago they 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.