The cells of prokaryotic organisms do not have a cell nucleus.
Prokaryote is a notion used in biology to name those organisms that do not have a cell nucleus . Its DNA , therefore, is spread throughout the cytoplasm .
It is possible to differentiate between prokaryotic organisms (also called prokaryotes ) and eukaryotic organisms . In this second group are those organisms whose cells have a nucleus that contains DNA. It is important to highlight, however, that eukaryotic organisms developed through a symbiotic relationship maintained by different types of prokaryotes. In this way, prokaryotes were already present on our planet about 3.5 billion years ago, while eukaryotic organisms only emerged about 1.8 billion years ago.
Characteristics of prokaryotes
At a general level, it can be said that prokaryotes measure between one and seven micrometers. These are microorganisms that reproduce asexually , through a process of binary fission , and that feed as osmotrophs .
Other common characteristics of prokaryotic organisms are the presence of a membrane around the cytoplasm, plasmids and operons. It is worth mentioning that, although the majority of prokaryotes are unicellular, there are also myxobacteria that go through multicellular periods at some point in their life cycle.
As for the main characteristic (the absence of a cell nucleus) of prokaryotes, it arises because their components (from DNA to proteins) are soluble in water . The cell membrane, therefore, provides the corresponding delimitation of the organism in question.
Bacteria are prokaryotes.
Classification according to type
Prokaryotic cells can be classified according to various points of view. According to its morphology, we can talk about:
- Coco : is a morphological class of bacteria. It can be said that its appearance is spherical, since none of its dimensions presents a clear predominance over the others.
- Bacillus : it is a bacteria that looks similar to a rod and can be divided into Gram positive (since it does not have a lipopolysaccharide layer, it fixes gentian violet in the cell wall) and Gram negative (since it does have the lipopolysaccharide layer, it does not sets gentian violet).
- Vibrio : This is a genus of bacteria , several of which are pathogenic and cause disorders of the digestive tract. Such is the case of Vibrio vulnificus (which transmits infections through the consumption of raw fish and shellfish) and Vibrio cholerae (the causative agent of cholera). The genus Vibrio is included in the Proteobacteria, more specifically in the gamma group. Proteobacteria, for their part, are one of the most important groups of bacteria and can be free-living or include pathogens.
- Spiril : this type of prokaryote is a flagellated bacteria that has a spiral or helical appearance and uses viscous media for its movement, which occurs in a screw manner . Since its diameter is not important, it has the possibility of passing through the mucous membranes, as occurs with Treponema pallidum , which causes syphilis in men. Spiril is particularly sensitive to environmental conditions, and this requires direct contact or vector contact for transmission if it is pathogenic.
Taking into account the cell envelope of the prokaryote, it is possible to distinguish between:
- Gracilicutes : They have a double membrane, with a thin wall of peptidoglycan between them. It is seen in Gram negative bacteria.
- Firmicutes : they have a cytoplasmic membrane and a peptidoglycan wall of considerable thickness. An example is found in Gram positive bacteria.
- Mendosicutes : has a cell wall composed mostly of glycopeptides and a plasma membrane in which glycerols and lipids are linked with ether bonds, unlike what occurs in bacteria, where the bonds are ester.