Definition, explanation and examples
As prokaryotes (Singular: prokaryote) or prokaryotes are called microorganisms without nucleus. In the systematic classification of the living beings, the two domains of the bacteria and archaea to assign to the prokaryotes. Living organisms with nucleus (eukaryotes) form an independent domain.
Structure of prokaryotes
Whether a living organism is counted among the prokaryotes or eukaryotes depends only on the presence of a nucleus (prokaryotes without nuclei, eukaryotes with nucleus). Furthermore, further distinguishing features of both cell types with regard to their intracellular organization can be observed: Prokaryotic cells, also known as Protocyten designated, as already mentioned have none nucleus, While the nucleus of eukaryotes contains the genetic material, the DNA of the prokaryotes floats freely in the cytoplasm of the cell. This area, where the DNA is located in prokaryotes, is also called nucleoid or nucleoid designated. The core equivalent is analogous to the "real" nucleus of eukaryotes. Both the nuclear equivalent of the prokaryotes and the nucleus of the eukaryotes perform the same functions (control of gene expression -> metabolic processes, cell growth and cytokinesis), but must not be equated with each other.
The genome of most prokaryotes consists of a circularly-arranged, double-stranded piece of DNA. One speaks also of the so-called Bakterienchromosom, In contrast to the genetic material of the eukaryotes, the DNA here has no beginning or end, but forms a self-contained molecular composite. Some prokaryotes also have other DNA molecules in the form of plasmids, These are round, floating in the cytoplasm, DNA molecules with mostly not insignificant genetic information, such as antibiotic or toxin resistance. Plasmids can even be exchanged and spread from bacterium to bacterium.
Outwardly, the prokaryotic cell becomes one cell wall surround. Functionally, the cell wall on the one hand maintains the shape of the protocyte, on the other hand, it also protects against a concentration balance with the environment. Because in the outer environment of the cell there is a much lower concentration of dissolved particles than inside the cell. The osmotic pressure would quickly lead to the inflow of water in a semipermeable membrane. With the result that the cell bursts.
The entire cell is wrapped in addition to the glycocalyx, a mucus layer of polysaccharides to protect against dehydration.
All around the Protocyte can be found with the Pili (Singular: Pilus) Small cell processes that can have very different functions. Depending on the type, a pili can attach to other solids (to stay in a convenient location), nutrients (to absorb food from the environment) or other bacteria (to exchange genes). Not to be confused with the pili, however, is the much larger, and made of proteins flagellum, which only serves for locomotion. To put it simply, the flagellum serves the protocyte as "leg", the pili as "arms" (please do not write in the exam, the comparison is only an illustration!)