A prokaryotic cell is a unicellular entity whose particularity is that it does not have a differentiated nucleus, and that is the reason why it is called a prokaryotic cell, unlike eukaryotic cells that have their DNA differentiated in the nucleus, and if you want to know what its parts are, you should read this article.
Prokaryotic cell
The prokaryotic cell is the most basic cell in the tree of life. Since it lacks a nucleus, it is called a prokaryote, a term derived from the combination of two Greek words: "pro," meaning prior or before; and "karyon," meaning nut or nucleus. Therefore, the name prokaryote literally means before or prior to the nucleus, and it can be related to the Origin of Life.
Prokaryotic organisms are classified into two levels that have been called domains and are:
- Bacteria Domain: which includes not only bacteria, but also cyanobacteria and mycoplasmas.
- Archaeal DomainArchaea such as thermococci, methanococci, and halobacteria are found in this domain.
Prokaryotic cells can be found almost anywhere in the Earth's biosphere; in fact, they are the only beings that manage to live in the most extreme habitats, such as those with high concentrations of salt or extreme temperatures where they are found. But the most amazing thing is that they can also be found inside the human body, either in the digestive system and on the skin.
Parts of the Prokaryotic Cell and their Functions
Prokaryotic cells are made up of the following parts:
- Cellular membrane.
- Cytoplasm
- Genetic material.
- Cellular wall.
Cellular membrane
The cell membrane has a composition of phospholipids and proteins in different proportions. In the Archaea domain, the archaea, the cell membrane may be made up of a single layer instead of a double layer, as in bacteria and eukaryotic cells.
The function of this membrane, which is called cytoplasmic, is to retain the aggregates inside the prokaryotic cell to cause the enzymatic reactions that catalyze the chemical reactions that archaea and bacteria require to live.
Cytoplasm
The cytoplasm of prokaryotic cells is what is surrounded by the plasma membrane. In the cytoplasm we can find the ribosomes, which are required to synthesize proteins and the nucleoid.
Genetic material
The genetic material, or genome, found in prokaryotic cells consists of a single DNA molecule , enclosed in a simple, round structure and contained within a region of the cytoplasm called the nucleoid. Unlike eukaryotic cells, the DNA in prokaryotic cells is not enclosed within a nuclear membrane. However, in many prokaryotic cells, a small, rounded DNA molecule called a plasmid can also be found in the cytoplasm.
Cellular wall
The cell wall of the prokaryotic cell is an external protective device found in the cell membrane. In bacteria it is made up of peptidoglycan, which is a mesh of polysaccharide chains that are linked with peptides. In archaea, the cell wall is composed of a pseudopeptidoglycan.
cell wall functions
The cell wall performs the following functions in a prokaryotic cell:
- Provides structural rigidity.
- Determine the shape of the prokaryotic cell
- Avoid dehydration.
accessory structures in prokaryotic cells
Prokaryotic cells have three attached structures, which are:
- Capsule: it is a structure found on the surface that looks like a sticky layer, made up of polysaccharides, which are carbohydrate chains. It can be found in multiple bacteria.
- Flagellum: is an appendage used for scrolling.
- Fimbria or pili: they are small appendages found on the surface of bacteria, formed by a protein called fimbrilin or pilin. It can be 3 to 25 nm in diameter and 10 to 20 nm in extent. They are used to be able to adhere to cells and mucosal surfaces and to exchange genetic material during a bond.
Characteristics of the prokaryotic cell
Unlike animal cells , the characteristics of a prokaryotic cell are as follows:
- Shape: there is no uniformity in their representation, so they can be found cylindrical in the case of bacilli, spherical as in cocci, spiral and comma-shaped in the case of vibrios.
- Size: can be between 0,2 to 2 um in terms of diameter and 1 to 6 um in terms of length.
- Regional: it is not a constant characteristic either, because they can be found in isolation or in groups forming what has been called a colony.
- Mobility: if they have flahelos and cilos, then the prokaryotic cells can have displacement.
- Distribution: They are widespread in all areas of the Earth, even in those places that can be considered extreme.
- Metabolism: they can be autotrophic, in the event that they are capable of obtaining energy only from light or from other simple compounds; or they can be heterotrophic, which are those that take energy from external sources.
- membranous intracellular organelles: prokaryotic cells do not have them, they do not even have a nucleus.
- Breathing: can be both aerobic and anaerobic.
most popular prokaryotic cells
The best known and most widespread of the prokaryotic cells are probably Escherichia coli, Vibrio cholerae, Nisseria meningitidis and the cheese bacterium, and in the next section of this article we are going to explain them:
Escherichia coli is possibly the most popular and most common bacterium in clinical laboratories. It is a gram-negative bacillus whose habitat is the gastrointestinal system of animals that can cause infectious ailments such as gastroenteritis and urinary tract infections. E. coli is used in molecular biology and recombinant protein breeding because it is very easy for them to reproduce in culture media.
Vibrio cholerae is classified as a pathogenic agent that causes the very serious disease that is cholera, a gastrointestinal disease that has proven to be very serious for humans. Its peculiarity is that it has a curved morphology, being able to resemble a comma, and they have an external structure called a flagellum thanks to which it can move in the middle of the waters that are contaminated.
Neisseria meningitidis is the pathogen that causes bacterial meningitis disease. Its peculiarity is that it is a gram-negative coccus that usually appears in pairs and has a shape that is similar to a coffee bean, although it is also common for them to appear intertwined in short chains. Their habitat is on the mucosal surfaces of animals that can maintain temperature.
Cheese bacteria, as its name indicates, is found in cheese, which is a food that humans have used in their diet since time immemorial. In order to produce the cheese that is consumed, it is necessary to combine a number of bacteria, including Lactobacillus casei, L. paracasei, L. rhamnosus and L. plantarum.
