What is a prokaryotic cell?
We explain what a prokaryotic cell is, how it is classified and the parts that compose it. Its functions and what a eukaryotic cell is.
Prokaryotes are evolutionarily prior to eukaryotes.
Prokaryota or prokaryote cells are unicellular living organisms, belonging to the Prokaryota empire or Monera kingdom, depending on the biological classification preferred.
These cells are characterized by not having a cell nucleus, but having their genetic material dispersed in the cytoplasm, scarcely gathered in an area called the nucleoid.
Prokaryotic organisms are evolutionarily prior to eukaryotic organisms, i.e., those with a nucleus. The simplest life forms were and still are prokaryotes, like bacteria and arches.
This simplicity has allowed its great diversification, which translates into extremely diverse metabolisms (not the same with eukaryotes) and an enormous diversity in terms of environment, nutrition or even structure.
Thus, prokaryotic cells can be either autotrophic (making their own food) or heterotrophic (feeding on foreign organic matter), both aerobic (requiring oxygen) and anaerobic (not requiring oxygen), which translates into various nutrition mechanisms:
- Photosynthesis. Like plants, some prokaryotes can synthesize chemical energy from sunlight, both in the presence and absence of oxygen.
- Chemosynthesis. Similar to photosynthesis, cells undertake the oxidation of inorganic matter as a mechanism to obtain their energy and obtain their own organic matter to grow.
- Saprophytic nutrition. Based on the decomposition of organic matter left by other living beings, either when they die or as remains of their own food.
- Symbiotic nutrition. Some prokaryotes obtain their organic matter to exist from other living beings, generating a benefit and therefore collaborating to exist.
- Parasitic nutrition. The opposite of symbiotics: the organism is nourished from the organic matter of a larger one, which it harms in the process even if it does not kill it directly.
Finally, the reproduction of prokaryotic cells also tends to be very varied, both asexual (mitosis) and parasexual (conjugation, transduction and transformation of DNA for adaptive purposes).
Prokaryotic cell types
Coconut bacteria are more or less spherical and uniform in shape.
Prokaryotic cells can be of four types, according to their morphology:
- Coconut. A typical morphological type of bacteria, more or less spherical and uniform.
- Bacillus. Stick-shaped, they include a vast range of bacteria and other saprophytic organisms of free life.
- Vibrio. A genus of proteobacteria responsible for most infectious diseases in humans and higher animals, especially those typical of the digestive tract, such as cholera.
- Spirils. They have a helical or spiral shape, are usually very small and range from pathogenic bacteria to autotrophs.
- Pleomorphic. That is to say, in a changing way, mainly referring to the archeas.
- Rectangular. Also typical of archeological forms such as the Haloquadratum.
Parts and functions of a prokaryote cell
The prokaryotic cell usually has the following structures:
- Plasma membrane. That border that divides the inside and outside of the cell, in turn serving as a filter to allow the entry of nutrients or the exit of waste.
- Cell wall. A trait shared with vegetables and fungi consists of a strong, rigid fibre that gives the cell a definite shape and an additional layer of protection.
- Cytoplasm. The very inside of the cell, i.e. a very fine colloidal substance that makes up the cell “body”.
- Nucleoid. Without becoming a nucleus, but a very dispersed region, it is the part of the cytoplasm where the genetic material is usually found within the prokaryotic cell. This genetic material is obviously indispensable for reproduction.
- Ribosomes. A complex of proteins and pieces of RNA present in all cells (except sperm), and allow the expression and translation of genetic information, that is, synthesize the proteins required by the cell in its various biological processes, as stipulated in the DNA.
- Compartments prokaryotes. Exclusive to this cellular type, they vary according to the type of organism and have very specific functions within their metabolism. Some examples are: chlorosomes (for photosynthesis), carboxisomes (to fix CO2), ficobilisomas (molecular pigments to collect sunlight), magnetosomes (allow orientation according to the Earth’s magnetic field), etc.
Additionally, these cells may present:
- Flagel. An organism used to mobilize the cell, in the form of a propellant tail.
- External membrane. An additional cell barrier that characterizes gram-negative bacteria.
- Periplasma. A space that surrounds the cytoplasm and separates it from the external membranes, thus allowing greater effectiveness in different types of energy exchange.
- Plasmids. Non-chromosomal, circular forms of DNA, which in certain bacteria accompany the bacterial DNA and are replicated independently, giving it essential characteristics for greater adaptability to the environment.
Eukaryotic cells are distinguished from prokaryotic cells in that they have a nucleus defined in their cytoplasm, where all the DNA of the cell is contained.
This difference seems subtle but underpins a gigantic change in reproduction and other vital processes that led to a higher level of cellular complexity, without which multicellular beings could not have been gestated.