Prokaryotic Cell (Meaning and Explanation)

We explain what a prokaryotic cell is, the parts that make it up and their functions. Also how it differs from a eukaryotic cell.

What is a prokaryotic cell?

Prokaryotic or prokaryotic cells form single-celled living organisms belonging to the superkingdom or empire Prokaryota or to the domains Archaea and Bacteria, depending on the biological classification preferred.

The main characteristic of prokaryotic cells is that do not have a membrane that delimits the cell nucleus and, on the other hand, they present their genetic material dispersed in the cytoplasm, barely gathered in an area called the nucleoid.

Prokaryotic organisms (pro- means “before” and karyo which refers to “core”) are evolutionarily older than eukaryotes that is, those that do have a cell nucleus. Although prokaryotic cells emerged in the very distant past, that does not mean that they have disappeared from Earth. In fact, the simplest forms of life are still prokaryotic organisms, such as bacteria and archaea.

This simplicity that characterizes prokaryotic organisms has allowed their great diversification, which translates into extremely diverse metabolisms (the same does not occur with eukaryotes) and enormous diversity in terms of adaptation to different environments, types of nutrition or even cellular structure.

Nutrition mechanisms

prokaryotic cells they can be autotrophic (they make their own food) or heterotrophic (they feed on organic matter produced by another living being), both aerobic (they require oxygen to live) and anaerobic (they do not require oxygen to live), which translates into several nutrition mechanisms:

Photosynthesis. Like plants, some prokaryotes can use the energy of sunlight to synthesize organic matter from inorganic matter, both in the presence and absence of oxygen. There are two types of photosynthesis: oxygenic photosynthesis (which produces oxygen) and anoxygenic photosynthesis (does not produce 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. Chemosynthesis differs from photosynthesis in that the latter uses sunlight as an energy source.
Saprophytic nutrition. It is 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 associate with other living beings, obtain their organic matter to exist from them and a mutual benefit is generated.
Parasitic nutrition. There are prokaryotic organisms (parasites) that feed on the organic matter of another organism (host), which they harm in the process (although they do not kill it directly).

You may be interested: Unicellular Organisms

Finally, The reproduction of prokaryotic cells can be of two types: asexual (through the mechanism of mitosis) or parasexual (three processes related to the exchange and incorporation of changes in the genetic material are involved: conjugation, transduction and transformation of DNA).

Types of prokaryotic cell

Coconut bacteria — Coccus bacteria have a more or less spherical and uniform shape.

Prokaryotic cells can have very varied shapes and often even the same species can adopt changing forms which is called pleomorphism. However, three main types of morphology can be distinguished:

Coconut. It is a typical morphological type of bacteria, which has a more or less spherical and uniform shape. Bacteria can also occur in cocci in groups of two (diplococcus), cocci in groups of four (tetracoccus), cocci in chains (streptococcus), and cocci in irregular groupings or clusters (staphylococcus). For example: Streptococcus pneumoniae, one of the causative agents of bacterial pneumonia.
Bacillus. Rod-shaped with rounded ends, it includes a vast range of bacteria and other free-living saprophytic organisms. Bacilli can also be found in groups of two or forming filaments. For example: Escherichia coli and Clostridium botulinum.
Spirilo. With a helical shape, they are usually very small and range from pathogenic to autotrophic bacteria. For example: species of the genus Campylobacter, such as Campylobacter jejuni, a foodborne pathogen that causes campylobacteriosis.
Spirochaete. They also have helical shapes but are very elongated and flexible. For example: the species of the genus Leptospira that cause leptospirosis.
Vibrios. They are comma-shaped canes. This group includes those of the Vibrio type, a genus of proteobacteria responsible for most infectious diseases in humans and higher animals, especially those typical of the digestive tract. The best known is Vibrio cholerae, the causative agent of cholera.
Some variants of these forms They are coccobacilli (oval) and coryneform bacteria, irregular bacilli with a widened end.

Parts and functions of a prokaryotic cell

The prokaryotic cell has the following structures:

plasma membrane. It is the border that divides the interior and exterior of the cell and serves as a filter to allow the entry and/or exit of substances (such as the incorporation of nutrients or the exit of waste).
cell wall. It consists of a resistant and rigid layer that is located outside the cell membrane, which gives the cell a defined shape and an additional layer of protection. The presence of a cell wall is a trait shared between plants, algae and fungi, although the composition of this cellular structure is different in each of these groups of organisms.
Cytoplasm. It is a very fine colloidal substance that makes up the cell “body” and is found inside the cell.
Nucleoids. It is not a nucleus, it is a very dispersed region that is part of the cytoplasm, where a single circular DNA molecule is usually found that can be associated with a small amount of RNA and non-histone proteins. This DNA molecule is essential for reproduction.
Ribosomes. They are complexes of proteins and pieces of RNA that allow the expression and translation of genetic information, that is, they synthesize the proteins required by the cell in its various biological processes, in accordance with what is stipulated in the DNA.
Prokaryotic compartments. They are exclusive to prokaryotic cells. They vary depending on the type of organism and have very specific functions within its metabolism. Some examples are: chlorosomes (necessary for photosynthesis), carboxysomes (to fix carbon dioxide (CO₂), phycobilisomes (molecular pigments to collect sunlight), magnetosomes (allow orientation according to the Earth's magnetic field), etc.

eukaryotic cell

Eukaryotic cells are distinguished from prokaryotic cells in that have a defined nucleus in their cytoplasm (where most of the cell's DNA is contained) and in which they have the presence of membranous organelles (which have specific functions within the cell, such as mitochondria and chloroplasts).

Although this difference may seem subtle, it underlies a gigantic change in reproduction and other vital processes that led to a higher level of cellular complexity, without which multicellular beings with complex and superior organizations could not have been created.