Question

What are characteristics of prokaryotic cells?

Answer 1

Hint: The word prokaryotic is derived from a Greek word pro- meaning primitive and karyon-meaning nucleus. Thus, prokaryotic cells are the primitive cells among all which are characterized by having no nucleus and no membrane bound organelles.

Complete answer:
The prokaryotes are the organisms having nucleus which was most primitive and are considered to be the first living organisms of earth as they are the simplest forms of life. Some basic characteristics of prokaryotic cells are:
Size: These are very small in size and cannot be seen with naked eye. Their size ranges from 0.1 to 0.5 micrometers in diameter.
Shapes: They have various shapes such as spherical (cocci), comma shaped (vibrio), rod shaped (bacillus), spiral shaped (spirillum), etc. However, the organisms with modifications of these shapes are also found in nature.
Cellular organization: The prokaryotes are primitive organisms which lack membrane bound nucleus and membrane bound organelles.
Nucleus: A well-defined nucleus is not present and it lacks a nuclear membrane which is by the way present in eukaryotic cells. It also lacks nucleolus and mitotic apparatus.
Cell wall: The cell wall of prokaryotes is made up of glycolipid layer that is made of carbohydrates and lipids and often referred to as peptidoglycan.
Reproduction: The prokaryotes are asexual that means they reproduce through asexual reproduction. No formation of gametes occurs, rather the pilli are responsible for sexual reproduction.
They do not possess complex structures like eukaryotes. Their body is composed of following parts:
Capsule: it is a polysaccharide layer that is present on the surface of some of the prokaryotes which provides them protection against other organisms.
Cell wall provides the shape and rigidity to the cell and as mentioned earlier is composed of peptidoglycan.
The cell membrane present beneath the cell wall is made up of phospholipid bilayer and provides transportation of various molecules from in and out of the cell.
The cytoplasm of the cell contains a gel-like water based cytosol containing various essential proteins and other molecules.
Ribosomes are present in cytosol which aids the translation of proteins. These are of 70s type and made up of two subunits of 30s and 50s type.
The nucleoid region contains the single circular DNA and some small pieces of extrachromosomal DNA popularly called as plasmids. Also, no mitotic apparatus is present.
The prokaryotes possess appendages such as flagella, pili and fimbriae.

Note: The plasmids that are present in the prokaryotic cells have the capability of self-replication. They carry non-essential genes and can be independently copied outside the chromosomes. Due to their self-replicating capacity, these are used as vectors in the genetic engineering technique.