Structure of Prokaryotes

Structure and Function

All cells whether prokaryotic or eukaryotic have same basic cell structure. All cells have plasma membrane which envelops it and separates it from exterior being selectively permeable. Inside the cell a large volume of cytoplasm is present which contains genetic material DNA, RNA and other cellular organelles.

Structure of Prokaryotes

Prokaryotes are single celled organisms that are most primitive forms of life on earth. Prokaryotes include bacteria and archeans. Prokaryotic cells have various shapes. The four basic shapes are Cocci (spherical), Bacilli (rod shaped), Spirochaete (spiral) and vibrio (comma shaped).

Taking bacteria as an example the outer most layer is the capsule. It is a layer of polysaccharide that protects the cell against phagocytosis. It also helps bacteria to adhere to surfaces and other cells. Capsular material is used as vaccine against some organisms (e.g., H. influenzae type b and S. pneumonia). Cell wall is composed of peptidoglycan and it gives cell its structural integrity. Its primary function is to protect cell from internal pressure caused by higher concentrations of proteins and other components compared to exterior environment. Plasma membrane is a lipid bilayer surrounding the cytoplasm and regulates the flow of substances in and out of the cell.

Bacteria have appendages like flagella and pilli. Flagella are extra cellular whip like structure protruding from cell wall and responsible for locomotion. Pilli are hollow, hair like structures made of protein. Their function is to facilitate attachment to other organisms and also involve in conjugation.

In the cytoplasm, there is nucleoid which contains the genetic material. Bacteria also have extra chromosomal material called plasmid. Ribosomes are the intracellular multiprotein complexes found in bacteria. This is the site of protein synthesis in living organisms. Bacteria have 70S ribosome which is made up of 50S and 30S subunits