Overview

Prokaryotes are small unicellular organisms that include the domains — Archaea and Bacteria. Bacteria include many common microorganisms, such as Salmonella and E. coli, while the Archaea include extremophiles that live in harsh environments, such as volcanic springs.

Like eukaryotic cells, all prokaryotic cells are surrounded by a plasma membrane, have genetic material in the form of single, circular DNA, a cytoplasm that fills the interior of the cell, and ribosomes that synthesize proteins. However, unlike eukaryotic cells, prokaryotes lack a nucleus or other membrane-bound intracellular organelles. Their cellular components float freely within the cytoplasm, although their DNA is clustered within a region called the nucleoid.

Inside the cytoplasm, many prokaryotes have small, circular, double-stranded pieces of DNA called plasmids. These are distinct from the cell's chromosomal DNA and carry just a few special genes that provide bacteria with survival advantages, such as antibiotic resistance. Plasmids are self-replicating and can be transmitted between prokaryotic cells.

Most bacteria have a cell wall made of peptidoglycan that lies outside of their plasma membrane. It physically protects the cell and helps it maintain osmotic pressure in different environments. Many bacteria also have a sticky capsule layer that covers their cell wall and allows them to stick to a substrate or each other, thus providing additional protection.

While bacteria do not have membrane-bound organelles, some have infoldings of the plasma membrane that carry out specialized functions—such as photosynthesis in cyanobacteria. Therefore, although prokaryotes are simple cells compared to eukaryotes, they do have some unique structures that help them carry out complex functions and allow them to live in a wide variety of environments.

Procedure

Prokaryotes include archaea and bacteria, simple unicellular organisms that lack membrane bound organelles.

These organisms are surrounded by a selectively permeable plasma membrane that encloses cellular components, freely suspended in the viscous cytoplasm.

Besides the plasma membrane, bacterial cells have an extra level of protection in the form of a cell wall that helps maintain their overall shape and internal osmotic pressure.

The cell wall is made up of peptidoglycan – a polymer of amino acids and sugars.

Some bacteria have another layer of defense called the capsule – a polysaccharide layer that promotes cell adhesion to surfaces.

Inside the cell, a single, double-stranded DNA is clustered in a central region called the nucleoid, where it can interact with freely floating proteins.

Most bacteria also have freely floating circular pieces of DNA, called plasmids, that can replicate independently and confer survival advantages like antibiotic resistance.

Some bacterial species may contain specific protein and lipid-bound organelles with distinct functions.

For instance, cyanobacteria possess carboxysomes and thylakoids for harvesting light energy to carry out photosynthesis.