Prokaryotic Cells

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.