Prokaryote kingdom

Prokaryotes are single-celled organisms. Each organism consists of one cell, whose genetic material is not enclosed in a nucleus.

A prokaryotic cell contains cytoplasm surrounded by a cell membrane. Most prokaryotic cells also have a cell wall outside the membrane. Their genetic material is found within the cell but is not separated from the cytoplasm by a nucleus.

This absence of a nucleus distinguishes prokaryotic cell organisation from that of animals, plants, fungi and protoctists, whose cells have nuclei enclosing their genetic material.

Bacterial cell structure

A bacterial cell has an outer cell wall surrounding a cell membrane. Inside the membrane are the cytoplasm, ribosomes and genetic material. Unlike a cell with a nucleus, a bacterial cell has its main DNA in the cytoplasm, not enclosed inside a nucleus.

Bacterial cell structures and their functions

• Cell wall: supports and protects the cell. In a diagram, it forms the outer layer around the cell membrane.
• Cell membrane: controls the movement of substances into and out of the cell. It lies just inside the cell wall.
• Cytoplasm: the material filling the inside of the cell, where many chemical reactions occur.
• Ribosomes: small structures in the cytoplasm that make proteins. They are often shown as dots in diagrams.

Bacterial DNA and plasmids

The bacterium’s main genetic material is circular DNA in the cytoplasm. In a diagram, it is often drawn as a large loop, which may appear tangled or folded.

Some bacterial cells also contain plasmids: smaller circles of DNA separate from the main circular DNA. In a diagram, these can be recognised as small loops in the cytoplasm. Plasmids are not present in every bacterial cell.