Site author Richard Steane
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Bacterial cell structure

This unit contains some information to assist you in relation to other units, and some supplementary details - pass your mouse cursor over the green text (and click on underlined text to hear it spoken).
Bacteria consist of single cells. They are much smaller than animal or plant cells.

These cells have several similarities with cells of (green) plants and animals, but lots of differences, which is why they are put into a kingdom of their own.

On the outside of the cell is a cell wall, but it is not usually made of cellulose.

Inside this is a membrane enclosing the cytoplasm.

The genetic material is not enclosed in a nuclear membrane like higher plants and animals. The main genetic material is DNA, in a diffuse blob, loose in the cytoplasm. Also in the cytoplasm there may be other loops of DNA which are called plasmids. This plasmid DNA is likely to contain genes for other characteristics.

There are no mitochondria in bacterial cells. In fact they are about the same size as one another.

Likewise, there are no chloroplasts in bacterial cells.

Bacterial cells do contain ribosomes, but they are slightly smaller than ribosomes in animal and plant cells.

Approximate sizes:

in micrometres (µm) also known as microns
[1µm = 0.001mm = 0.000001m (10-6m)]

cell/component size / µm
E. coli cell length 2
E. coli cell width 0.5
Staphylococcus aureus cell diameter 0.6 (600nm)
bacterial ribosome 0.020 (20nm)

Going down another 1000 ×

Another unit - the nanometer - is often used to describe lengths of structures seen with the electron microscope.
[1nm = 0.001 µm = 0.000001mm = 0.000000001m (10-9m)]

What you should know

A bacterial cell consists of cytoplasm and a membrane surrounded by a cell wall;
the genes are not in a distinct nucleus;
some of the genes are located in circular structures called plasmids.

Notes on words:

Bacterium is singular, bacteria plural.

Bacterial is an adjective, meaning to do with bacteria.
Escherichia coli (E.coli)
- a "colo(u)rized scanning electron micrograph
(SEM)" from CDC Atlanta rod-shaped bacterium - a bacillus
Click (or tap) above for the internal details

Staphylococcus aureus
This means the golden Staphylococcus, but this scanning electron microscope image has been colo(u)rised blue.
several spherical bacteria - cocci

This topic has connections with other units on this site:
Cell biology
Eukaryotes and prokaryotes
Animal cells
Plant cells
Yeast cells

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