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Bacterial cells

Key concepts in biology · Cell structure and specialised cells · note 2 of 3

Spec 1.1Download these notes (PDF)5 pages

Bacterial cellsSpec 1.1

Bacteria are prokaryotic cells. They do not have a nucleus. Their genetic material is found free in the cytoplasm.

Chromosomal DNA
A single loop of DNA found free in the cytoplasm, not enclosed in a nucleus.
Plasmid DNA
Small rings of extra DNA, separate from the chromosomal DNA.
Cell membrane
Controls the movement of substances into and out of the cell.
Ribosomes
Where proteins are made.
Flagellum
A long, whip-like structure that moves to make the bacterium swim. Some bacteria have one or more flagella.
Eukaryotic and prokaryotic cells compared
FeatureEukaryotic cell (animal, plant)Prokaryotic cell (bacterium)
NucleusPresent, contains the DNAAbsent
Where the DNA isInside the nucleusFree in the cytoplasm
PlasmidsNot presentOften present
MitochondriaPresentAbsent
FlagellaNot presentPresent in some
Labelled diagram of a bacterial cell showing chromosomal DNA as a single loop free in the cytoplasm, small rings of plasmid DNA, ribosomes, the cell membrane and a flagellum.Tap to enlarge
A bacterial cell: the DNA is not in a nucleus. It is a single loop, plus small rings called plasmids.