Prokaryotic Cell Structure – OCR A Level Biology Revision Notes

Free Prokaryotic Cell Structure revision notes for OCR A Level Biology – covering specification point 2.1.1(k).

Prokaryotic organisms are defined by their lack of membrane-bound organelles, such as a nucleus.

Their DNA, typically in the form of a single circular chromosome, is free-floating in the cytoplasm in a region called the nucleoid.

The table below outlines the cell structures that can be found in prokaryotic cells:

Cell Structure	Structure	Function
Cell Wall	Made of peptidoglycan in bacteria, it varies in Archaea.	Provides mechanical support and protection. Prevents lysis when the cell is turgid.
Cytoplasm	Gel-like substance with dissolved solutes.	Site of metabolic reactions.
Ribosomes (70S)	Made of RNA.	Synthesises proteins from mRNA.
Nucleoid	Region of the cytoplasm with a circular chromosome (naked, no histones).	Contains genes. Controls cell activity via mRNA for protein synthesis.
Plasmids	Small circular DNA loops in the cytoplasm.	Carry extra genes that can be shared via conjugation.
Flagella	Long whip-like structure.	Moves the cell. Enables chemotaxis.
Pili	Short, needle-like protein projections.	Attach to surfaces or other cells. Share plasmids by conjugation.
Capsule	A thick waxy layer outside the cell wall.	Prevents drying out.

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