Structure of Prokaryotic Cells (AQA A Level Biology): Revision Note

Prokaryotic cells

• Animal and plant cells are types of eukaryotic cells, whereas bacteria are a type of prokaryote

• Prokaryotic cells are much smaller than eukaryotic cells

• They also differ from eukaryotic cells in having:

  • A cytoplasm that lacks membrane-bound organelles

  • Smaller, 70S ribosomes (in comparison to 80S ribosomes found in eukaryotic cells )

  • No nucleus (instead, they have a single circular DNA molecule that is free in the cytoplasm and is not associated with proteins)

  • A cell wall that contains murein (a glycoprotein)

Additional structures in prokaryotic cells

• Some prokaryotic cells also have:

  • Plasmids:

    • Small, circular loops of DNA

    • Carry non-essential genes (e.g. antibiotic resistance)

    • Can be transferred between prokaryotes

  • Capsule (slime capsule):

    • Protective outer layer

    • Prevents desiccation and helps evade immune system attack

  • Flagella (singular: flagellum):

    • Long, rotating tail for motility

    • Some bacteria have multiple flagella