Prokaryotic Cells (Edexcel International A Level Biology): Revision Note

Cell Components: Structures

• 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

  • Ribosomes that are smaller (70 S) than those found in eukaryotic cells (80 S)

  • No nucleus, instead having a single circular bacterial chromosome that is free in the cytoplasm and is not associated with proteins

  • A cell wall that contains the glycoprotein murein 

    • Murein is sometimes known as peptidoglycan

• In addition, many prokaryotic cells also have the following structures

  • Loops of DNA known as plasmids

  • Capsules

  • Flagella (singular flagellum)

  • Pili (singular pilus)

  • A cell membrane that contains folds known as mesosomes

Bacteria are prokaryotic cells

Prokaryotes vs eukaryotes

• There are a number of important structural and physiological differences between prokaryotic and eukaryotic cells

• These differences affect their metabolic processes and how they reproduce

Comparison of Prokaryotic and Eukaryotic Cells Table

Cell Components: Functions

• The ultrastructure of prokaryotic cells includes several features that are not found in eukaryotic cells, e.g.

  • Plasmids

  • Capsule

  • Flagella

  • Pili

  • Mesosomes

  • Circular DNA

  • Ribosomes

• Some of these features are found in all prokaryotes, while some are only present in some

Additional Prokaryotic Structures Table