Overview
This lecture covers the key differences between prokaryotic and eukaryotic cells, focusing on their structures and defining features important for A-level biology.
Key Differences: Prokaryotic vs. Eukaryotic Cells
- Prokaryotic cells are much smaller than eukaryotic cells.
- Prokaryotic cells lack membrane-bound organelles (e.g., mitochondria, nucleus, Golgi apparatus).
- Both cell types have ribosomes, but prokaryotic ribosomes are smaller (70S vs 80S).
- Eukaryotic cells have a nucleus with a nuclear envelope, while prokaryotic cells have free, circular DNA.
- Prokaryotic cell walls contain murine, a glycoprotein; plant cell walls have cellulose, fungi have chitin.
- Prokaryotic cells may contain plasmids, capsules, and flagella, which are not always present.
Ribosomes
- Prokaryotic ribosomes (70S) are smaller than eukaryotic ribosomes (80S).
- Eukaryotic mitochondria and chloroplasts contain some 70S ribosomes for their own protein synthesis.
Genetic Material
- Eukaryotes have linear chromosomes within the nucleus, associated with histone proteins.
- Prokaryotes have circular DNA without histones, located in the cytoplasm.
Cell Wall Composition
- Plant cell walls: cellulose; fungal cell walls: chitin; prokaryotic cell walls: murine.
Additional Prokaryotic Structures
- Plasmids: small loops of DNA carrying extra genes (e.g., antibiotic resistance).
- Capsule: thick, slimy protein layer protecting against desiccation and immune response.
- Flagella (plural; flagellum, singular): rotating tail-like structures for movement.
Key Terms & Definitions
- Prokaryotic cell — Cell without a nucleus or membrane-bound organelles, e.g., bacteria.
- Eukaryotic cell — Cell with a nucleus and membrane-bound organelles.
- Ribosome — Organelle for protein synthesis; 70S in prokaryotes, 80S in eukaryotes.
- Murine — Glycoprotein making up prokaryotic cell walls.
- Plasmid — Small, circular DNA in prokaryotes, often carrying resistance genes.
- Capsule — Protective protein layer outside some prokaryotic cell walls.
- Flagellum (Flagella) — Whip-like structure used for movement in some bacteria.
Action Items / Next Steps
- Review comparison tables of cell structure differences.
- Memorize key definitions and functions of each structure.