Overview
This lecture explains the key structural differences between prokaryotic and eukaryotic cells, focusing on prokaryotic cell components relevant for A-Level Biology.
Prokaryotic vs. Eukaryotic Cells
- Prokaryotic cells are much smaller than eukaryotic cells.
- Prokaryotic cells do not have membrane-bound organelles.
- Eukaryotic cells contain organelles like mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, and a nucleus.
- Prokaryotes have ribosomes, but these are smaller (70S) compared to eukaryotic ribosomes (80S).
- Eukaryotic mitochondria and chloroplasts have some 70S ribosomes for their own protein synthesis.
- Prokaryotes do not have a nucleus; their DNA is circular and free in the cytoplasm.
- Eukaryotic cells have a nucleus with linear chromosomes and histone proteins.
Prokaryotic Cell Structures
- The cell wall in prokaryotes is made of murine, a glycoprotein.
- Plant eukaryotic cell walls are made of cellulose; fungi have chitin in their walls.
- Some prokaryotes have plasmids, which are small loops of extra DNA carrying a few genes (often antibiotic resistance).
- Some have a capsule, a slimy protein layer outside the cell wall, protecting against desiccation and immune system detection.
- Some prokaryotes have flagella (singular: flagellum), tail-like structures that rotate to enable movement.
Key Terms & Definitions
- Prokaryotic cell — A cell lacking membrane-bound organelles and a nucleus; example: bacteria.
- Eukaryotic cell — A cell with membrane-bound organelles and a nucleus; examples: plants, animals, fungi.
- 70S ribosome — Smaller ribosome type found in prokaryotes, mitochondria, and chloroplasts.
- 80S ribosome — Larger ribosome type found in eukaryotic cells.
- Plasmid — Small loop of DNA in prokaryotes, often carrying antibiotic resistance genes.
- Capsule — Protein layer outside some prokaryotic cells for protection.
- Flagellum/Flagella — Tail-like structure(s) enabling movement in some prokaryotes.
- Murine — Glycoprotein making up prokaryotic cell walls.
Action Items / Next Steps
- Review and memorize the differences between prokaryotic and eukaryotic cells.
- Learn the functions and structures unique to prokaryotic cells for exam questions.