Question
What are the differences between prokaryotic and eukaryotic cells? Give a comparison table with at least 8 distinguishing features.
Solution — Step by Step
Prokaryote comes from Greek: pro = before, karyon = nucleus. Prokaryotes existed before cells developed a proper nucleus.
Eukaryote: eu = true, karyon = nucleus. Eukaryotes have a true, membrane-bound nucleus.
This fundamental difference — presence or absence of a nuclear membrane — is the defining criterion.
The nucleus difference leads to a cascade of structural differences:
- Prokaryotes lack membrane-bound organelles entirely
- Their DNA is circular, not linear
- They have no cytoskeleton
- Cell division is simpler (binary fission, not mitosis/meiosis)
| Feature | Prokaryotic Cell | Eukaryotic Cell |
|---|---|---|
| Nuclear membrane | Absent | Present |
| True nucleus | Absent (nucleoid region) | Present |
| Size | Smaller (1–10 µm) | Larger (10–100 µm) |
| DNA structure | Circular, no histone proteins | Linear, with histone proteins |
| Membrane-bound organelles | Absent | Present (mitochondria, ER, Golgi) |
| Ribosomes | 70S (50S + 30S subunits) | 80S (60S + 40S subunits) |
| Cell wall | Present (peptidoglycan in bacteria) | Present in plants (cellulose), absent in animals |
| Cytoskeleton | Absent | Present |
| Cell division | Binary fission | Mitosis and meiosis |
| Reproduction | Asexual only | Sexual and asexual |
| Plasmids | Common | Rare (except yeast) |
| Examples | Bacteria, Archaea | Fungi, Protists, Plants, Animals |
The ribosome difference (70S vs 80S) is biologically significant. Many antibiotics (like streptomycin, chloramphenicol) specifically target 70S ribosomes, killing bacteria without harming human cells (which have 80S ribosomes). This is the molecular basis of antibiotic selectivity.
Why This Works
The fundamental separation between prokaryotes and eukaryotes represents one of the deepest evolutionary divides in life. All multicellular organisms (animals, plants, fungi) are eukaryotes. Unicellular bacteria and archaea are prokaryotes.
The compartmentalisation in eukaryotes — having separate membrane-bound compartments for different functions — allowed for greater metabolic complexity and eventually for multicellular life.
Alternative Method — Remember by Exception
Instead of memorising what prokaryotes lack, remember: prokaryotes are the “stripped down” version. They have: DNA, ribosomes, cell membrane, cytoplasm. That’s roughly it. Everything else (membrane-bound organelles, nuclear envelope, cytoskeleton, linear chromosomes) is eukaryotic.
Common Mistake
Saying prokaryotes have “no ribosomes.” This is wrong — bacteria absolutely have ribosomes (70S). Ribosomes are the only organelles present in prokaryotes. The distinction is that prokaryotes lack membrane-BOUND organelles. Ribosomes are not membrane-bound, so they are present in both cell types.