Structural Differences — Revision Notes

⚡ 30-Second Revision

Prokaryotes: — No true nucleus, DNA in nucleoid. No membrane-bound organelles. 70S ribosomes. Cell wall: peptidoglycan (bacteria). Binary fission. Small size ($0.1-5,mu\text{m}$). No histones.
Eukaryotes: — True nucleus, DNA in chromosomes with histones. Membrane-bound organelles (mitochondria, ER, Golgi, etc.). 80S ribosomes (cytoplasmic). Cell wall: cellulose (plants), chitin (fungi), absent (animals). Mitosis/Meiosis. Large size ($10-100,mu\text{m}$).

2-Minute Revision

The core distinction between prokaryotic and eukaryotic cells revolves around internal compartmentalization. Prokaryotes (bacteria, archaea) are simpler, lacking a membrane-bound nucleus and all other membrane-bound organelles.

Their genetic material is a single circular chromosome in the nucleoid, and they possess 70S ribosomes. Cell division occurs via binary fission, and bacterial cell walls are made of peptidoglycan. Eukaryotes (animals, plants, fungi, protists) are complex, featuring a true nucleus enclosing linear chromosomes associated with histones.

They are rich in specialized membrane-bound organelles like mitochondria, ER, and Golgi, and have 80S ribosomes in the cytoplasm. Cell walls, if present, are cellulose or chitin, and cell division is by mitosis or meiosis.

This fundamental difference in organization dictates their functional capabilities and evolutionary paths.

5-Minute Revision

To quickly revise the structural differences, visualize a simple bacterial cell versus a complex animal or plant cell. The most striking difference is the nucleus: prokaryotes lack a true, membrane-bound nucleus, housing their single circular DNA in a region called the nucleoid, without histone proteins.

Eukaryotes, conversely, have a well-defined nucleus with a nuclear envelope, containing multiple linear chromosomes tightly wound around histone proteins. This nuclear organization impacts gene regulation and cell division.

Next, consider organelles: prokaryotes are devoid of all membrane-bound organelles. Their metabolic functions occur in the cytoplasm or on the plasma membrane. Eukaryotes are packed with specialized membrane-bound organelles like mitochondria (ATP production), endoplasmic reticulum (protein/lipid synthesis), Golgi apparatus (packaging/modification), and lysosomes (waste breakdown). Plant cells add chloroplasts (photosynthesis) and a large central vacuole.

Ribosomes are present in both but differ: 70S in prokaryotes, 80S in eukaryotic cytoplasm (with 70S in mitochondria/chloroplasts). The cell wall is another key differentiator: peptidoglycan in bacteria, cellulose in plants, chitin in fungi, and absent in animals.

Finally, remember cell division: binary fission for prokaryotes, and the more complex mitosis/meiosis for eukaryotes. These distinctions are not just academic; they explain why antibiotics target bacterial cells specifically or how eukaryotic cells achieve greater functional specialization.

Prelims Revision Notes

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Nucleus:

* Prokaryotes: Absent (no true nucleus). Genetic material in nucleoid region. * Eukaryotes: Present (true, membrane-bound nucleus).

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Genetic Material:

* Prokaryotes: Single, circular chromosome. Not associated with histones. Plasmids common. * Eukaryotes: Multiple, linear chromosomes. Associated with histones (forming chromatin).

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Membrane-bound Organelles:

* Prokaryotes: Absent (no mitochondria, ER, Golgi, lysosomes, chloroplasts, etc.). * Eukaryotes: Present (all mentioned above).

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Ribosomes:

* Prokaryotes: 70S type (50S + 30S subunits). * Eukaryotes: 80S type (60S + 40S subunits) in cytoplasm; 70S in mitochondria/chloroplasts.

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Cell Wall:

* Prokaryotes (Bacteria): Composed of peptidoglycan (murein). * Prokaryotes (Archaea): Pseudopeptidoglycan or other layers. * Eukaryotes (Plants): Composed of cellulose. * Eukaryotes (Fungi): Composed of chitin. * Eukaryotes (Animals): Absent.

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Plasma Membrane:

* Prokaryotes: Lacks sterols (except Mycoplasma). * Eukaryotes: Contains sterols (e.g., cholesterol).

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Cytoskeleton:

* Prokaryotes: Rudimentary or absent (homologs like FtsZ, MreB). * Eukaryotes: Well-developed (microtubules, microfilaments, intermediate filaments).

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Cell Size:

* Prokaryotes: Smaller ($0.1 - 5.0,mu\text{m}$). * Eukaryotes: Larger ($10 - 100,mu\text{m}$).

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Cell Division:

* Prokaryotes: Binary fission. * Eukaryotes: Mitosis (somatic cells), Meiosis (germ cells).

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Locomotion:

* Prokaryotes: Simple flagella (rotary), pili. * Eukaryotes: Complex flagella/cilia (whip-like), pseudopods.

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Examples:

* Prokaryotes: Bacteria, Archaea. * Eukaryotes: Animals, Plants, Fungi, Protists.

Vyyuha Quick Recall

Pro-Karyotes are Primitive, Kompartment-less, Peptidoglycan-walled, 70S ribosomes, Binary fission. Eu-Karyotes are Evolved, Kompartmentalized, Cellulose/Chitin-walled, 80S ribosomes, Mitosis/Meiosis.