Prokaryotic and Eukaryotic Cells — Revision Notes

⚡ 30-Second Revision

Prokaryotes: — No true nucleus, no membrane-bound organelles, 70S ribosomes, single circular DNA (nucleoid), peptidoglycan cell wall (bacteria), binary fission. E.g., Bacteria, Archaea.
Eukaryotes: — True nucleus, membrane-bound organelles (ER, Golgi, mitochondria, etc.), 80S ribosomes (cytoplasmic), multiple linear DNA (chromosomes with histones), cellulose/chitin cell wall or absent, mitosis/meiosis. E.g., Plants, Animals, Fungi, Protists.
Common: — Cell membrane, cytoplasm, ribosomes, genetic material.
Endosymbiotic Theory: — Mitochondria & chloroplasts have 70S ribosomes & circular DNA, supporting prokaryotic origin.

2-Minute Revision

Prokaryotic and eukaryotic cells represent the two fundamental blueprints of life. Prokaryotes, like bacteria, are simpler, lacking a membrane-bound nucleus and other membrane-bound organelles. Their genetic material is a single, circular chromosome in the nucleoid, and they possess 70S ribosomes.

They divide by binary fission. Eukaryotes, encompassing plants, animals, fungi, and protists, are more complex. They feature a true, membrane-bound nucleus housing multiple linear chromosomes associated with histones.

They are rich in membrane-bound organelles like the endoplasmic reticulum, Golgi apparatus, mitochondria, and lysosomes, which facilitate compartmentalization and specialized functions. Eukaryotic cells have 80S ribosomes in their cytoplasm and divide via mitosis or meiosis.

Both cell types share a cell membrane, cytoplasm, and ribosomes, highlighting their common ancestry while emphasizing their evolutionary divergence.

5-Minute Revision

A comprehensive understanding of prokaryotic and eukaryotic cells is crucial for NEET. Start by firmly grasping the core distinction: the presence or absence of a true, membrane-bound nucleus. Prokaryotes (bacteria, archaea) lack this, housing their single, circular DNA in a nucleoid.

They also lack all other membrane-bound organelles, relying on their cytoplasm and cell membrane for metabolic functions. Their ribosomes are 70S. Many have a peptidoglycan cell wall and may possess plasmids for extra genetic information, flagella for motility, and pili for attachment/conjugation.

They reproduce by binary fission.

Eukaryotes (plants, animals, fungi, protists) are far more complex. Their genetic material, organized into multiple linear chromosomes with histones, is enclosed within a double-membraned nucleus. They exhibit extensive compartmentalization with a variety of membrane-bound organelles: the Endoplasmic Reticulum (RER for protein synthesis, SER for lipid synthesis/detoxification), Golgi apparatus (modification, packaging, transport), lysosomes (digestion), and vacuoles (storage, turgor).

Mitochondria (cellular respiration) and chloroplasts (photosynthesis in plants/algae) are unique semi-autonomous organelles, possessing their own 70S ribosomes and circular DNA, supporting the endosymbiotic theory.

Cytoplasmic ribosomes are 80S. Eukaryotic cells divide by mitosis (somatic) or meiosis (germ cells). Plant cells uniquely have a cellulose cell wall and a large central vacuole, while animal cells lack a cell wall and chloroplasts.

Fungi have chitin cell walls but no chloroplasts. Focus on these specific structural and functional differences, as well as the commonalities like the cell membrane and ribosomes, to tackle comparative questions effectively.

Prelims Revision Notes

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Prokaryotic Cells (Bacteria, Archaea):

* Nucleus: Absent. Genetic material (DNA) is in a non-membrane-bound region called the nucleoid. * Genetic Material: Typically a single, circular chromosome. May also have plasmids (extra-chromosomal circular DNA).

* Membrane-bound Organelles: Absent (e.g., no mitochondria, ER, Golgi, lysosomes). * Ribosomes: 70S type (composed of 50S and 30S subunits), free in cytoplasm. * Cell Wall: Present in most bacteria, made of peptidoglycan (murein).

* Cell Membrane: Present, involved in respiration and transport. * Cytoplasm: Lacks cytoplasmic streaming. * Inclusions: Non-membrane-bound storage granules (e.g., phosphate, glycogen).

* Motility: May have flagella (filament, hook, basal body) for movement. * Attachment: Pili and fimbriae for attachment and conjugation. * Cell Division: Binary fission.

* Size: Generally smaller (0.1-5 $\mu$m).

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Eukaryotic Cells (Plants, Animals, Fungi, Protists):

* Nucleus: Present, true membrane-bound nucleus containing genetic material. * Genetic Material: Multiple, linear chromosomes, associated with histone proteins (forming chromatin). * Membrane-bound Organelles: Present and highly specialized: * Endoplasmic Reticulum (ER): RER (ribosomes, protein synthesis) and SER (lipid synthesis, detoxification).

* Golgi Apparatus: Modifies, sorts, packages proteins/lipids. * Lysosomes: Contain hydrolytic enzymes for digestion. * Vacuoles: Storage, waste, turgor (large central in plants). * Mitochondria: 'Powerhouse', aerobic respiration, 70S ribosomes, circular DNA (evidence for endosymbiotic theory).

* Chloroplasts (Plants/Algae): Photosynthesis, 70S ribosomes, circular DNA (evidence for endosymbiotic theory). * Ribosomes: 80S type (composed of 60S and 40S subunits), free or attached to RER.

* Cell Wall: Present in plants (cellulose) and fungi (chitin); absent in animals. * Cell Membrane: Present, fluid mosaic model. * Cytoplasm: Cytoplasmic streaming common. * Cytoskeleton: Microfilaments, microtubules, intermediate filaments for support and movement.

* Motility/Movement: Cilia and flagella (9+2 arrangement) in some cells. * Cell Division: Mitosis (somatic cells) and Meiosis (germ cells). * Size: Generally larger (10-100 $\mu$m).

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Common Features (Both Prokaryotic & Eukaryotic):

* Cell membrane (plasma membrane) * Cytoplasm * Ribosomes (though different types) * Genetic material (DNA)

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Key Distinctions for NEET: — Nucleus, membrane-bound organelles, ribosome type, cell wall composition, genetic material organization, cell division method.

Vyyuha Quick Recall

To remember the key differences, think of 'N.O.R.M.S. C.D.':

Nucleus: Pro-NO, Eu-YES
Organelles (membrane-bound): Pro-NO, Eu-YES
Ribosomes: Pro-70S, Eu-80S
Material (Genetic): Pro-Circular, Eu-Linear
Size: Pro-Small, Eu-Large
Cell Wall: Pro-Peptidoglycan, Eu-Cellulose/Chitin (or absent)
Division: Pro-Binary Fission, Eu-Mitosis/Meiosis