Q.29 When cell components are fractionated by sedimentation, the correct order (from
lower to higher gravitational force, g) in which the components get separated is
_______.
(A) nuclei, mitochondria, microsomes, and ribosomes
(B) microsomes, mitochondria, ribosomes, and nuclei
(C) nuclei, ribosomes, mitochondria, and microsomes
(D) ribosomes, microsomes, mitochondria, and nuclei
The correct answer is (A) nuclei, mitochondria, microsomes, and ribosomes.
Differential centrifugation separates cell components by applying increasing gravitational forces (g), where larger, denser particles sediment first at lower speeds. Nuclei pellet at the lowest g force (~600-1,000 g), followed by mitochondria (~10,000-15,000 g), microsomes (~80,000-100,000 g), and ribosomes at the highest (~150,000+ g).
Option Analysis
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(A) nuclei, mitochondria, microsomes, and ribosomes: Correct sequence matches standard differential centrifugation protocol, progressing from lowest to highest g force required for sedimentation.
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(B) microsomes, mitochondria, ribosomes, and nuclei: Incorrect; microsomes and ribosomes need much higher g than nuclei or mitochondria.
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(C) nuclei, ribosomes, mitochondria, and microsomes: Wrong; ribosomes sediment after microsomes and mitochondria due to smaller size.
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(D) ribosomes, microsomes, mitochondria, and nuclei: Reversed order; smallest particles like ribosomes require highest g force.
Centrifugation Forces
| Component | Typical g Force | Sedimentation Speed |
|---|---|---|
| Nuclei | 600-1,000 g | Lowest |
| Mitochondria | 10,000-15,000 g | Medium |
| Microsomes | 80,000-100,000 g | High |
| Ribosomes | >150,000 g | Highest |
Cell fractionation sedimentation order is a key concept in cell biology for separating organelles during differential centrifugation. This technique uses progressively higher gravitational force (g) to isolate components like nuclei, mitochondria, microsomes, and ribosomes based on size and density.
The standard cell fractionation sedimentation order starts with the largest particles sedimenting at lower g, essential for studying organelle functions in molecular biology and biotechnology.
Why This Order Matters
Larger components like nuclei (~5-10 μm) sediment first at low speeds, preventing contamination in later fractions. Mitochondria (0.5-1 μm) follow, then microsomes (vesicles from ER, ~0.1 μm), and tiniest ribosomes (~25 nm) last.
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Nuclei: ~600 g, 10 min – Contains chromatin.
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Mitochondria: ~15,000 g – Powerhouse organelles.
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Microsomes: ~100,000 g – Membrane fragments.
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Ribosomes: Ultracentrifugation – Protein synthesis sites.
CSIR NET Exam Tips
For competitive exams, remember: sedimentation follows size/density inversely with required g force. Practice with protocols to differentiate options quickly.
