34. A cell suspension was subjected to membrane disruption followed by differential
centrifugation to fractionate the cellular components.
Match the centrifugal conditions in Column I to the appropriate subcellular components in
Column II.
Column I                             Column II
P. 1000 g, 10 min              i. Microsomes and small vesicles
Q. 20000 g, 30 min          ii. Ribosomes
R. 80000 g, 1 hour            iii. Nuclei
S. 150000 g, 3 hours          iv. Lysosomes and peroxisomes
(A) P-iii ; Q-iv ; R-i ; S-ii
(B) P-i ; Q-iv ; R-iii ; S-ii
(C) P-iii ; Q-iv ; R-ii ; S-i
(D) P-ii ; Q-i ; R-iv; S-iii

This article dives into a classic biochemistry question on differential centrifugation for isolating subcellular components. It explains the correct matching of centrifugal conditions to organelles, why it works that way, and breaks down all multiple-choice options. Perfect for students prepping for exams in molecular biology or cell biology.

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What Is Differential Centrifugation?

Differential centrifugation separates cellular components based on size and density. After disrupting cell membranes (e.g., homogenization), you spin the suspension at increasing speeds and times. Larger, denser particles sediment first at lower forces, while smaller ones need higher g-forces and longer spins.

This technique fractions organelles like nuclei, mitochondria, and ribosomes. Sedimentation follows Stokes’ law: velocity depends on particle radius squared, density difference, and centrifugal force.

The Question Breakdown

A cell suspension undergoes membrane disruption, then differential centrifugation. Match these from Column I (centrifugal conditions) to Column II (subcellular components):

Column I
P. 1000 g, 10 min
Q. 20,000 g, 30 min
R. 80,000 g, 1 hour
S. 150,000 g, 3 hours

Column II
i. Microsomes and small vesicles
ii. Ribosomes
iii. Nuclei
iv. Lysosomes and peroxisomes

Options:
(A) P-iii ; Q-iv ; R-i ; S-ii
(B) P-i ; Q-iv ; R-iii ; S-ii
(C) P-iii ; Q-iv ; R-ii ; S-i
(D) P-ii ; Q-i ; R-iv ; S-iii

Correct Answer: (A) P-iii ; Q-iv ; R-i ; S-ii

Here’s why A is right, tied to standard protocols (e.g., from Alberts’ Molecular Biology of the Cell or lab manuals):

• P. 1000 g, 10 min → iii. Nuclei: Low speed pellets large nuclei (5-10 μm diameter). They’re the heaviest, sedimenting quickly without dragging down lighter bits.

• Q. 20,000 g, 30 min → iv. Lysosomes and peroxisomes: Medium force catches these (0.5-1 μm). Mitochondria often pellet here too in some protocols, but lysosomes/peroxisomes fit this range post-nuclear spin.

• R. 80,000 g, 1 hour → i. Microsomes and small vesicles: High speed sediments endoplasmic reticulum fragments (microsomes, ~0.1 μm) and vesicles from Golgi/plasma membrane.

• S. 150,000 g, 3 hours → ii. Ribosomes: Ultrahigh speed for tiny ribosomes (20-30 nm). Needs extreme force/time; supernatant after this is cytosol.

This sequence isolates fractions from crude lysate: nuclear (P), lysosomal/peroxisomal (Q), microsomal (R), ribosomal (S).

Why Other Options Are Wrong

Let’s evaluate each incorrect choice step-by-step:

Option (B) P-i ; Q-iv ; R-iii ; S-ii

• Wrong at P and R. Nuclei (iii) don’t stay in supernatant till 1000 g (they pellet), and microsomes (i) won’t sediment at low speed—too small. R assigns nuclei to 80,000 g, but they’d already pellet earlier.

Option (C) P-iii ; Q-iv ; R-ii ; S-i

• Correct for P and Q, but swaps R and S. Ribosomes (ii) need >100,000 g, not 80,000 g (that’s microsomes). Microsomes (i) pellet faster than ribosomes.

Option (D) P-ii ; Q-i ; R-iv ; S-iii

• Completely off. Nuclei (iii) aren’t last at 150,000 g (S assigns them there). Ribosomes (ii) don’t pellet at 1000 g (P). Lysosomes/peroxisomes (iv) sediment mid-range, not high.

Quick Reference Table: Standard Centrifugation Forces

Exam Tips for Cell Fractionation Questions

• Remember the order: low g/time = big/heavy (nuclei → mitochondria/lysosomes → microsomes → ribosomes).

• Protocols vary slightly (e.g., sucrose gradients refine), but basics hold.

• Visualize: Bigger particles fall faster, like rocks vs. sand in a spin dryer.