Question

Which of the following will be the part of the pellet, when tissue cells are homogenized and centrifuged at 1000g for 10 min.?

• A. Microsomes
• B. Mitochondria
• C. Nuclei
• D. Ribosomes

Hint:

Remember the sedimentation order for differential centrifugation by size: \textbf{N}uclei>\textbf{M}itochondria>\textbf{M}icrosomes>\textbf{R}ibosomes. A low speed like 1000g will only bring down the largest component, the nuclei.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The question describes a process called differential centrifugation, a common technique used in cell biology to separate organelles and other subcellular components from a cell homogenate based on their size, shape, and density.
The principle is that larger and denser particles sediment (form a pellet at the bottom of the tube) at lower centrifugal forces, while smaller and less dense particles remain in the supernatant and require higher forces to pellet.
Step 2: Detailed Explanation:
The standard order of fractionation by increasing centrifugal force is:


Low-speed centrifugation (e.g., 600-1000g for 10 min): This force is sufficient to pellet the largest and densest components, which are the intact cells (if any remain), the cytoskeleton, and primarily the nuclei. This first pellet is often called the nuclear pellet.

Medium-speed centrifugation (e.g., 15,000g for 20 min): The supernatant from the first step is centrifuged again at a higher speed. This pellets organelles of intermediate size and density, such as mitochondria, chloroplasts (in plant cells), lysosomes, and peroxisomes.

High-speed centrifugation (e.g., 100,000g for 60 min): The supernatant from the previous step is subjected to even higher forces, which pellets smaller components like microsomes (fragments of the endoplasmic reticulum and Golgi apparatus).

Ultracentrifugation (e.g., >150,000g for several hours): The final supernatant is centrifuged at very high speeds to pellet the smallest components, such as ribosomes, large macromolecules, and viruses.

Step 3: Final Answer:
Based on this scheme, centrifugation at 1000g for 10 minutes will specifically pellet the nuclei.