Can you recall what centrifugal force is, and think why a molecule with higher mass/density would sediment faster?
Centrifugal force is the outward force experienced when a substance is rotated at high speed in a centrifuge. This force pushes particles away from the center of rotation, causing them to move outward.
Molecules with higher mass/density sediment faster because they experience a greater outward pull under centrifugal force. As demonstrated in the context, heavy DNA containing the N isotope could be distinguished from normal DNA by centrifugation in a CsCl density gradient. The heavier N-DNA sediments faster and separates from lighter molecules, forming distinct bands based on density differences. Similarly, in DNA fingerprinting, density gradient centrifugation separates repetitive DNA from bulk genomic DNA as different peaks.
Explanation
This question tests the student's understanding of how centrifugation works in molecular biology experiments. The textbook context shows the application of this principle in Meselson and Stahl's experiment, where DNA with heavy nitrogen (N) was separated from normal DNA based on density differences using CsCl density gradient centrifugation. The same principle is applied in DNA fingerprinting to separate satellite DNA. A 2-mark answer should briefly explain centrifugal force and connect it to the experimental evidence shown in the context.
Solution Steps
Step 1: Define centrifugal force as the outward force during rotation
Step 2: Explain that heavier/denser molecules experience greater force and sediment faster
Step 3: Support with example from context - separation of N-DNA from normal DNA in CsCl gradient