Question

The linking number (L) of a supercoiled duplex DNA can be equated to its Twist (T) and Writhe (W) by which one of the following expression?

• A. L = T + W
• B. L = T/W
• C. L = T × W
• D. L = T - W

Hint:

L = T + W (White's theorem).
L is a topological invariant.
T describes helical turns, W describes supercoiling.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
This question tests knowledge of DNA supercoiling topology.

Step 2: Detailed Explanation:
The relationship between L, T, and W is: L = T + W (White's theorem).
- L (Linking number): The number of times one strand winds around the other.
- T (Twist): The number of helical turns (right-handed).
- W (Writhe): The coiling of the DNA helix axis in space.
This equation is a topological invariant.
Other expressions (B, C, D) are incorrect.

Step 3: Final Answer:
Thus, L = T + W, which corresponds to option (A).
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