Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A): In a zinc finger about 30 amino acids form an elongated loop held together at the base by a single \(\text{Zn}^{2+}\) ion which is coordinated to form residues (with Cys and/or His).

Reason (R): The Zn does not itself interact with DNA, rather the coordination of Zn with amino acid residues stabilizes the small structural motif.

In the light of the above statements, choose the most appropriate answer from the options given below:

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Zn2+ coordination by Cys/His stabilises the loop, so R explains A.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:

• Assertion (A) describes the structure of a zinc finger; Reason (R) states the role of zinc. We must judge both and their relationship.

Step 2: Detailed Explanation:

• A zinc finger is a small DNA-binding motif in which about 30 amino acids fold into an elongated loop held at the base by a single Zn2+ ion coordinated by Cys and/or His residues, so (A) is correct.

• The zinc ion does not contact DNA itself; its coordination with the amino acid residues stabilises the small structural motif, so (R) is correct.

• Because the Zn2+ coordination is what holds the loop together and maintains the finger shape, (R) correctly explains how the loop in (A) is held together.

Step 3: Final Answer:
The correct option is (A) Both (A) and (R) are correct and (R) is the correct explanation of (A).