Question

Assertion (A) : The two strands of DNA are complementary to each other.
Reason (R) : The hydrogen bonds are formed between specific pairs of bases.

Hint:

Remember the Chargaff's rule: In a DNA molecule, the amount of Adenine equals Thymine and the amount of Guanine equals Cytosine.

Answer 1

Step 1: Understanding the Concept:
The double-helical structure of DNA is held together by specific interactions between nitrogenous bases on opposing strands.
Step 2: Detailed Explanation:
1. Assertion Analysis: DNA consists of two polynucleotide chains. These chains are not identical but are 'complementary' because the sequence of bases in one strand determines the sequence in the other. (True)
2. Reason Analysis: This complementarity arises because Adenine (A) always pairs with Thymine (T) via two hydrogen bonds, and Guanine (G) always pairs with Cytosine (C) via three hydrogen bonds. (True)
3. Relationship: Because base pairing is specific (A-T, G-C), one strand serves as a template for the other, making them complementary. Thus, R is the correct explanation for A.
Step 3: Final Answer:
Both A and R are true, and R explains A.