Question 7

A and T demonstrate complementary base pairing in DNA.

Complementary base pairing in DNA occurs when adenine (A) pairs with thymine (T). This specific pairing is crucial for the stable structure of the DNA double helix.

A) A and G

This option is incorrect because adenine (A) does not pair with guanine (G) in DNA. Instead, A pairs with thymine (T), while guanine pairs with cytosine (C), reflecting the specific nature of nucleotide interactions.

B) A and C

This option is also incorrect. Adenine (A) does not pair with cytosine (C). In the DNA structure, A is specifically paired with T, while C pairs with G, maintaining the integrity of the genetic code.

C) A and A

This option is incorrect as well. Adenine (A) does not pair with another adenine (A) in the DNA helix. The complementary base pairing rules dictate that A must pair with thymine (T), making this pairing invalid.

D) A and T

This option is correct because adenine (A) pairs with thymine (T) through hydrogen bonds. This complementary pairing is a fundamental aspect of DNA structure, contributing to the stability and replication of genetic material.

Conclusion

The correct answer, A and T, exemplifies the principle of complementary base pairing essential for DNA's double helix structure. All other options fail to adhere to the specific pairing rules established in molecular biology, reinforcing the importance of A pairing only with T and not with any other bases.