In DNA, adenine pairs with __________.

In DNA, adenine pairs with __________.

• A. Thymine
• B. Adenine
• C. Cytosine
• D. Guanine

Answer: (A)

DNA uses complementary base pairing, so each base on one strand has a specific partner on the opposite strand. Adenine pairs with thymine in DNA because they fit as a purine-pyrimidine pair and can form two hydrogen bonds, which helps keep the double helix width uniform and the genetic code readable. This pairing also aligns with Chargaff’s rules, which state that the amount of adenine equals thymine in DNA. For contrast, cytosine pairs with guanine, forming three hydrogen bonds and a different pairing pattern. In RNA, adenine pairs with uracil instead of thymine, but within DNA the partner is thymine.

DNA uses complementary base pairing, so each base on one strand has a specific partner on the opposite strand. Adenine pairs with thymine in DNA because they fit as a purine-pyrimidine pair and can form two hydrogen bonds, which helps keep the double helix width uniform and the genetic code readable. This pairing also aligns with Chargaff’s rules, which state that the amount of adenine equals thymine in DNA. For contrast, cytosine pairs with guanine, forming three hydrogen bonds and a different pairing pattern. In RNA, adenine pairs with uracil instead of thymine, but within DNA the partner is thymine.