Which base pairs with Adenine?

Which base pairs with Adenine?

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

Answer: (D)

Base pairing in DNA is governed by hydrogen bonding and shape fit, so each base has a specific partner. Adenine pairs with thymine, forming two hydrogen bonds that hold the two strands together while preserving a uniform helix width. This A–T pairing happens because adenine is a purine and thymine is a pyrimidine, which lets them pair cleanly without distorting the DNA ladder. Cytosine pairs with guanine instead, via three hydrogen bonds, which is why they don’t pair with adenine. (As a note, in RNA, adenine pairs with uracil instead of thymine.)

Base pairing in DNA is governed by hydrogen bonding and shape fit, so each base has a specific partner. Adenine pairs with thymine, forming two hydrogen bonds that hold the two strands together while preserving a uniform helix width. This A–T pairing happens because adenine is a purine and thymine is a pyrimidine, which lets them pair cleanly without distorting the DNA ladder. Cytosine pairs with guanine instead, via three hydrogen bonds, which is why they don’t pair with adenine. (As a note, in RNA, adenine pairs with uracil instead of thymine.)