Humber Admissions Practice Test

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What is the only base that pairs with adenine in DNA?

Uracil
Guanine
Cytosine
Thymine

The correct answer is: Thymine

In the structure of DNA, adenine is a purine that specifically pairs with thymine, a pyrimidine, through hydrogen bonds. This pairing is crucial for the formation of the double helix structure of DNA, allowing for the complementary base pairing that ensures accurate DNA replication and transcription processes. The pairing between adenine and thymine involves two hydrogen bonds, which helps stabilize the DNA molecule. This complimentary pairing is fundamental to the overall structure and function of DNA, as it supports the genetic code and the mechanisms involved in cell division and protein synthesis. Other bases, such as uracil, guanine, and cytosine, do not pair with adenine in DNA. In fact, uracil replaces thymine in RNA, and while guanine pairs with cytosine in both DNA and RNA, they do not form pairs with adenine. Therefore, the only base that specifically pairs with adenine in DNA is thymine.