A Level Biology Practice Exam

Which base pairs with adenine during complementary base pairing?

1. Guanine

2. Thymine or Uracil

3. Cytosine

4. None of the above

The correct answer is: Thymine or Uracil

The correct response indicates that thymine pairs with adenine in DNA, while uracil performs a similar role in RNA. During complementary base pairing, adenine forms hydrogen bonds specifically with thymine when DNA is involved, and with uracil when dealing with RNA. This specificity is crucial for the accurate replication and transcription processes in nucleic acids, ensuring that genetic information is reliably passed on and expressed. Guanine and cytosine, while important, pair together instead. The mention of "none of the above" is not applicable, as thymine and uracil are indeed paired with adenine in their respective nucleic acids. Thus, the pairing between adenine and either thymine or uracil is fundamental to the structure and function of DNA and RNA, respectively.