OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

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What is the complementary base pairing for Adenine in DNA?

Guanine
Thymine
Cytosine
Uracil

The correct answer is: Thymine

In DNA, the complementary base pairing for Adenine is Thymine. This means that in the double helix structure of DNA, Adenine (A) on one strand pairs with Thymine (T) on the opposite strand through two hydrogen bonds. This specific pairing is crucial for the accuracy of DNA replication and for maintaining the genetic code. The rules of complementary base pairing ensure that the genetic information is correctly transmitted during cell division and that proteins are accurately synthesized based on the encoded instructions in the DNA. Other bases, such as Guanine, Cytosine, and Uracil, do not pair with Adenine in DNA. Guanine pairs with Cytosine, and Uracil, which is found in RNA, pairs with Adenine in RNA but not in DNA, making Thymine the correct complement for Adenine in the context of DNA.