During DNA replication, which base pairs form between the two strands?

During DNA replication, which base pairs form between the two strands?

• A. A with T; C with G
• B. A with C; G with T
• C. A with U; G with C
• D. G with A; C with T

Answer: (A)

Base pairing follows a fixed rule that keeps the DNA double helix uniform and enables faithful copying. In DNA, adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). This is because A–T forms two hydrogen bonds and G–C forms three, which stabilizes the two strands while preserving the consistent width of the helix. During replication, the two strands separate and each serves as a template. The new strand is built by adding nucleotides that are complementary to the template, so wherever there was A on the template, T is added on the new strand, and wherever there was G, C is added. This A–T and G–C pairing is specific to DNA; pairing A with C or G with T would disrupt the helix geometry, and pairing A with U occurs in RNA, not DNA.

Base pairing follows a fixed rule that keeps the DNA double helix uniform and enables faithful copying. In DNA, adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). This is because A–T forms two hydrogen bonds and G–C forms three, which stabilizes the two strands while preserving the consistent width of the helix.

During replication, the two strands separate and each serves as a template. The new strand is built by adding nucleotides that are complementary to the template, so wherever there was A on the template, T is added on the new strand, and wherever there was G, C is added. This A–T and G–C pairing is specific to DNA; pairing A with C or G with T would disrupt the helix geometry, and pairing A with U occurs in RNA, not DNA.