What are the base pairing rules for DNA?

What are the base pairing rules for DNA?

• A. A pairs with U, C pairs with G
• B. A pairs with T, C pairs with G
• C. A pairs with C, T pairs with G
• D. A pairs with T, G pairs with C

Answer: (B)

DNA base pairing keeps the double helix uniform and allows faithful copying. Adenine pairs with thymine and cytosine pairs with guanine. A-T pairing forms two hydrogen bonds, while C-G pairing forms three, which helps stabilize the DNA and preserves a consistent width because purines (A and G) pair with pyrimidines (T and C). In DNA, thymine is used (not uracil, which is found in RNA). Other pairings would create mismatches or distort the helix, so they don’t occur in standard DNA.

DNA base pairing keeps the double helix uniform and allows faithful copying. Adenine pairs with thymine and cytosine pairs with guanine. A-T pairing forms two hydrogen bonds, while C-G pairing forms three, which helps stabilize the DNA and preserves a consistent width because purines (A and G) pair with pyrimidines (T and C). In DNA, thymine is used (not uracil, which is found in RNA). Other pairings would create mismatches or distort the helix, so they don’t occur in standard DNA.