Which base pairing forms three hydrogen bonds?

Which base pairing forms three hydrogen bonds?

• A. G-C
• B. A-T/U
• C. A-C
• D. G-U

Answer: (A)

The amount of hydrogen bonding between paired bases influences how stable the pair is. Guanine paired with cytosine forms three hydrogen bonds, using multiple complementary sites on each base, which makes this pair more thermodynamically stable than others. Adenine pairing with thymine (in DNA) or uracil (in RNA) forms two hydrogen bonds, so it’s not the three-bond case. A–C isn’t a standard, stable Watson-Crick pair, and guanine–uracil is a wobble combination in RNA that typically involves two hydrogen bonds, not three. So the trio of hydrogen bonds is unique to guanine–cytosine.

The amount of hydrogen bonding between paired bases influences how stable the pair is. Guanine paired with cytosine forms three hydrogen bonds, using multiple complementary sites on each base, which makes this pair more thermodynamically stable than others. Adenine pairing with thymine (in DNA) or uracil (in RNA) forms two hydrogen bonds, so it’s not the three-bond case. A–C isn’t a standard, stable Watson-Crick pair, and guanine–uracil is a wobble combination in RNA that typically involves two hydrogen bonds, not three. So the trio of hydrogen bonds is unique to guanine–cytosine.