Question

How many hydrogen bonds link guanine and cytosine in the DNA double helix?

Options

• 1 hydrogen bond

• 4 hydrogen bonds

• 2 hydrogen bonds

• 3 hydrogen bonds

Answer 1

Guanine (G) pairs with cytosine (C) through 3 hydrogen bonds. This is one more hydrogen bond than the A-T pairing (which has 2 hydrogen bonds). The greater number of hydrogen bonds between G and C makes these regions of DNA slightly more stable, which has implications for DNA melting temperature and stability.