Which statement about DNA structure is true?

• A. The two strands are held together by covalent bonds between complementary bases
• B. The backbone is composed of amino acids
• C. The two strands are held together by hydrogen bonds between complementary base pairs
• D. DNA consists of three separate strands

Answer: (C)

A key feature of DNA structure is that the two strands form a double helix because bases on opposite strands pair specifically: A with T and G with C. These pairs are held together by hydrogen bonds, which are weaker than covalent bonds and allow the strands to separate during replication and transcription. The backbone of each strand is a sugar-phosphate chain linked by covalent bonds, not amino acids, and the two strands run in opposite directions (antiparallel). DNA is not made of three strands. So the statement that the two strands are held together by hydrogen bonds between complementary base pairs is the correct description.