The two strands of a DNA double helix are described as antiparallel, which means that
- A. they carry identical base sequences
- B. one runs 5' to 3' while the other runs 3' to 5'
- C. they are held together by covalent bonds
- D. they coil in opposite directions around each other
Explanation
Antiparallel refers to the direction of the sugar-phosphate backbones: one strand runs 5' to 3' while its partner runs 3' to 5'. This is why replication is continuous on the leading strand and discontinuous, in Okazaki fragments, on the lagging strand. The strands are complementary rather than identical, and they are held together by hydrogen bonds.