In DNA structure, the two strands run in opposite directions, a property known as what?

In DNA structure, the two strands run in opposite directions, a property known as what?

• A. Antiparallel
• B. Parallel
• C. Complementary
• D. Helical

Answer: (A)

Antiparallel arrangement describes the orientation of the two DNA strands: they run in opposite directions, with one 5′ to 3′ and the other 3′ to 5′. This opposite directionality is crucial because DNA polymerases can only add nucleotides to the 3′ end, so copying both strands requires one template read in each direction. It explains why replication occurs with a leading strand synthesized continuously in the 5′ to 3′ direction and a lagging strand made in short fragments. The term complementary refers to base pairing between strands, not their directional arrangement, and helix describes the overall shape, not the direction of each strand. Parallel would imply the strands run in the same direction, which isn’t the case.

Antiparallel arrangement describes the orientation of the two DNA strands: they run in opposite directions, with one 5′ to 3′ and the other 3′ to 5′. This opposite directionality is crucial because DNA polymerases can only add nucleotides to the 3′ end, so copying both strands requires one template read in each direction. It explains why replication occurs with a leading strand synthesized continuously in the 5′ to 3′ direction and a lagging strand made in short fragments. The term complementary refers to base pairing between strands, not their directional arrangement, and helix describes the overall shape, not the direction of each strand. Parallel would imply the strands run in the same direction, which isn’t the case.