Question

In the DNA double helix, what is the directional orientation of the two antiparallel polynucleotide chains?

Options

• Both strands run 5′→3′

• One strand runs 5′→3′ and the complementary strand runs 3′→5′

• Both strands run 3′→5′

• One strand runs 3′→5′ and the other runs 5′→3′ but they are parallel

Answer 1

The two polynucleotide chains in the DNA double helix are antiparallel, meaning they run in opposite directions. One strand runs from the 5′ (five-prime) end to the 3′ (three-prime) end, while the complementary strand runs in the opposite direction from 3′ to 5′. This antiparallel arrangement is one of the five salient features of the Watson-Crick double helix model.