Question

In a DNA double helix, what is the spatial relationship between the two polynucleotide strands?

Options

• The two strands run parallel in the same 3′→5′ direction

• The two strands run parallel in the same 5′→3′ direction

• The orientation of the strands is random and variable

• The two strands are antiparallel, with one running 5′→3′ and the other 3′→5′

Answer 1

In a DNA double helix, the two strands are antiparallel, meaning they run in opposite directions. One strand runs from 5′ to 3′, while the complementary strand runs from 3′ to 5′. This antiparallel arrangement is essential for the proper pairing of nitrogenous bases through hydrogen bonds.