The two strands of a DNA double helix are antiparallel, meaning one runs 5' to 3' and the other runs:

1. Antiparallel describes two strands running alongside each other in opposite directions. 2. One strand runs in the 5 prime to 3 prime direction. 3. The complementary strand runs in the 3 prime to 5 prime direction. 4. The carbon atoms of the five-carbon sugar are numbered 1 prime through 5 prime, so 1 prime and 2 prime are not strand directions. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 14 'DNA Structure and Function', sections 14.1-14.6_