The two DNA chains in a double helix ______ .
A)have an overall diameter of 2 µm
B)have identical base sequences
C)are held together due to the charges of their phosphate groups
D)wind around each other in such a way that purines are always opposite pyrimidines and vice versa
E)are parallel to each other in 5' to 3' directionality

Question

Quizplus · Accepted Answer

The two DNA chains wind around each other in a double helix in such a way that purines (adenine and guanine) are always opposite pyrimidines (thymine and cytosine) and vice versa. This is known as complementary base pairing and allows for the hydrogen bonding between the bases to hold the two strands together. The overall diameter of the DNA double helix is about 2 nanometers (not micrometers), the base sequences are complementary but not necessarily identical, and the charges on the phosphate groups do play a role in DNA structure but are not the sole reason for the two strands being held together. The DNA strands are antiparallel, meaning they run in opposite 5' to 3' directions.

The Two DNA Chains in a Double Helix ______