Final answer:
The correct answer is that in double-stranded DNA, the two strands are complementary and anti-parallel in their orientation. Complementary base pairing includes A with T and C with G, and the strands run in opposite directions to each other.
Step-by-step explanation:
In double-stranded DNA, the two strands are complementary in their base sequences and anti-parallel in their orientation. Complementary means that the nucleotides of one strand match up with the nucleotides of the other strand in a specific way: adenine pairs with thymine (A=T), and cytosine pairs with guanine (C=G). This base pairing is due to their shape, size, and hydrogen bonding capabilities. The anti-parallel orientation refers to the direction in which the two strands run relative to each other; one strand runs in a 5' to 3' direction, while the other runs in a 3' to 5' direction.
The structure of DNA is often described as a twisted ladder or double helix. The side rails of the ladder are composed of alternating sugar and phosphate groups, while the steps or rungs of the ladder are the nitrogenous bases paired and bonded across the two strands. The strands are held together through hydrogen bonds, not di-sulfide bonds, which stabilize the double helix structure.