What structural features did Watson and Crick propose for DNA in 1953?

What structural features did Watson and Crick propose for DNA in 1953?

• A. A single helix with parallel strands.
• B. A quadruple helix.
• C. A double helix with two antiparallel strands and complementary base pairing.
• D. A triple helix with random pairing.

Answer: (C)

The main idea is that DNA is two long polynucleotide chains wound into a right-handed double helix, with the sugar-phosphate backbones on the outside and the bases paired on the inside. The two strands run in opposite directions (antiparallel), which is crucial for how enzymes read the template during replication. Bases pair specifically: adenine pairs with thymine and guanine pairs with cytosine, connected by hydrogen bonds. This complementary base pairing gives the molecule a uniform diameter and a stable structure, and it also means each strand can serve as a template to copy its partner, driving accurate semi-conservative replication. The pairing pattern also explains Chargaff’s rules, where A pairs with T and G with C.

The main idea is that DNA is two long polynucleotide chains wound into a right-handed double helix, with the sugar-phosphate backbones on the outside and the bases paired on the inside. The two strands run in opposite directions (antiparallel), which is crucial for how enzymes read the template during replication. Bases pair specifically: adenine pairs with thymine and guanine pairs with cytosine, connected by hydrogen bonds. This complementary base pairing gives the molecule a uniform diameter and a stable structure, and it also means each strand can serve as a template to copy its partner, driving accurate semi-conservative replication. The pairing pattern also explains Chargaff’s rules, where A pairs with T and G with C.