DNA's shape is described as a double what?

DNA's shape is described as a double what?

• A. Alpha helix
• B. Double helix
• C. Beta sheet
• D. Random coil

Answer: (B)

DNA's shape is a double helix. It consists of two long polynucleotide strands wound around each other, with the sugar–phosphate backbones on the outside and the bases paired inside the helix. The strands run in opposite directions (antiparallel) and twist in a right-handed manner in the common form, giving the characteristic double-helix appearance. This structure explains how genetic information is stored and faithfully copied: bases pair specifically—adenine with thymine via two hydrogen bonds, and guanine with cytosine via three—holding the two strands together and enabling accurate replication. The other terms describe protein structures or unstructured regions, not DNA: an alpha helix and a beta sheet are protein secondary structures, while a random coil refers to a lack of defined structure. That’s why “double helix” is the best descriptor for DNA’s shape.

DNA's shape is a double helix. It consists of two long polynucleotide strands wound around each other, with the sugar–phosphate backbones on the outside and the bases paired inside the helix. The strands run in opposite directions (antiparallel) and twist in a right-handed manner in the common form, giving the characteristic double-helix appearance. This structure explains how genetic information is stored and faithfully copied: bases pair specifically—adenine with thymine via two hydrogen bonds, and guanine with cytosine via three—holding the two strands together and enabling accurate replication. The other terms describe protein structures or unstructured regions, not DNA: an alpha helix and a beta sheet are protein secondary structures, while a random coil refers to a lack of defined structure. That’s why “double helix” is the best descriptor for DNA’s shape.