Which statement best describes the basic structural features of DNA?

• A. Right-handed double helix with antiparallel strands
• B. Left-handed single helix with parallel strands
• C. Triple helix with identical strands
• D. Circular molecule with no grooves

Answer: (A)

The basic feature being tested is the canonical form of DNA: a right-handed double helix with two sugar-phosphate backbones that run in opposite directions (antiparallel). In this arrangement, bases pair across the interior (A with T, G with C) to stabilize the structure, and the helix presents major and minor grooves that proteins recognize during replication and transcription. The “right-handed” aspect corresponds to the common B-DNA form found in cells, while the strands being antiparallel is crucial for accurate base pairing and the directional synthesis of new DNA strands. The other descriptions—left-handed single helix, triple helix, or circular molecule with no grooves—do not match the standard DNA architecture encountered in most biological contexts.