What is the structure of DNA?

• A. Double Helix
• B. Single Strand
• C. Triple Helix
• D. Circular

Answer: (A)

DNA is a double helix: two long polymer chains of nucleotides run in opposite directions (antiparallel) and twist around each other. The sugar–phosphate backbone forms the sides of a ladder, while the bases pair across the two strands (A with T, G with C) to form the rungs through hydrogen bonds. This arrangement enables precise replication, because each strand serves as a template for creating a new complementary strand, yielding semi-conservative replication. The double-helix structure is stabilized by base stacking and hydrophobic interactions inside the helix, and the major and minor grooves provide binding sites for proteins involved in transcription and replication. The other options don’t fit the standard organization: a single strand lacks complementary pairing, a triple helix isn’t the typical form in cells, and circular DNA occurs in some organisms but the canonical structure is a double helix.