What is the shape of DNA?

• A. Spiral ladder
• B. Helix
• C. Double helix
• D. Chromosome

Answer: (C)

DNA is in the form of a double helix. This means two long strands of nucleotides run in opposite directions and twist around a common axis, forming two intertwined helices. The sugar–phosphate backbones lie on the outside, while the bases pair up inside the structure (A with T, and G with C), creating the rungs of a twisted ladder. The two strands are complementary and antiparallel, and their right-handed twist is the typical form in many organisms. This arrangement not only compactly stores genetic information but also provides a straightforward template for copying the sequence during replication. Describing it as a spiral ladder is a partial image, but it misses that there are two strands; calling it a simple helix describes only one strand, and a chromosome refers to a larger, organized structure that contains DNA, not the shape of the DNA molecule itself.