Which description best captures the structure of DNA components?

• A. A sugar-phosphate backbone with nitrogen bases projected into the interior of each helix
• B. A sugar-phosphate backbone with bases exposed on the exterior
• C. A sugar-phosphate backbone with nitrogen bases on the exterior
• D. A lipid envelope surrounding a protein core

Answer: (A)

DNA is built as a double helix with the sugar-phosphate backbone forming the outer rails, while the nitrogenous bases are tucked toward the interior and pair with the complementary bases on the opposite strand. This arrangement keeps the bases inside the helix, enabling specific base pairing and stable replication. The description that matches this structure is the one where the backbone is on the outside and the bases project inward. The other options misplace the bases on the exterior or introduce a lipid envelope, which does not describe DNA’s actual architecture.