Final answer:
The structure of DNA is a double helix with a sugar-phosphate backbone and bases projecting inside, where adenine pairs with thymine and guanine with cytosine, and the strands run antiparallel to each other.
Step-by-step explanation:
The structure of a DNA molecule can best be described as composed of a sugar-phosphate backbone with bases projecting towards the inside of the backbone. This accurately reflects the double helical structure where nucleotides consisting of a 5 carbon sugar (deoxyribose), a phosphate group, and a nitrogenous base are bonded together. Complementary base pairing occurs between the strands with adenine pairing with thymine and guanine pairing with cytosine. Adenine and thymine form two hydrogen bonds while cytosine and guanine form three hydrogen bonds. The strands run antiparallel to each other, meaning they run in opposite directions. This structure allows for the stable formation of the iconic double helix of DNA.