What forms the backbone of DNA?

The backbone of DNA is composed of alternating units of a sugar molecule called deoxyribose and phosphate groups. In each DNA strand, the deoxyribose sugar is connected to a phosphate group, forming a repeating sugar-phosphate backbone. This structure gives DNA its stability and form, allowing it to maintain the double helical structure essential for genetic information storage.

In this context, while deoxyribose and the nitrogenous bases are components of DNA, the bases do not make up the backbone; instead, they project from the sugar-phosphate backbone and are responsible for base pairing. Additionally, ribose is found in RNA, not DNA, which makes the third option incorrect. Amino acids, which are building blocks of proteins, do not play a role in forming the structure of DNA, making that option irrelevant as well. Therefore, the correct composition of the DNA backbone is indeed the pentose sugar deoxyribose and the phosphate groups.