What is the chemical composition of DNA?

The correct answer is that DNA has an alternating sugar-phosphate backbone. This structure is fundamental to the identity and function of DNA. The backbone consists of repeating units of deoxyribose sugar and phosphate groups, which are linked together by covalent bonds. This configuration provides structural stability to the DNA molecule.

In addition to the sugar-phosphate backbone, DNA also contains nitrogenous bases (adenine, thymine, cytosine, and guanine) that pair in specific ways to form the double helix structure. However, the focus of the question is on the chemical composition that describes the backbone itself, which is essential for the overall structure and function of DNA, allowing it to carry genetic information.

The other options refer to components of biological molecules that do not accurately describe DNA. Proteins are made of amino acids, not part of the DNA structure, while carbohydrates and vitamins do not relate to DNA composition. Additionally, DNA does not consist of amino acids; those are the building blocks of proteins, which serve different roles in the cell.