Which components make up a DNA nucleotide?

• A. A phosphate, sugar, and a nitrogen base
• B. A phosphate, lipid, and a sugar
• C. A sugar, a protein, and a sugar
• D. A base, a lipid, and a phosphate

Answer: (A)

DNA nucleotides are built from three parts: a phosphate group, a five-carbon sugar (deoxyribose in DNA), and a nitrogenous base. The sugar and phosphate form the repeating backbone of the DNA strand through phosphodiester bonds, while the nitrogenous base sticks off the sugar and encodes genetic information. The phosphate group also provides the linkage that connects one nucleotide to the next, creating a long polymer. The other options mix in components that are not part of a nucleotide—lipids or proteins are separate biomolecules, and having two sugars or a lipid with the phosphate would not constitute a nucleotide. So the essential trio—phosphate, sugar, and a nitrogen base—correctly identifies the components of a DNA nucleotide.