Which statement correctly describes the components of a nucleotide and how nucleotides are linked to form nucleic acids?

• A. A nucleotide consists of a sugar, a phosphate, and a base; linked by glycosidic bonds between sugar and base.
• B. A nucleotide consists of a ribose sugar, a phosphate group, and a nitrogenous base; linked by phosphodiester bonds between the 3' hydroxyl of one sugar and the 5' phosphate of the next.
• C. A nucleotide consists of a deoxyribose sugar, a phosphate, and a nitrogenous base; linked by hydrogen bonds between nucleotides.
• D. A nucleotide consists of a deoxyribose sugar, a phosphate group, and a nitrogenous base; linked by phosphodiester bonds between the 3' hydroxyl of one sugar and the 5' phosphate of the next.

Answer: (D)

Nucleotides are made of three parts: a sugar (deoxyribose in DNA), a phosphate group, and a nitrogenous base. The sugar and phosphate form the backbone, with phosphodiester bonds linking them: the 3' hydroxyl of one sugar reacts with the 5' phosphate of the next nucleotide, creating a chain that runs in the 5' to 3' direction. The base sits attached to the sugar inside the nucleotide itself via an N-glycosidic bond, not involved in linking nucleotides together. Hydrogen bonds can hold two DNA strands together between bases, but they don’t link nucleotides within a single strand.

This is why the description with deoxyribose, a phosphate, and a base, and linking by phosphodiester bonds between the 3' hydroxyl and the 5' phosphate is the correct description. The other statements miss key aspects: linking nucleotides with glycosidic bonds is incorrect for polymer formation; using ribose describes RNA rather than DNA; and hydrogen bonds do not connect nucleotides in a single strand.