What are the components of a nucleotide and which base pairs with which?

• A. A sugar, phosphate, and nitrogenous base; A pairs with T and C with G
• B. A sugar, phosphate, and nitrogenous base; A pairs with C and G with T
• C. A sugar, fatty acid, and base; A with T and G with C
• D. A sugar, phosphate, and base; A pairs with G and C with T

Answer: (A)

Nucleotides are made of three parts: a sugar, a phosphate group, and a nitrogenous base. In DNA, the sugar is deoxyribose, and the bases pair across the two strands in a specific way: adenine pairs with thymine, and cytosine pairs with guanine. This pairing, based on hydrogen bonding, keeps the DNA double helix uniform in width and enables accurate replication. The correct option reflects both the components of a nucleotide and the proper base-pairing rules: A with T and C with G.