Which statement below correctly identifies the base-pairs in DNA?

• A. Hydrogen bonding allows A with C and G with T
• B. Covalent bonds join A with T and G with C
• C. DNA replication occurs in the cytoplasm
• D. The sugar-phosphate backbone is formed by covalent bonds between sugar and phosphate

Answer: (D)

DNA’s structure hinges on two key bonded features: covalent bonds form the sugar–phosphate backbone of each strand, and hydrogen bonds hold the complementary base pairs together between the two strands. The statement about the sugar–phosphate backbone being formed by covalent bonds between sugar and phosphate correctly describes how DNA’s backbone is built. This is the most accurate description among the options, as it reflects a fundamental, true aspect of DNA’s architecture.

The other statements mix up important concepts: base pairing occurs between adenine and thymine, and between cytosine and guanine, via hydrogen bonds—not covalent bonds; the pairing A–C or G–T is incorrect. Base pairing chemistry and the backbone chemistry are different kinds of connections, and DNA replication is not confined to the cytoplasm in eukaryotes.