Read DNA and RNA by Their Bonds and Bases
Nucleic-acid questions test the backbone, base–sugar linkage, complementary pairing and how pairing suggests copying.
Chemistry questions first require the material, particles or reaction condition to be identified before a formula or rule is selected.
Separate the bonds
Nucleotides in one strand join by 3′–5′ phosphodiester bonds; each nitrogenous base attaches to its sugar by an N-glycosidic bond. In double-stranded DNA, each strand with n nucleotides has n−1 backbone bonds.
Compare DNA and RNA
Both have phosphate backbones. DNA uses deoxyribose and thymine; RNA uses ribose and uracil. A–T forms two hydrogen bonds and G–C three. Complementary base pairing suggested how a strand could guide its copy.
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- ✓Base–sugar: glycosidic; nucleotide–nucleotide: phosphodiester.
- ✓Each linear strand has one fewer phosphodiester bond than nucleotides.
- ✓A–T: 2 bonds; G–C: 3 bonds.
A base is not attached to sugar by a phosphodiester bond.
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