DNA/RNA Base Reference
Nucleic acid building blocks: bases, base pairing, nucleotide structure, and DNA vs RNA comparison.
The 5 Nitrogenous Bases
A purine base that pairs with thymine in DNA and uracil in RNA via two hydrogen bonds. Contains a fused pyrimidine-imidazole ring system.
A purine base that pairs with cytosine via three hydrogen bonds, making G-C pairs stronger than A-T pairs. Contains a carbonyl group at C-6.
A pyrimidine base that pairs with guanine via three hydrogen bonds. Subject to spontaneous deamination to uracil, a common source of point mutations.
A pyrimidine base exclusive to DNA. Pairs with adenine via two hydrogen bonds. Distinguished from uracil by a methyl group at C-5, which protects against misincorporation errors.
A pyrimidine base exclusive to RNA. Replaces thymine and pairs with adenine via two hydrogen bonds. Lacks the C-5 methyl group present in thymine.
Base Pairing Rules (Watson-Crick)
Adenine pairs with thymine through 2 hydrogen bonds (one N–H···O, one N–H···N)
Adenine pairs with uracil through 2 hydrogen bonds (same pattern as A–T pairing)
Guanine pairs with cytosine through 3 hydrogen bonds (two N–H···O, one N–H···N), the strongest Watson–Crick pair
Nucleotide Structure
A nucleotide is the monomer unit of nucleic acids, composed of three parts: a nitrogenous base, a five-carbon sugar, and one or more phosphate groups. In DNA the sugar is 2′-deoxyribose (lacking the 2′-hydroxyl group); in RNA it is ribose. The phosphate group connects the 5′-carbon of one sugar to the 3′-carbon of the next via phosphodiester bonds, forming the sugar-phosphate backbone.
DNA vs RNA Comparison
| Feature | DNA | RNA |
|---|---|---|
| Full Name | Deoxyribonucleic acid | Ribonucleic acid |
| Sugar | Deoxyribose (2′-H) | Ribose (2′-OH) |
| Bases | A, G, C, T | A, G, C, U |
| Structure | Double-stranded helix | Usually single-stranded |
| Primary Function | Long-term genetic storage | Gene expression, regulation, catalysis |
| Location | Nucleus (eukaryotes), nucleoid (prokaryotes) | Nucleus, cytoplasm, ribosomes |
| Stability | More stable (no 2′-OH) | Less stable (2′-OH susceptible to hydrolysis) |
| Replication | Self-replicating | Synthesized from DNA template |