1. Purine bases
- Adenine (A)
- Guanine (G)
- Structure: Two fused rings.
2. Pyrimidine bases
- Cytosine (C)
- Thymine (T)
- Uracil (U)
- Structure: One ring.
Important facts for JEE/NEET
| DNA | RNA |
|---|---|
| Adenine (A) | Adenine (A) |
| Guanine (G) | Guanine (G) |
| Cytosine (C) | Cytosine (C) |
| Thymine (T) | Uracil (U) |
Memory trick:
- Purines: A and G — Pure As Gold
- Pyrimidines: C, T and U
Exam point: Purines have a double-ring structure, whereas pyrimidines have a single-ring structure.
