Purines and pyrimidines are two types of nitrogenous bases found in nucleic acids (DNA and RNA).
They differ in structure, size, and the types of bases they include.
Here’s a explanation:
1. Structure and Size:
- Purines have two rings in their chemical structure — a double-ring (one six-membered and one five-membered ring).
- Pyrimidines have only one ring — a single six-membered ring.
So, purines are larger molecules, while pyrimidines are smaller.
2. Types Found in DNA and RNA:
- Purines:
- Adenine (A)
- Guanine (G)
(Found in both DNA and RNA)
- Pyrimidines:
- Cytosine (C) — in both DNA and RNA
- Thymine (T) — only in DNA
- Uracil (U) — only in RNA (replaces thymine)
3. Base Pairing:
- Purines always pair with pyrimidines to keep the DNA structure even:
- Adenine (a purine) pairs with Thymine (a pyrimidine) in DNA.
- Guanine (a purine) pairs with Cytosine (a pyrimidine) in both DNA and RNA.
- In RNA, Adenine pairs with Uracil instead of Thymine.
4. Function:
- Both purines and pyrimidines store genetic information by forming the “letters” (bases) of the DNA and RNA code.
- Their pairing ensures stability and accurate replication of the genetic material.
In short:
- Purines = large, double-ring bases (A and G)
- Pyrimidines = small, single-ring bases (C, T, and U)
- Together, they form the base pairs (A–T / A–U and G–C) that make up the genetic code in DNA and RNA.