𧬠Purines: Definition
Purines are a class of organic molecules that serve as building blocks for nucleic acids (DNA and RNA). They are characterized by a double-ring structure, which distinguishes them from pyrimidines. The two major purines found in nucleic acids are adenine (A) and guanine (G).
- βοΈ Purines consist of a double-ring structure: a six-membered ring fused to a five-membered ring.
- 𧬠Adenine (A) and Guanine (G) are the two purines found in DNA and RNA.
- π§ͺ Purines are synthesized through a complex metabolic pathway involving several enzymes.
π§ͺ Pyrimidines: Definition
Pyrimidines are also organic molecules that serve as building blocks for nucleic acids. Unlike purines, pyrimidines have a single-ring structure. The three pyrimidines found in nucleic acids are cytosine (C), thymine (T) (found in DNA), and uracil (U) (found in RNA).
- βοΈ Pyrimidines consist of a single six-membered ring structure.
- 𧬠Cytosine (C), Thymine (T) (in DNA), and Uracil (U) (in RNA) are the three pyrimidines.
- π§ͺ Pyrimidines are also synthesized through a metabolic pathway, different from that of purines.
π¬ Purines vs. Pyrimidines: A Detailed Comparison
| Feature |
Purines |
Pyrimidines |
| Ring Structure |
Double-ring (a six-membered ring fused to a five-membered ring) |
Single-ring (a six-membered ring) |
| Nitrogen Atoms |
Four nitrogen atoms |
Two nitrogen atoms |
| Common Examples |
Adenine (A), Guanine (G) |
Cytosine (C), Thymine (T), Uracil (U) |
| Occurrence in Nucleic Acids |
Found in both DNA and RNA |
Found in both DNA and RNA |
| Base Pairing |
Adenine (A) pairs with Thymine (T) in DNA, and Adenine (A) pairs with Uracil (U) in RNA; Guanine (G) pairs with Cytosine (C) in both DNA and RNA |
Cytosine (C) pairs with Guanine (G) in both DNA and RNA; Thymine (T) pairs with Adenine (A) in DNA, and Uracil (U) pairs with Adenine (A) in RNA |
| Molecular Weight |
Higher molecular weight due to double-ring structure |
Lower molecular weight due to single-ring structure |
π Key Takeaways
- 𧬠Purines have a double-ring structure, while pyrimidines have a single-ring structure.
- π§ͺ Adenine (A) and Guanine (G) are purines; Cytosine (C), Thymine (T), and Uracil (U) are pyrimidines.
- π‘ In DNA, A pairs with T, and G pairs with C. In RNA, A pairs with U, and G pairs with C. This is based on the number of hydrogen bonds each can form: A-T/U have two, and G-C have three.
- π’ The difference in ring structure and composition affects their molecular weight and synthesis pathways.