1. Structure:
* Purines (double-ringed): Adenine (A) and Guanine (G) have a double-ring structure consisting of a pyrimidine ring fused to an imidazole ring.
* Pyrimidines (single-ringed): Cytosine (C), Thymine (T), and Uracil (U) have a single-ring structure.
2. Chemical Composition:
* Adenine (A): Consists of a purine base with an amino group at position 6.
* Guanine (G): Consists of a purine base with an amino group at position 2 and an oxo group at position 6.
* Cytosine (C): Consists of a pyrimidine base with an amino group at position 4 and an oxo group at position 2.
* Thymine (T): Consists of a pyrimidine base with a methyl group at position 5, an amino group at position 4, and two oxo groups at positions 2 and 4.
* Uracil (U): Consists of a pyrimidine base with an amino group at position 4 and two oxo groups at positions 2 and 4. It's essentially a demethylated form of thymine.
3. Pairing:
* Adenine (A) pairs with Thymine (T) in DNA via two hydrogen bonds.
* Adenine (A) pairs with Uracil (U) in RNA via two hydrogen bonds.
* Guanine (G) pairs with Cytosine (C) in both DNA and RNA via three hydrogen bonds.
4. Role:
* DNA: Adenine, Guanine, Cytosine, and Thymine are the building blocks of DNA, forming the genetic code for all living organisms.
* RNA: Adenine, Guanine, Cytosine, and Uracil are the building blocks of RNA, which plays a crucial role in protein synthesis and other cellular functions.
Key Differences between Thymine and Uracil:
* Methyl Group: The only difference between Thymine and Uracil is the presence of a methyl group at position 5 in Thymine.
* Location: Thymine is found exclusively in DNA, while Uracil is found exclusively in RNA.
In Summary: The five nitrogenous bases differ in their structure, chemical composition, and pairing properties, which directly contribute to their distinct roles in DNA and RNA.
