1. Introduction
Purines are heterocyclic diureides (having two urea residues) aromatic organic compounds. They consist of a pyrimidine ring fused to an imidazole ring. Purines are the most widely occurring nitrogen-containing heterocycles in nature and serve as critical building blocks for nucleic acids (DNA and RNA).
2. Properties
- Solubility: Generally poorly soluble in cold water but more soluble in hot water.
- Basicity: They act as weak bases due to the nitrogen atoms in the ring structure.
- Melting Point: 212-213 °C.
- UV Absorption: Purines exhibit strong absorption of ultraviolet light, typically around 260 nm, which is useful for laboratory quantification.
3. Synthesis
Purines are synthesized in the body via the de novo pathway, primarily in the liver. The process involves building the purine ring directly onto a ribose-5-phosphate backbone using amino acids (glycine, glutamine, and aspartate), carbon dioxide, and N10-formyltetrahydrofolate.
Read Synthesis of Purine
4. Classification
Purines can be classified based on their biological role:
- Nucleobases: The primary components of DNA/RNA (Adenine and Guanine).
- Nucleosides: A purine base attached to a sugar (e.g., Adenosine, Guanosine).
- Nucleotides: A nucleoside with a phosphate group (e.g., ATP, GTP).
The natural purines are either the hydroxy or amino derivatives of the parent substance purine and hence they may be classified into two groups
- Hydroxy or Oxy-purines: These are the hydroxy derivatives of the purine and possess the following types of grouping.
-C(OH)=N- ⇌ -(C=O)-NH- - Aminopurines: The amino derivatives of purines are found in each and every living cell in the form of nucleic acids.
Examples: Uric acid, Xanthine and Hypoxanthine
Examples: Adenine and Guanine
5. Different Purines
While Adenine and Guanine are the most famous biological purines, the family includes several other derivatives:
- Adenine: Pairs with Thymine in DNA.
- Guanine: Pairs with Cytosine in DNA.
- Hypoxanthine: A naturally occurring purine derivative.
- Xanthine: An intermediate in purine degradation.
- Uric Acid: The final oxidation product of purine metabolism in humans.