Purines and Pyrimidines

Introduction:

Purines and Pyrimidines are aromatic heterocyclic organic nitrogen compounds and they are the very essential components of the nucleic acids.

Purines

Purines are aromatic heterocyclic compound containing two rings. One is pyrimidine ring and another one is imidazole ring, they both fused to form purine. Some notable purines are:

• Adenine
• Guanine
• Xanthine
• Hypoxanthine
• Theobromine
• Isoguanine
• Uric acid
• Caffeine.

Nearly 50% of the purines found in earth are the constituents of nucleic acids. Some chemical properties of purines are:

• Molecular formula C₅H₄N₄ 
• Molar mass - 120.1
• Melting point - 214 degree Celsius.

Pyrimidines

Pyrimidines are aromatic heterocyclic compound consists of only one ring which is a part of purine. Structure of pyrimidine resembles the structure of benzene and pyridine. Some notable pyrimidines are

• Cytosine
• Thymine
• Uracil

All of them found in nucleic acids. Chemical properties of pyrimidines:

• Molecular formula  C₅H₄N₄ 
• Molar mass - 80.08
• Melting point: 20 - 22 degree Celsius
• Boiling point: 123 -124 degree Celsius.

Purines and Pyrimidines are the constituents of nucleic acids:

Both of them are the important constituents of nucleic acids. Most of the purines and pyrimidines are existed in the form of nucleoside. Nucleoside is formed by the combination of either purine or pyrimidine with pentose sugar. Pentose sugar such as deoxyribose sugar in DNA and ribose sugar in RNA. Then, nucleotides are formed when these nucleosides combined with phosphoric acid.

Some of the nucleotides according to nitrogenous base present are:

• Adenosine monophosphate,
• Guanosine monophosphate
• Cytosine monophosphate,
• Thymosine monophosphate,

These monophosphate forms are also available in the form of di & tri phosphates

These nucleotides are grouped together to form polynucleotide chain. When two strands of polynucleotide chain combined to form DNA. When it combined, it forms as a double helical structure.

Two polynucleotide chains bonded together by hydrogen bonds. But in most RNA, only single strand is there. The difference between DNA and RNA in their composition is replacement of thymine by uracil in RNA.