Table of Contents
What are Purines and Pyrimidines ?
Purines and pyrimidines are organic compounds found in DNA and RNA. Purines are composed of two fused rings, and pyrimidines are composed of one fused ring. These molecules are important for the structure and function of DNA and RNA.
Structure of Purine and Pyrimidine
The basic structure of purine and pyrimidine is a six-carbon ring with four nitrogen atoms. The nitrogen atoms can be in any of the five different positions, which gives rise to the many different possible structures of these molecules.
Difference Between Purine and Pyrimidine
Purines and pyrimidines are two types of nitrogenous bases that make up the nucleotides of DNA and RNA. Purines are composed of two fused rings, while pyrimidines are composed of one fused ring.
The most important difference between purines and pyrimidines is that purines can be converted into uric acid, while pyrimidines cannot. Uric acid is a waste product that can cause kidney stones and gout if it builds up in the body.
Purine Catabolism
Purine metabolism is the process by which purine nucleotides are degraded to uric acid. Purine nucleotides are the building blocks of DNA and RNA. The degradation of purine nucleotides to uric acid is a two step process. The first step is the conversion of purine nucleotides to IMP (inosine monophosphate). The second step is the conversion of IMP to uric acid.
The conversion of purine nucleotides to IMP is catalyzed by the enzyme inosine monophosphate dehydrogenase (IMPDH). The conversion of IMP to uric acid is catalyzed by the enzyme urate oxidase (urate oxidase is also called uricase).
Conversion of Base to Uric Acid
When the body breaks down purines, it produces uric acid. The kidneys help to control the level of uric acid in the blood by removing excess amounts from the blood and excreting it in the urine. When the kidneys cannot remove enough uric acid from the blood, the level of uric acid in the blood rises and this can cause kidney stones and gout.
Pyrimidine Catabolism
The catabolism of pyrimidines can be summarized as follows:
The pyrimidine ring is opened by a pyrimidine dimerase enzyme, which produces two molecules of uracil.
Uracil is then converted to thymine by a uracil phosphoribosyltransferase enzyme.
Thymine is then converted to 5-methyluracil by a thymine methyltransferase enzyme.
5-methyluracil is then converted to thymine by a 5-methyluracil dehydrogenase enzyme.
