Difference Between Purine and Pyrimidine

Purine vs Pyrimidine

Nucleic acids are macro molecules formed by the combination of thousands of nucleotides. They have C, H, N, O, and P. There are two types of nucleic acids in biological systems as DNA and RNA. They are the genetic material of an organism and are responsible for passing genetic characteristics from generation to generation. Further, they are important to control and maintain cellular functions. A nucleotide is composed of three units. There is a pentose sugar molecule, a nitrogenous base and a phosphate group. There are mainly two groups of nitrogenous bases as purines and pyrimidines. They are heterocyclic organic molecules. Cytosine, thymine, and uracil are examples for pyrimidine bases. Adenine and guanine are the two purine bases. DNA has adenine, Guanine, cytosine, and thymine bases, whereas RNA has A, G, C, and uracil (instead of thymine). In DNA and RNA, complimentary bases form hydrogen bonds between them. That is adenine: thiamine/ uracil and guanine: cytosine are complimentary to each other.

Purine

Purine is an aromatic organic compound. It is a heterocyclic compound containing nitrogen. In purine, a pyrimidine ring and a fused imidazole ring are present. It has the following basic structure.

Purines and their substituted compounds are widely distributed in nature. They are present in nucleic acid. Two purine molecules, adenine and guanine, are present in both DNA and RNA. Amino group and a ketone group are attached to the basic purine structure to make adenine and guanine. They have the following structures.

In nucleic acids, purine groups make hydrogen bonds with complementary pyrimidine bases. That is adenine makes hydrogen bonds with thymine and guanine makes hydrogen bonds with cytosine. IN RNA, since thymine is absent, adenine makes hydrogen bonds with uracil. This is called complementary base pairing which is crucial for nucleic acids. This base pairing is important for living beings for evolution.

Other than these purines, there are many other purines like xanthine, hypoxanthine, uric acid, caffeine, isoguanine, etc. Other than in nucleic acids, they are found in ATP, GTP, NADH, coenzyme A, etc. There are metabolic pathways in many organisms to synthesize and breakdown purines. Defects in enzymes in these pathways can cause severe effects on humans like causing cancer. Purines are abundant in meat and meat products.

Pyrimidine

Pyrimidine is a heterocyclic aromatic compound. It is similar to benzene except pyrimidine has two nitrogen atoms. The nitrogen atoms are at 1 and 3 positions in the six member ring. It has the following basic structure.

Pyrimidine has common properties with pyridine. Nucleophilic aromatic substitutions are easier with these compounds than electrophilic aromatic substitutions due to the presence of nitrogen atoms. The pyrimidines found in nucleic acids are substituted compounds of the basic pyrimidine structure.

There are three pyrimidine derivatives found in DNA and RNA. Those are cytosine, thymine, and uracil. They have the following structures.

What is the difference between Purine and Pyrimidine?

• Pyrimidine has one ring and purine has two rings.

• Purine has a pyrimidine ring and an imidazole ring.

• Adenine and guanine are the purine derivative present in nucleic acids whereas cytosine, uracil and thymine are the pyrimidine derivatives present in the nucleic acids.

• Purines have more intermolecular interactions than pyrimidines.

• Melting points and boiling points of purines are much higher compared to pyrimidines.