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Purine bases are adenine and guanine having two carbon-nitrogen rings.

What are Purines and Pyrimidines  The nucleotide bases in DNA and RNA include nitrogenous bases in the form of purines and pyrimidines. Purine bases are adenine and guanine having two carbon-nitrogen rings. On the other hand, pyrimidine bases such as cytosine and thymine have one carbon-nitrogen ring. Structure of Purine and Pyrimidine 

The structure of purine is largely heterocyclic with the aromatic compound comprising four nitrogen atoms. Two carbon rings are also present. These rings are made up of a fusion of imidazole ring and pyrimidine. [Image will be Uploaded Soon]

Pyrimidine is heterocyclic in nature with the aromatic compound only consisting of one carbon ring and two nitrogen atoms. [Image will be Uploaded Soon] This inherent structure of the bases leads to purine and pyrimidine difference. Do You Know? The identification of pyrimidine compounds took a long time. Even though its isolation took place somewhere within 1837 and 1864, the recognition of its structures did not come through till 1868. Nucleobases  Purine composes two out of four nucleobases both in deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) –

[Images will be Uploaded Soon] Pyrimidines consist of the remaining bases in DNA and RNA –

[Images will be Uploaded Soon] Function of Purine and Pyrimidine Bases 

Owing to the end-product of purine catabolism being uric acid, it has a significant role to play in our body. The urate oxidase enzyme is not present in the human body, and from uric acid, urate is created. Formation of uric acid takes place in the liver and subsequently discharged with urine through the kidney. In the human body, monosodium salt and un-dissociated uric acid are least soluble. Such nature usually does not cause any problem in the human body unless urine has very high acidic content. Concentration of urate eventually causes the development of gout.

Pyrimidine catabolism leads to the end-product of carbon dioxide, ammonia and beta-amino acids. The beta-amino acid is mostly excreted, otherwise it is incorporated into muscle dipeptides. The difference between purine and pyrimidine are the following –

Now that you have a basic understanding of the bases as well as the difference between pyrimidine and purine, challenge yourself by solving the following! Test Yourself 

(a) Nitrogen bases + Pentose sugar + Phosphate (b) Nitrogen bases + Pentose sugar (c) Purine bases (d) None of the above

(a) Uracil (b) Thymine (c) Cytosine (d) Adenosine [To check your answer, see the solution mentioned at the end of the article]    

Ans. Purines and pyrimidines undertake the same function, that is providing energy to cells and necessary for the production of DNA and RNA along with starch, protein and regulation of enzymes.

Ans. Purines are bigger in size than pyrimidines as the former is a two-ringed structure as opposed to a structure with one ring.

Ans. There is a pairing between pyrimidine and purine because both comprise a nitrogenous base, that is, the molecules retain complementary structure. [Solutions]

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Adenine and Guanine within DNA and RNA.

Thymine in DNA, Uracil in RNA only, Cytosine in RNA and DNA both.

Purines have one pentose and one hexose ring.

Pyrimidines have one hexo-cyclic ring.

Chemical formula of purine – C5H4N4

Chemical formula of pyrimidine – C4H4N2

Pyrimidines are insoluble in water.

Purine catabolic end product – uric acid.

Pyrimidine catabolic end product – carbon dioxide, beta-amino acids and ammonia.

Purine has a higher melting point – 214°C

Pyrimidine has a lower melting point – 22°C

Molecular mass of purine – 120.115g/mol

Molecular mass of pyrimidine – 80.08 g/mol

Biosynthesis takes place in the liver.

Biosynthesis takes place in different tissues.