Differences Between Purines and Pyrimidines

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 

1. Purine 

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. 

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2. Pyrimidine 

Pyrimidine is heterocyclic in nature with the aromatic compound only consisting of one carbon ring and two nitrogen atoms. 

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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) –

  • Adenine 

  • Guanine 

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Pyrimidines consist of the remaining bases in DNA and RNA –

  • Uracil 

  • Cytosine 

  • Thymine 

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Function of Purine and Pyrimidine Bases 

1. Purine Catabolism 

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. 

2. Pyrimidine Catabolism 

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 -

Purine vs Pyrimidine 

Parameters

Purines

Pyrimidines

Source 

Adenine and Guanine within DNA and RNA.

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

Size 

Purines are bigger in size. 

Pyrimidines are smaller in size.

Structure 

Purines have one pentose and one hexose ring. 

Pyrimidines have one hexo-cyclic ring. 

Chemical formula 

Chemical formula of purine – C5H4N4

Chemical formula of pyrimidine – C4H4N2

Solubility 

Purines are soluble in water.

Pyrimidines are insoluble in water.

Catabolic end product 

Purine catabolic end product – uric acid. 

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

Melting point 

Purine has a higher melting point - 214°C

Pyrimidine has a lower melting point - 22°C

Molecular mass 

Molecular mass of purine – 120.115g/mol

Molecular mass of pyrimidine – 80.08 g/mol

Location of biosynthesis 

Biosynthesis takes place in the liver. 

Biosynthesis takes place in different tissues. 


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 

i. Which of the Following are Nucleotides?

(a) Nitrogen bases + Pentose sugar + Phosphate 

(b) Nitrogen bases + Pentose sugar

(c) Purine bases 

(d) None of the above

ii. _________________ is a Purine Base. 

(a) Uracil 

(b) Thymine 

(c) Cytosine 

(d) Adenosine

[To check your answer, see the solution mentioned at the end of the article]

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FAQ (Frequently Asked Questions)

1. What is the Function of Purines and Pyrimidines?

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. 

2. What is the Major Difference Between Purines and Pyrimidines?

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

3. Why do Pyrimidines Bond with Purines?

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

[Solutions]

i. (a) Nitrogen bases + Pentose sugar + Phosphate 

ii. (d) Adenosine