Differences Between Purines and Pyrimidines in DNA and RNA

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 rings 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 differences. 

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. The formation of uric acid takes place in the liver and is subsequently discharged with urine through the kidney.

In the human body, monosodium salt and un-dissociated uric acid are the least soluble. Such nature usually does not cause any problem in the human body unless urine has a very high acidic content. The 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.

Purine vs Pyrimidine 

The Differences between Purine and Pyrimidine are the following -

Bonding between Purines and Pyrimidines

Purines pyrimidines are two distinct nitrogenous nucleotide bases. They form the five nucleobases presenting DNA and RNA. Pyrimidine bases are basically heterocyclic compounds that consist of a single carbon ring having two nitrogen atoms and purine bases consist of two carbon things with a greater number of nitrogen atoms. Purines always bond with pyrimidines via hydrogen bond and each bond follows Watson Crick base-pairing rules.

Presence in DNA and RNA

Purines and pyrimidines are heterocyclic aromatic compounds having two and three molecules respectively. They serve as a major component in the production of DNA and RNA. Also, they are useful for the energy production of cells. 

In DNA: 

DNA is a material that carries information about how any living being will look and function. The major backbone of the production of DNA is the presence of purines and pyrimidines. Purine has two types: adenine and guanine. Pyrimidines have three cytosine uracil and thymine. But In DNA only four types of nitrogen bases are used which are adenine, guanine, cytosine and thymine. Adenine pairs with thymine via two hydrogen bonds whereas guanine pairs with cytosine via 3 hydrogen bonds. 

In RNA: 

RNA is an important molecule found in the blood cells and it is necessary for living beings. The major backbone of the production of RNA is purines and pyrimidines. Purine has two types and pyrimidine has three types of molecules. But in RNA only four types of molecules are present. RNA is produced with nitrogen bases as adenine, guanine, cytosine and uracil. The difference between them is that they contain sugar fibres whereas DNA contains the different sugar deoxyribose.

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 

1. 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

2. _____ is a purine base. 

(a) Uracil 

(b) Thymine 

(c) Cytosine 

(d) Adenosine

Solutions:

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

2.(d) Adenosine

Did You Know?

The identification of pyrimidine compounds took a long time. Even though its isolation took place somewhere between 1837 and 1864, the recognition of its structures did not come through till 1868.

Quick Summary 

• Purines and pyrimidines are bases introduction of DNA and RNA. 

• Purine and pyrimidine have families of Nitrogen bases that make up nucleic acids.

• Purine has two rings and pyrimidines have one ring. 

• DNA consists of purines adenine and guanine and pyrimidines cytosine and thymine. 

• RNA consists of curing adenine and guanine and pyrimidines cytosine and uracil. 

• Adenine pairs with thymine by two hydrogen bonds. 

• Guanine pairs with cytosine via three hydrogen bonds. 

• Purines are bigger and pyrimidines are smaller. 

• Purine has four nitrogen atoms and pyrimidines have two nitrogen atoms. 

• The major difference between purines and pyrimidines is their structure. 

• Bonding between them happens due to the difference in their size structure.