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Genetics/Thymine and Uracil


Why does RNA use Uracil instead of Thymine? Is there any major difference between the two besides that one is in RNA and the other is in DNA? Just asking out of curiosity.

Hi Zoe,

This is a popular Q and also has several theories proposed by many biologists.
Reason for DNA not using Uracil: If DNA used uracil, the cell would have a tough time deciding whether the uracil  was generated from a mutation leading to the deamination of cytosine. That is: should it be there or not.  There is probably logical way of differentiating legitimate uracil from uracil produced by the mutation of cytosine, and so not knowing which uracil should be removed and which to be kept.  

RNA uses the “cheaper” uracil since these C to U mutations are not as harmful in RNA, and it is short-lived and synthesized in greater quantities compared to DNA. So not much expenditure.
uracil was recognized better by the primitive RNA pol
RNA polymerase preferred uracil so as not to compete with DNA polymerases for thymine in primitive cells.



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Thanemozhi Natarajan


Answers in Genetics, genomics, cytogenetics of syndromes, congenital anomalies, cancer, clinical genomics and interpretation of omics data.


More than 10 years. Doctoral research thesis on Congenital anomalies and cytogenetics, Recurrent reproductive failure and chromosomal abnormalities. Postdoctoral experience in Breast cancer research. Current: Clinical Genomics and Pharmacogenomics.


Cancer Cell International, Cancer Epidemiology Biomarkers and Prevention, Breast cancer research and treatment, Indian Journal of Pediatrics, BMC Proceedings, Pharmacogenetics and Genomics, Human Molecular Genetics, Frontiers in Genetics, Cancer Biomarkers.

PhD Biomedical Genetics

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University Grants Commission Award for pursuing PhD level research (India); Travel awards to attend conferences.

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Post doctoral experience Cancer research, molecular epidemiology Current: Clininical Genomics and Pharmacogenomics

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