In: Biology
11. Why do you think thymine is used in DNA and uracil used in RNA when the other three bases are the same in each?
Ans- Thymine is methylated uracil which increases the stability of the base. One reason for use of thymine in DNA is to protect it. Methylation of base protects the DNA from nuclease by making it unrecognisable. Since RNA is shorter lived than DNA , it gets up by relatively cheaper uracil. If uracil was present in DNA, it would be difficult for cell to decide whether uracil generated from mutation- the deamination of cytosine- should be there in not. If uracil was used instead of thymine, cell would have no way to distinguish uracil and uracil produced by mutation of cytosine. By using thymine in DNA, this issue is resolved . However RNA uses cheaper uracil because these mutations are not harmful in RNA as it is synthesized in large quantities and is short lived. Also finally, addition of hydrophobic methyl group changes the shape of DNA and allows thymine to base pair with adenine whereas uracil would pair less selectively.