Hi all, im new...

 

I'm Fuad and i come from Bosnia. I study biology.

 

Also, my english is bad, so please bear with me.

 

 

 

 

Ok, about my question. Well, they always teach you that RNA has Uracil base, and that DNA has Thymine instead. But I never learned why! Why did DNA molecule evolved that way... why didn't it keep Uracil, why replace it with Thymine?

Thymine is more stable than Uracil

Another (and arguably the more important) reason is fidelity.

Just as background: thymine formed by methylation of uracil. But it is also possible to get uracil by deamination of cytosin. So if U is used in DNA and a C converts to U, there is no way to detect this point mutation (as it would not be possible to distinguish between an legitimate and an illegetimate uracil) and repair it.

In addition, U is more promiscuous in its bonding with other base pairs as compared to thymine. This is because the additional (hydrophobic) methyl group in thymine inhibits confirmation changes and thus greatly reduces the ability of thymine to interact with other bases as compared to uracil.

Edited February 23, 200916 yr by CharonY

Mokele's answer is the best (and it's simple and to the point, LOL), and if you want you should go to http://en.wikipedia.org/wiki/Uracil, and then you will see a passage called "Properties", and read that passage, it will explain everything, (in depth).