Date: August 2007
Why does RNA has uracil instead of thymine?
The difference between thymine and uracil is a single methyl
group in thymine that does not appear in uracil, in fact, the
chemical name of thymine is 5-methyl uracil. This methyl group
is located in a region of thymine that is not involved in Hydrogen
bonding to adenine so it behaves just like uracil. The reason why
DNA and RNA are different, only God knows!
Ron Baker, Ph.D.
The backbone of RNA is a ribose sugar rather than a deoxyribose
sugar that identifies DNA. "Deoxy" refers to the fact that it is
a ribose sugar missing an oxygen atom. It has been shown that
thymine will not bond correctly with the ribose sugar backbone
configuration. Uracil will and acts as a functional substitute.
Guanine, cytosine and adenine will bond with either.
Since you have failed to identify your age. You will have to be
happy with this explanation.
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Update: June 2012