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Author Topic: Why does RNA use uracil as a base instead of DNA's thymine?  (Read 17648 times)

Offline Chemistry4me

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Seeing as this board has been quite quiet lately, and also to help out our dear friend, I have this udder :-\ question:

Anyway, here it is, are you ready?

Why does RNA use uracil as a base compared to DNA's thymine? I know one is more stable than the other, but apart from that, is there any reason for the difference in the bases?
« Last Edit: 26/05/2009 07:03:41 by Chemistry4me »


 

Offline Chemistry4me

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Why does RNA use uracil as a base instead of DNA's thymine?
« Reply #1 on: 27/05/2009 05:46:54 »
Anyone have an idea?
 

Offline Variola

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Why does RNA use uracil as a base instead of DNA's thymine?
« Reply #2 on: 28/05/2009 23:03:57 »
Anyone have an idea?

I do, but I stress it is an educated guess!!!) Hey that rhymes!!

I think there maybe several reasons, but one of which are intrinsic terminators ( Rho independant). These terminators only need themselves to work,they consist of a short inverpted repeat ( about 20 NT) followed by a stretch of AT base pairs. (about 8 NT) They don't affect the RNA polymerase until they have been transcribed, i.e they function in the RNA rather than the DNA. When the polymerase transcribes the inverted repeat sequence the RNA that is made can double back on itself to form a loop, called a hairpin.This acts as a terminator by disrupting the elongation.
But it only really works when followed by the length of the (now) AU base pairing, This is because at the time the RNA is forming, it is only held on the the template by AU pairs. As these are much weaker than even AT pairs, they are more easily disrputed by the effects of the stem loop on the transcribing polymerase and the RNA will more readily disassociate.
 

Offline Chemistry4me

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Why does RNA use uracil as a base instead of DNA's thymine?
« Reply #3 on: 29/05/2009 04:41:18 »
Thank you my dear. :)

I'd forgotten that they were so similiar:



After a bit of searching and rummaging, I found this explanation:

Quote
The answer is: methylation protects the DNA. Beside using dT instead of dU, most organisms also use various enzymes to modify DNA after it has been synthesized. Two such enzymes, dam and dcm methylate adenines and cytosines, respectively, along the entire DNA strand. This methylation makes the DNA unrecognizable to many Nucleases (enzymes which break down DNA and RNA), so that it cannot be easily attacked by invaders, like viruses or certain bacteria. Obviously, methylating the nucleotides before they are incorporated ensures that the entire strand of DNA is protected. Thymine also protects the DNA in another way. If you look at the components of nucleic acids, phosphates, sugars, and bases, you see that they are all very hydrophilic (water soluble). Obviously, adding a hydrophobic (water insoluble) methyl group to part of the DNA is going to change the characteristics of the molecule. The major effect is that the methyl group will be repelled by the rest of the DNA, moving it to a fixed position in the major groove of the helix. This solves an important problem with uracil - though it prefers adenine, uracil can base-pair with almost any other base, including itself, depending on how it situates itself in the helix. By tacking it down to a single conformation, the methyl group restricts uracil (thymine) to pairing only with adenine. This greatly improves the efficiency of DNA replication, by reducing the rate of mismatches, and thus mutations.

http://www.madsci.org/posts/archives/1997-12/879354206.Bc.r.html
 

Offline Variola

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Why does RNA use uracil as a base instead of DNA's thymine?
« Reply #4 on: 29/05/2009 08:37:06 »
Nice find C4M! :)

I think there are other reasons/theories too, but without rifling through my lecture notes I can't be certain of them. Poly-U tails are important with something I seem to recall...<hazy memory icon>


Ugh! did you have to put the structure of them up?? You know I am phobic with anything to do with the C word... *shudder*
 :)
 

Offline Chemistry4me

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Why does RNA use uracil as a base instead of DNA's thymine?
« Reply #5 on: 29/05/2009 08:49:09 »
I'm a C word! :D Or perhaps you're talking about Cummings? ;)
 

Offline Variola

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Why does RNA use uracil as a base instead of DNA's thymine?
« Reply #6 on: 29/05/2009 08:52:51 »
I'm a C word! :D Or perhaps you're talking about Cummings? ;)

I know.... I only tolerate your use of the C word as I like you. ;)
My adventure into the C word forum the other day took nerves of steel! lol
« Last Edit: 29/05/2009 08:56:20 by Variola »
 

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Why does RNA use uracil as a base instead of DNA's thymine?
« Reply #6 on: 29/05/2009 08:52:51 »

 

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