Help with protein synthesis problem

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rdpioneer
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Help with protein synthesis problem

Post by rdpioneer » Sat Feb 02, 2008 12:41 am

Hello,
I did an exam about protein synthesis and I found a question that I couldn't answer.
I want to know how to answer it because i want to study biology.

The problem is this:
If we have the sequence of nitrogene bases of a segment of DNA:
3' TAC GGA TTC AGA 5'

the sequence of anticodons of RNAr and corresponding to the RNAt originated from this segment is:

the answer:
AUG CCU AAG UCU

So, I don't get it because that answer seems to me that is the RNAm and not the RNAt.
I think it must be
UAC GGA UUC AGA

by the way, why they mention RNAr??

thank you very much

blcr11
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Re: Help with protein synthesis problem

Post by blcr11 » Sat Feb 02, 2008 12:56 pm

Something's not quite right with what you've written. And I've no idea why rRNA would have been mentioned other than to say that the actual peptide synthesis goes on on the ribosomes, but you can't say anything about rRNA sequence from what you've been given.

Assuming that your labelling is correct and that you were given the (+) strand of the gene, the DNA sequence was given 3'->5', which is the reverse order with respect to the N-term->C-term direction of the protein. If you re-write the DNA sequence in 5'->3' order,then the mRNA should have the same polarity with U's everywhere there were T's in the original sequence. Then the anti-codon loops will have the complement of each codon. Strictly speaking there is no "sequence" of anti-condons in the sense of the mRNA molecule. Each three-base complement is on a separate tRNA molecule, they not strung along together in a single sequence of "anti-codon" RNA. So, when you do that, you get the given answer. There are other ways to interpret the DNA sequence that was given, but this way comes up with the "correct" answer you were given.

DNA – 5’-TAC GGA TTC AGA-3’

mRNA – 5'-UAC GGA UUC AGA-3'

anti’s – 3’-AUG CCU AAG UCU-5’

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