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Old 06-23-2011
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DNA UW Question: Which kind of mutation?

A non-functional protein expressed in a cell culture contains 156 AA residues rather than the 130 AA residues normally seen in the functional protein. The non-functional protein is still detected by specific antibodies against the functional protein. Which of the following point mutations best explains the observed finding?

A. Silent mutation in intron 2.
B. Missense mutation in exon1.
C. Frameshift mutation in codon 3 of exon1
D. Non-sense mutation in exon2
E. Splice site mutation.

Please explain the answer choices as this concept is really confusing me
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Old 06-23-2011
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Splice site??? The way I see it there are A LOT of extra AA so they must have have a problem with the splicing...
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Old 06-23-2011
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The way i see it, is Framshift mutation is the change from a NORMAL protein in this case 156 AA to a non-functional protein 130AA..

Answer is C. <-

Last edited by rulz; 06-23-2011 at 06:51 AM.
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Quote:
Originally Posted by struggle View Post
A non-functional protein expressed in a cell culture contains 156 AA residues rather than the 130 AA residues normally seen in the functional protein.The non-functional protein is still detected by specific antibodies against the functional protein.Which of the following point mutations best explains the observed finding?
A.Silent mutation in intron 2.
B.Missense mutation in exon1.
C.Frameshift mutation in codon 3 of exon1
D.Non-sense mutation in exon2
E.Splice site mutation.

Please explain the answer choices as this concept is really confusing me
Since the non-functional protein is still detected by specific antibodies against the functional protein, the problem is not in the exons...
So, we have A or E
In A...Silent mutation = wrong, clearly one is 156AA and the other 130AA (so, not "silent")

So, the correct answer should be E
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Old 06-23-2011
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Quote:
Originally Posted by rulz View Post
The way i see it, is Framshift mutation is the change from a NORMAL protein in this case 156 AA to a non-functional protein 130AA..

Answer is C. <-
but the normal protein has 130AA...and the non-functional 156AA
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Old 06-23-2011
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Answer should be E. Splice site mutation.

The question stem says that antibodies are able to recognize specific parts of the protein still which means that much of the proteins secondary structure is still conserved. This must mean that much of the primary structure (order of amino acids) is fairly conserved. It also says that the protein is longer by X amount of amino acids.
Introns are flanked by GU and AG sequences. SO they look like this:

Exon GU Intron AG Exon GU Intron AG etc....

So if there is a mutation in the splice sites (GU or AG), then splicing may not occur correctly. If a mutation occurs in an AG site, then the splicesome will pick the first GU and go to the NEXT AG which would mean it would splice out an extra exon which was supposed to be a part of the original mRNA. IF the mutation was at a GU site, then you can see that it'll skip that GU and go to the next GU sequence and will therefore leave an intron in the mRNA sequence. This will thus create a longer protein with most of the sequence still conserved. THUS conserving its ability to be recognized by the mentioned Antibodies. There are many possibilities and combinations in splicing so the above two are not the only possibilities. But the only answer choice that produces such a protein with characteristics mentioned in the question would be E.
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Quote:
Originally Posted by bebix View Post
but the normal protein has 130AA...and the non-functional 156AA
Hahah, my bad i read the question wrong! =)
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Old 06-23-2011
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Yes the answer is E..
The introns are non-expressed part and is removed as a part of post transcriptional modification.
If the introns are not removed large proteins with altered function but preserved immunoreactivity are produced.
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