Aamc 11 bs #138

[justhanging]

QQ:

The precursor of EGP (protein) is translated from a transcript that has had one nontemplated nuclotide added to the open reading frame. This change doesn't add or eliminate a stop codon. Compared with the preotein sGP, which is produced from the unedited transcript, EGP most likely has the same primary:

A) Amino- terminal sequence as sGP, but different primary carboxy- terminal sequence.

B) Carboxy- terminal sequence as sGP, but different primary amino- terminal sequence.

I don't really understand this question, or what they mean by "adding one nontemplated nucleotide to the open reading frame". I do understand that is a posttranscriptional modification of mRNA where one nucleotide is added. But where is it added? Can some clarify.

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[MT Headed]

QQ:

The precursor of EGP (protein) is translated from a transcript that has had one nontemplated nuclotide added to the open reading frame. This change doesn't add or eliminate a stop codon. Compared with the preotein sGP, which is produced from the unedited transcript, EGP most likely has the same primary:

A) Amino- terminal sequence as sGP, but different primary carboxy- terminal sequence.

B) Carboxy- terminal sequence as sGP, but different primary amino- terminal sequence.

I don't really understand this question, or what they mean by "adding one nontemplated nucleotide to the open reading frame". I do understand that is a posttranscriptional modification of mRNA where one nucleotide is added. But where is it added? Can some clarify.

It was added somewhere in the middle. Since this is a frameshift, everything downwind of the addition will most likely be different.

The question is basically asking, if you change everything from the middle to the end of an amino acid sequence, which end changes and which end would remain the same?

It basically asks, when amino acids are assembled into proteins, are they built from the amino to the acid direction, or the acid to the amino direction?

The answer is that amino acid sequences are always assembled N to C, much like nucleotide sequences are built 5 to 3.

 

[dancerdoc89]

I had the exact same question about this one...I had assumed the new nucleotide was slapped on the 5' end of the RNA (not within the ORF) since the question clarified that the "change does not create or eliminate a stop codon"...I took this as meaning, "if it's not added to the 3' end, it must be added to the 5' end!"

Then again, had this change been added to the 5' end of the RNA, or the beginning, the entire AA sequence (amino and carboxy-terminal) would be different, which is not an answer option whatsoever.

Anyway, this was helpful!

 

[muhali3]

I accidentally read codon instead of nucleotide for some reason, leading me to pick C.

 

[Dr Weird]

If you add just one nucleotide, it will have to cause a frameshift and remove a stop codon, right?

Stop Codons:
UAG
UAA
UGA

They all start with U, so if you add one nucleotide before any of those (example, guanine), to make say:
GUA(Gxx)
GUA(Axx)
GUG(Axx)

where the "xx" are the next two nucleotides 3' in the RNA sequence, there is no way the parenthetical next codon in the new reading frame will be a stop codon, because none of the three possible stop codons ends in U.

So don't both A and B contradict the statement that no stop codons were created or deleted? I'm sure I'm just missing something (probably don't need to know stop codons for this, I'm guessing - had to lok them up myself)

 

[MedPR]

If you add just one nucleotide, it will have to cause a frameshift and remove a stop codon, right?

Stop Codons:
UAG
UAA
UGA

They all start with U, so if you add one nucleotide before any of those (example, guanine), to make say:
GUA(Gxx)
GUA(Axx)
GUG(Axx)

where the "xx" are the next two nucleotides 3' in the RNA sequence, there is no way the parenthetical next codon in the new reading frame will be a stop codon, because none of the three possible stop codons ends in U.

So don't both A and B contradict the statement that no stop codons were created or deleted? I'm sure I'm just missing something (probably don't need to know stop codons for this, I'm guessing - had to lok them up myself)

This thread is 9 months old.

 

[GeorgiadisMD]

This thread is 9 months old.

And he has a legitimate question... your point?

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