mechanism to make a 250 aa protein from a 300 bp ORF

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MrMistery
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mechanism to make a 250 aa protein from a 300 bp ORF

Post by MrMistery » Wed Nov 11, 2009 1:00 am

this semester i am tutoring a class on introductory molecular biology and one of the questions on the problem set which I am bound to get questions on is this:
"You find a bacterial gene with a 300bp putative ORF, but surprisingly the product after translation is 250aa.
You sequence the peptide and determine that residue 101 is amino acid X, a previously
undescribed amino acid."
How the hell can you explain this? The amino acid X part i am guessing has nothing to do with it. they ask about it in another part of the question, and i'm guessing the answer they want is something along the lines of "it's the same thing as selenocysteine only with telurium". My question concerns the extra amino acids - for a 300 bp ORF one would expect a 99 or 98 aa peptide. where do the other amino acids come from? I don't know of any mechanism that can account for that, but obviously there must be one if they ask about it in this class.
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mith
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Post by mith » Wed Nov 11, 2009 2:07 am

"putative"
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Post by canalon » Wed Nov 11, 2009 2:16 am

I think it would be similar to the selenocysteine story, coded by a stop codon:
http://en.wikipedia.org/wiki/Selenocysteine
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Post by MrMistery » Wed Nov 11, 2009 2:17 am

yeah, actually i figured that out as a student was asking me :-)
That's what they wanted for sure.
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Post by JackBean » Wed Nov 11, 2009 9:12 am

cool, here can one find many interesting questions :)
I will have to ask some teacher about that, whether they will be able to figure out :lol:
http://www.biolib.cz/en/main/

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Post by MrMistery » Wed Nov 11, 2009 12:02 pm

it's a pretty easy question if you first think about the abnormal amino acid and then about the length. but you have to look at it from the right perspective. Nevertheless, a pretty fun one indeed
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Re: mechanism to make a 250 aa protein from a 300 bp ORF

Post by zami'87. » Thu Nov 12, 2009 8:17 am

nice one :) Luckily they mentioned amino acid X..In science right questions are more important than answers.
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Re: mechanism to make a 250 aa protein from a 300 bp ORF

Post by mcb52teachingstaff » Thu Nov 12, 2009 9:14 pm

Image

edit: The misunderstanding has been resolved;I am removing the text but leaving the finger-wagging Rich.
Last edited by mcb52teachingstaff on Fri Nov 13, 2009 1:56 pm, edited 1 time in total.

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MrMistery
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Post by MrMistery » Fri Nov 13, 2009 1:19 am

no I have not. please see my private message.
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Post by mith » Fri Nov 13, 2009 2:23 am

lol, seriously?
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Post by JackBean » Fri Nov 13, 2009 4:26 am

what? :roll:
http://www.biolib.cz/en/main/

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MrMistery
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Post by MrMistery » Fri Nov 13, 2009 6:26 am

What happened was that one of the teachers of the course discovered that I asked the question over the internet, which is obviously not allowed and is considered cheating. Of course, i was not cheating because I am not taking that course, I am tutoring for it (which i said, but obviously there was no reason for them to believe me). The problem was that actual students in the class could have found this page and gotten the answer, which is obviously not good (and completely my fault).

Anyway, i straightened it out and edited the posts so the name of the made-up amino acid will not come up on a google search (generally we don't do that here, but this is an exception).

Just goes to show you: don't post homework questions on biology-online.org

PS: I am considering making this a sticky

PS2: The person in the GIF is Richard Losick, the professor teaching the class. a great scientist and a great man
"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter

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