Q ID: 2032 Uworld tRNA question

[ih8mcat]

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Maybe someone can help me out with this. According to pg 74 of 2011 FA...if aminoacyl-tRNA makes a mistake charging an AA on a tRNA - it hydrolyzes the bond.

According to this Uworld question about an inaccurate leucine charged in place of a proline - the incorrect aa is incorporated. Any ideas? I'm leaning towards more of what FA says - because wiki says something similar.

 

[AlexMorph]

The Uworld question is saying that the tRNA failed to hydrolyze the bond. It incorporated the wrong amino acid on accident. Basically, it's asking, will the ribosome recognize that the tRNA brought in the wrong amino acid, the answer to which is no. The ribosome will trust the tRNA did its job properly.

 

[da8s0859q]

The Uworld question is saying that the tRNA failed to hydrolyze the bond. It incorporated the wrong amino acid on accident. Basically, it's asking, will the ribosome recognize that the tRNA brought in the wrong amino acid, the answer to which is no. The ribosome will trust the tRNA did its job properly.

👍

I remember that question and had the same thought at first when I read that in FA. UW's just asking, "So hey, if the charged tRNA ****ed up and is carrying an AA it isn't supposed to carry based on its anticodon structure at the other end of the AA on the 3' head, is there anything to keep it from inserting the AA onto the growing peptide chain?"

 

[ih8mcat]

thanks guys, some of these biochem question are crazy, i guess i just over thought it, 15 more to go!

 

[abmd]

I have kind of a related question. there are a few UW world questions with PKAs of amino acids. Do we need to know these?

 

[ArcGurren]

I have kind of a related question. there are a few UW world questions with PKAs of amino acids. Do we need to know these?

I'm going to take the hit on the one question where I get asked this or just approximate based on which ones are acidic vs basic 🙄 I hated those questions, I never bothered to remember the structures of any of them except glycine and valine following the MCAT

 

[EvryBreathAGft]

i'm still stuck on that tRNA question. wouldn't the anticodon on the tRNA (with leucine) not match the codon intended to match proline? how would the wrong tRNA still be able to bind??

 

[da8s0859q]

i'm still stuck on that tRNA question. wouldn't the anticodon on the tRNA (with leucine) not match the codon intended to match proline? how would the wrong tRNA still be able to bind??

The anticodon is the anticodon is the anticodon. The tRNA is supposed to bind the right AA, but there's no proofing beyond that. So if it doesn't, the anticodon is still gonna say "hey, 'sup?" to its codon, and stick that AA in the forming peptide.

I've not heard of an AA binding and inducing conformational change to shift the frame, if that's what you're getting at.

 

[EvryBreathAGft]

so the anticodon is still the same sequence? let's say the mRNA is CCU, the tRNA will still be GGA, even though it's not carrying proline?

 

[ih8mcat]

i'm still stuck on that tRNA question. wouldn't the anticodon on the tRNA (with leucine) not match the codon intended to match proline? how would the wrong tRNA still be able to bind??

So i google searched aa trna synthetase mischarging and the very first google books link has the answer...i would copy paste...but u world wont let me do that

so enzyme that carries aa - trna binding DOES have proofreading ability as first aid suggests...but that's because this isn't a simple process...we're not just slapping on an aa onto the trna - it requires some sort of hydrolysis step - and this is where the proofreading comes into play...and according to this link it lowers the rate of misplacement

but once it's on there - it's on there...like the above poster said - so no take backs at that point

hope that helps!

 

[da8s0859q]

so the anticodon is still the same sequence? let's say the mRNA is CCU, the tRNA will still be GGA, even though it's not carrying proline?

As far as I know, yes.