AAMC Sample BB #19

[deleted647690]

When I did this question, I went with Lysine because they mentioned that the modified nucleotide, when run over a column that binds Lysine, did not elute. Therefore, it was Lysine.

I definitely misunderstood what Lysine has to do with this nucleotide. So this modified structure was located downstream of Lysine? Why did it not elute when run over a Lysine specific column?

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[663697]

I think it says it binds lysine tRNA rather than the amino acid itself, I may be wrong though. In any case I think you just have to look at the structure of the modified nucleotide and you will notice at the top there is the R group of threonine which projects off of the alpha carbon adjacent to the N and C terminals of the amino acid.

 

[aldol16]

The modified structure is located immediately 3' of the lysine tRNA. In other words, as translation is occurring, the CDKAL1 enzyme will spot the tRNA that has bound immediately 3' to the lysine tRNA and it'll modify it to make the structure shown. The point of running it over a column that binds lysine tRNA is that if the enzyme specifically alters only what is next to the lysine tRNA, then all of the alterations, since they will be right next to the lysine tRNA, will bind to the column and you shouldn't detect any modified tRNAs in the elutant. But if the enzyme is not specific to what is next to only lysine tRNA, then you'll see modifications in the elutant, where there is no lysine tRNA.