tRNA placement mechanism

[SaintJude]

Which of the following observations proves that the anticodon of a tRNA molecule and not the amino acid that it carries, recognizes and binds to the mRNA code at the ribosome?

A. A trNA carrying a valine but with an isoleucine anticodon does not place any amino acid
onto a growing peptide chain when an isoleucine mRNA codon is present.

B. A tRNA carrying a valine with a valine anticodon places a valine onto a growing peptide chain
when only the first two bases of anticodon pairs with the mRNA codon.

C. A tRNA carrying a valine with a valine anticodon does not place any amino acid
onto a growing peptide chain when only the first two bases of anticodon pairs with the mRNA codon.

D. A tRNA carrying a valine but with an isoleucine anticodon places a
valine onto a growing peptide chain when an isoleucine mRNA codon is present.

How is this the answer?? (answer hidden, highlight) --> D

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[MedPR]

Is it D?

A is the opposite of what you are trying to prove.
B is saying that the anti-codon does not need to completely match up with a codon since only 2 pairs match.
C doesn't prove anything. It supports that you need 3bp recognition, which is what you would expect since codons are 3 nucleotides long.
D says that the isoleucine anticodon on tRNA recognizes the codon on mRNA and inputs whatever amino acid it is carrying. Valine, in this case.

 

[SaintJude]

Yes it's D, and I can see clearly now....thanks. I was so set on the notion that a tRNa with a isoleucin anticodon could only incorporate an isoleucin--which isn't necessarily true.

How is this possible? Why would a tRNA of an isoleucin anticodin carry a valine? Was it engineered?

 

[MT Headed]

Right, hopefully this doesn't happen much in nature!