What would happen if valyl tRNA synthetase (val-rs) couldn't distinguish between valine and isoleucine?

Answer 1

At positions where valine is normally placed you would have either valine or isoleucine (you said that it would be impossible for the enzyme to distinguish between the two, thus it could incorporate any of the two in the amino acid-tRNA complex).

Assuming an identical affinity for the two substrates the ratio of Valine/isoleucine incorporation would depend on the concentrations of the free amino acids. This in turn would depend on the environment (nutrients), metabolic status, the percent of isoleucine in the normal isoleucine-tRNA complexes,etc.

Anyway, redargless of the exact ratio, you would have some incorporation of isoleucine residues in the place of valine. Both are hydrophobic and you would expect to find them (with a higher frequency) in the hydrophobic core of proteins.Though their structrure is similar, isoleucine is more bulky. Thus we would expect isoleucine to disrupt the normal packing of the hydrophobic residues in the core. This would change the structure of the protein making it less functional or completely inactive, or unstable, etc.

The effect would be on many proteins, so probably such a phenomenon would be lethal for the cell.

Answer 2

You would have isoleucine incorporated into proteins in positions where valine should be. There would be a lot of problems.

Answer 3

Your proteins in your body would be structurally different and probably wouldn't function as they are supposed to. If I had to guess, I don't think you could live.