Question

Explain how enzymes are able to differentiate between two molecules that have similar shapes and chemical groups like valine and threonine.

Answer 1

It is excluded from this active site and hence doesnot become adenylated and transferred to through - tRNA. The zinc site is less well suited to discrimination against series because this amino acid doesnot have a hydroxyl group that can bind to the zinc Threonine is particularly similar to two other amino acids namely valine. Valine has almost exactly the same shape as threonine, except that it has a methyl group in place of a hydroxyl group The structure of the amino - acid binding site of threonyl - tRNA syn theta se reveals how valine is avoided. The enzyme contains a zinc ion, bound to the enzyme by two histidine residues and one cysteine residue. Like carbonic anhydrase, the remaining coordination sites are available for substrate binding. Threonine coordinates to the zinc ion through its amino group and its side - chain hydroxys group. The side chain hydroxys group is further recognized by an aspartate residue that hydrogen bonds to it.