In sitedirected mutagenesis experiments Gly is often success

In site-directed mutagenesis experiments, Gly is often successfully substituted for Val, but Val can rarely substitute for Gly. Explain.

Solution

Val can rarely substitute for Gly.

Explanation:

A Gly amino acid side chain is just a H atom but valine has a large side chain with many C and H atoms. Since Gly has a small side chain it has the most flexibility out of all the amino acids, this means that the peptide backbone can adopt unique bond angles that it cannot achieve with any other amino acid. This is why the gly amino acid cannot be successfully replaced by a Val.

Gly is often successfully substituted for Val.

Explanation:
The gly can replace the val since the gly will most likely not fully disrupt the interactions around where the val side chain was or change the peptide chain characteristics so dramatically.