Answer
The two codons for Glu are GAG and GAA.
The four codons for Val are GTT, GTC, GTA and GTG.
A GAA to GTA base change can account for the Glu to Val point mutation in sickle-cell afflicted hemoglobin.
Work Step by Step
Number of ATPs necessary for synthesizing a polypeptide with n residues is 4n-1.