Talk about gene mutations causing molecular diseases.

Alteration of protein that doesn't have enzymatic activity (sickle cell anemia, HbA (normal) has 4 subunits, attached to hemes with one iron atom, HbS (sickled) decreases RBC life and changes it into sickle shaped, beta subunit is the affected one, substitution of GTG into GAG in number 6 aa of beta.)