Practice question

Isoelectric point defines pH at which a protein carries zero net charge because numbers of protonated basic residues and deprotonated acidic residues are balanced. When buffer pH equals pI, electrostatic attraction toward anode or cathode ceases, resulting in no net electrophoretic migration and stationary focusing. At pH 7, a protein that shows no movement must possess balanced charges at that pH, indicating its isoelectric point is approximately 7. Proteins with pI values of 5, 6 or 8 would carry net negative or positive charge at pH 7 and would migrate toward anode or cathode respectively under electric field.