This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Structure and function of protein, Subject name: Biochemistry
Electrophoresis done under pH gradient is 
Select and explain. 
A. Isoosmotic, B. Isoelectric, C. Ion exchange, D. None
B: Isoelectric
Answer: B: Isoelectric 
Explanation: Ionic buffers called ampholytes and an applied electric field is used to generate a pH gradient within a polyacrylamide matrix. Applied proteins migrate until they reach the region of the matrix where the pH matches their isoelectric point (pI), the pH at which a peptide&;s net charge is zero. IEF is used in conjunction with SDS- PAGE for two-dimensional electrophoresis, which separates polypeptides based on pI in one dimension and based on Mr in the second (Figure 45). Two-dimensional electrophoresis is paicularly well suited for separating the components of complex mixtures of proteins.Ref: Harper&;s Illustrated Biochemistry a LANGE medical book twenty-sixth edition Page no: 24