Practice question

Two-dimensional electrophoresis couples orthogonal separation principles to resolve highly complex proteomes containing thousands of polypeptides. First dimension is isoelectric focusing in immobilized pH gradient strips or carrier ampholyte tubes where proteins migrate under electric field until net charge becomes zero at their isoelectric point, effectively focusing at pI independent of size. This separates isoforms differing by charged modifications. Second dimension is SDS-PAGE where focused proteins are further separated by molecular mass. Charge alone or solubility does not define focusing position; isoelectric point focusing is the discriminating parameter for first dimension.