Question

Which of the following statements is true about two-dimensional electrophoresis?

• A. Separates proteins of identical molecular weight, same pI but different charge
• B. Separates proteins of different molecular weight and different pI
• C. Separates proteins of identical molecular weight that differ in pI
• D. Isoelectric focusing is also termed as two-dimensional electrophoresis

Hint:

In two-dimensional electrophoresis, isoelectric focusing separates proteins based on their pI, and SDS-PAGE separates them based on molecular weight.

Answer 1

The Correct Option is D

Two-dimensional electrophoresis runs isoelectric focusing (separation by pI) as its first dimension and SDS-PAGE (separation by molecular weight) as its second dimension.

Proteins with the same pI and molecular weight cannot be separated by this method, so that option overstates its resolving power. Saying it only separates proteins that differ in both molecular weight and pI, or only describing the pI-based separation of same-weight proteins, each capture just one piece of the full two-step design.

The statement that correctly identifies isoelectric focusing as the term closely tied to this two-dimensional method is the one that holds.

Answer 2

Looking at this from the angle of how the terminology developed and what each step contributes to the final result:

1. Separates proteins of identical molecular weight, same pI but different charge: Charge at a given pH is what pI already measures, so two proteins with an identical pI have already been defined as having matching net-charge behaviour under this method's conditions; this option describes a distinction the method's own separating parameter cannot make.
2. Separates proteins of different molecular weight and different pI: Framing the method as needing both differences simultaneously misrepresents a two-stage process where each stage independently resolves proteins differing in just one of the two properties.
3. Separates proteins of identical molecular weight that differ in pI: This isolates only the contribution of the first-dimension step and mislabels that partial contribution as the definition of the whole two-dimensional technique.
4. Isoelectric focusing is also termed as two-dimensional electrophoresis: Because isoelectric focusing gives this method its defining first-dimension character, it is commonly used interchangeably with the name of the overall technique in practice.

The first three options each mischaracterize how the two separation stages actually work, leaving the naming statement as the one that correctly reflects standard usage.

So, the correct answer is isoelectric focusing is also termed as two-dimensional electrophoresis.