Electrophoresis basics — In native PAGE, proteins are separated primarily on the basis of what properties?

Introduction:
Electrophoresis separates biomolecules by their movement in an electric field through a gel matrix. This question focuses on native PAGE, where proteins retain their folded state and intrinsic charges, in contrast to denaturing SDS PAGE.

Given Data / Assumptions:

• Native PAGE preserves protein conformation and complexes.
• No uniform charge to mass ratio is imposed by detergents.
• Gel matrix introduces size dependent friction.

Concept / Approach:
In native PAGE, mobility reflects a balance between electrical force and frictional drag: v ∝ (q * E) / f, where q is net charge and f depends on size and shape. Larger complexes experience greater friction and move more slowly; proteins with greater net charge in the running buffer move faster toward the opposite electrode.

Step-by-Step Solution:

Verification / Alternative check:
Comparing a protein and a larger complex with the same charge shows slower migration of the larger species. Changing buffer pH alters net charge and shifts mobility, confirming the role of q and size together.

Why Other Options Are Wrong:

• Net negative charge or net positive charge alone: sign by itself does not define mobility or separation without magnitude and size.
• Net positive charge and size: restricts sign unnecessarily; proteins can be negative or positive depending on pH.
• Isoelectric point only: relevant for isoelectric focusing, not native PAGE in a constant pH gradient.

Common Pitfalls:
Confusing native PAGE with SDS PAGE. In SDS PAGE, size dominates due to near constant charge to mass ratio; in native PAGE, both charge and size (and shape) matter significantly.

Final Answer:
net charge and size.