SDS–PAGE characteristics — Identify the set of statements that correctly describe protein behavior in SDS–PAGE

Introduction:
This question checks recognition of three hallmark features of SDS–PAGE: denaturation, charge normalization, and size-dependent mobility. Understanding these together explains why SDS–PAGE estimates apparent molecular masses reliably.

Given Data / Assumptions:

• SDS is an anionic detergent that unfolds proteins.
• SDS binding is roughly proportional to length, producing near-constant charge-to-mass ratios.
• Polyacrylamide gels sieve molecules by size under an electric field.

Concept / Approach:
Combine the chemical action of SDS with the physical sieving of the gel. Denatured chains with similar charge density migrate according to length, so smaller chains move faster and farther during a set run time.

Step-by-Step Solution:

Verification / Alternative check:
Standard marker ladders yield linear relationships between distance migrated and log(MW), empirically validating the trio of statements.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming reducing agents are always required; some analyses run non-reducing SDS–PAGE when disulfide status is of interest.

Final Answer:
All of the above.