Proteins are separated by size using techniques that exploit molecular weight differences, and the correct answer is A and C only—isoelectric focusing and ion exchange chromatography do not rely on size.

Option Analysis

Each technique separates proteins differently; only some target size (molecular weight).

• A. Isoelectric focusing: Separates by isoelectric point (pI), where net charge is zero, not size. Proteins migrate in a pH gradient until they stop moving.

• B. SDS-PAGE: Denatures proteins with SDS for uniform charge, then separates by size via electrophoresis through a gel matrix—smaller proteins move faster.

• C. Ion exchange chromatography: Separates by net surface charge interactions with a charged resin, independent of size.

• D. Molecular exclusion chromatography (size-exclusion): Separates by hydrodynamic volume/size; larger proteins elute first as they can’t enter gel pores.

Introduction to Protein Separation

Proteins separated by size techniques are essential in biochemistry for purifying and analyzing mixtures based on molecular weight. These methods, like SDS-PAGE, help researchers isolate proteins for studies in molecular biology and proteomics.

Size-Based Methods

Proteins separated by size techniques include gel electrophoresis and chromatography that differentiate by mass.

Applications and Choices

Use SDS-PAGE for quick visualization or gels; size-exclusion for native proteins in columns. Non-size methods like isoelectric focusing pair well in 2D electrophoresis for complex samples.