Question

Which of the following components bind to the solid column made of silica, under high salt concentration?

• A. Proteins
• B. Polysaccharides
• C. Both proteins and polysaccharides
• D. Plasmid DNA

Hint:

High salt conditions can enhance binding in chromatography by neutralizing the charges on molecules, allowing them to interact with the silica surface.

Answer 1

The Correct Option is C

High salt concentration reduces the electrostatic repulsion between a biomolecule's surface charges and the silica matrix by shielding those charges with counterions, letting the molecule adsorb onto the silica surface.

This shielding effect is not specific to one type of biomolecule: proteins carry surface charges from ionizable side chains, and polysaccharides carry charges from hydroxyl and, in some cases, acidic sugar groups -- both get shielded the same way under high salt and can bind the silica surface.

Because the mechanism applies to both classes together rather than to just one, the correct choice is both proteins and polysaccharides.

Answer 2

Another way to approach this is by process of elimination based on what distinguishes each answer choice from the others.

1. Proteins: This option only accounts for one class of biomolecule, leaving out a second class that behaves the same way under these conditions, so it is incomplete on its own.
2. Polysaccharides: Likewise, this option only names one class of molecule and omits the other class that also binds under the same high-salt principle.
3. Both proteins and polysaccharides: This option is the only one that captures the full picture, since both classes of macromolecule interact with the silica surface once their charges are shielded by high salt.
4. Plasmid DNA: This introduces a nucleic acid, a different category of macromolecule from the two under discussion, and does not correspond to the pairing the question is testing.

Since options 1 and 2 are each only partially correct and option 4 shifts to an unrelated molecule, the option that fully addresses the question is the one combining both classes.

Hence, the correct answer is both proteins and polysaccharides.