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

Step 1: Understanding the question.
In the presence of high salt concentration, both proteins and polysaccharides can bind to silica columns due to their charge interactions and affinity for the surface. This technique is commonly used in chromatography to separate biological molecules.
Step 2: Analyzing the options.
(1) Proteins: Proteins can bind to silica under specific conditions, but this is not the full answer as polysaccharides also bind.
(2) Polysaccharides: Polysaccharides also bind to silica but not exclusively; proteins play a role too.
(3) Both proteins and polysaccharides: Correct — Both proteins and polysaccharides bind to silica under high salt conditions in chromatography processes.
(4) Plasmid DNA: Plasmid DNA typically does not bind to silica unless specific conditions are applied, such as in DNA purification protocols.
Step 3: Conclusion.
The correct answer is (3) Both proteins and polysaccharides, as both components interact with silica under high salt conditions.

Answer 2

Binding to a silica matrix under high salt conditions depends on how well a molecule's charged groups are shielded by the surrounding ions, allowing it to associate with the silica surface. Let's go through each option with that lens.

1. Proteins: Under high salt, counterions in solution shield the charged and polar groups on a protein's surface, reducing electrostatic repulsion between the protein and the silica surface and allowing it to associate with the matrix. This shows proteins alone can bind under these conditions.
2. Polysaccharides: Polysaccharides carry numerous hydroxyl and, in some cases, charged groups that behave the same way -- high salt concentration masks their surface charge and permits interaction with silica.
3. Both proteins and polysaccharides: Since the same underlying principle (charge shielding by high salt promoting adsorption onto silica) applies to both classes of molecule, neither can be excluded on its own; the binding behaviour described applies to both together.
4. Plasmid DNA: This option restricts the answer to only one type of biomolecule, while the question is asking specifically about which everyday macromolecule classes bind under high salt in this general context, which points to the two classes already covered rather than DNA alone.

Since the identical salt-shielding mechanism applies equally to proteins and to polysaccharides, restricting the answer to just one of them or to a different molecule altogether misses the complete picture.

Therefore, the correct answer is both proteins and polysaccharides.