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Understanding the Hydrophobic Effect in Protein Folding

Question: What contributes the most towards the hydrophobic effect when a protein is folding at room temperature?

Options:

1. Entropy of the water molecules

2. Entropy of the protein molecules

3. Entropy of the protein chain

4. Free energy of interaction between the protein residues

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Correct Answer:

1. Entropy of the water molecules

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Detailed Explanation:

The hydrophobic effect is a major driving force in the folding of globular proteins, and it primarily arises due to the behavior of water molecules surrounding hydrophobic (non-polar) residues.

Here’s how it works:

• Hydrophobic residues tend to avoid water. When they are exposed to an aqueous environment, water molecules form an ordered “cage” around them to minimize disruption of hydrogen bonding networks.

• This ordering of water decreases entropy, which is thermodynamically unfavorable.

• To minimize this entropy loss, the protein folds in such a way that hydrophobic residues are buried inside, away from water.

• As a result, water molecules are released and become disordered again, increasing entropy of the system, which is thermodynamically favorable.

Thus, the increase in entropy of water molecules upon burial of hydrophobic residues is the main contributor to the hydrophobic effect during protein folding.

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Conclusion:

The entropy of water molecules, not of the protein itself, is the dominant factor in driving the hydrophobic effect that facilitates protein folding at room temperature. This entropic gain is crucial for stabilizing the native, folded state of a protein in aqueous environments.