Entropy of Solvation Layers/ Protein Folding

[ScrubswithnoSleeves]

I'm having some difficulty understanding this problem from my Kaplan full length. (pic attached)

I would think that because the non-polar proteins are clustering (much like folding the non-polar R-groups inwards) that it is becoming more ordered and thus entropy would be decreasing. Also, I would think that a solvation layer would also reduce the entropy of the system.

From a spontaneity stand point I get it. ∆G = ∆H - T∆S, so ∆S must be large and positive for the reaction to be spontaneous, which of course it is.

Can someone please explain this concept to me? Do I not understand entropy??

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[aldol16]

Entropy involves the disorder of the entire system and not just the protein. The only requirement of the second law is that entropy in the universe must increase. Therefore, the entropy of the system equals the entropy of the protein plus the entropy of the water molecules around it. If the protein is in extended conformation, the water is arranged in a highly-ordered solvation layer around the protein and thus the overall entropy of the system is reduced. When a protein folds, the waters around it are released and the solvation layer can be much smaller, thereby driving an increase in entropy of the system. We know that since proteins like to fold, the change in entropy of the water solvation layer must be greater than the reduction in entropy of the protein upon folding.

 

[ScrubswithnoSleeves]

Entropy involves the disorder of the entire system and not just the protein. The only requirement of the second law is that entropy in the universe must increase. Therefore, the entropy of the system equals the entropy of the protein plus the entropy of the water molecules around it. If the protein is in extended conformation, the water is arranged in a highly-ordered solvation layer around the protein and thus the overall entropy of the system is reduced. When a protein folds, the waters around it are released and the solvation layer can be much smaller, thereby driving an increase in entropy of the system. We know that since proteins like to fold, the change in entropy of the water solvation layer must be greater than the reduction in entropy of the protein upon folding.

So overall, the entropy of the protein itself has decreased but the entropy of the water molecules has increased by a larger amount and thus the total entropy of the system is positive. Is that correct?

 

[aldol16]

So overall, the entropy of the protein itself has decreased but the entropy of the water molecules has increased by a larger amount and thus the total entropy of the system is positive. Is that correct?

That is correct.