Question

Assume that some protein molecule, in its folded native state, has one favored conformation. But when it is denatured, it becomes a "random coil", with many possible conformations.

How will the contribution of ΔS for native → denatured affect the favorability of the process? What apparent requirement does this impose on ΔH if proteins are to be stable structures?

Answer 1

Gibbs Free Energy is given by the next equation: ΔG = ΔH - TΔS, where

ΔH - change in enthalpy

T - temperature in Kelvin

ΔS - change in entropy

ΔG can be:

• ΔG>0 positive(not spontaneous reaction)
• ΔG<0 negative(spontaneous reaction)
• ΔG=0(in equilibrium).

→ When the proteins are denatured, the entropy of the system increases. Therefore, the ΔS also increases and becomes more positive.

→ From the equation we see that positive value of ΔS contributes to negative value of ΔG.

The proteins are stable when there is no spontaneous reaction, thus, the ΔG>0 is required. Which means that ΔH has to be large and positive to counteract the influence of ΔS.