Many biological macromolecules andergo a transition called denaturation. Denatur

Question

Many biological macromolecules andergo a transition called denaturation. Denaturation is a process whereby a structured, biologically active molecule, called the native form, unfolds or becomes unstructured and biologically inactive. The equilibrium shown below. (Prof. Sarah Keller) For a protein at pH=2, the enthalpy change associated with denaturation is Delta Hdegree=418 kJ/mol and the entropy change is Delta S degree=1.3 kJ K^-1 mol^-1. Calculate the Gibbs energy change for the denaturation of the protein at pH=2 and T=303 K. Assume the enthalpy and entropy are temperature independent between 298 K and 303 K. Calculate the equilibrium constant for the denaturation of protein at pH=2 and T = 303 K. Based on your answers for parts a) and b), is protein structurally stable at pH=2 and T=303 K?

Explanation / Answer

a. dGo = dHo - TdSo

Feed given values,

Gibbs free energy dG would be,

dGo = 418 - 303 x 1.3 = 24.1 kJ/mol

b. dGo = -RTlnKeq

24.1 x 1000 = -8.314 x 303 lnKeq

Equilibrium constant for denaturation Keq would be,

Keq = 7.00 x 10^-5

c. The protein structure is stable at pH 2 and T = 303 K

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