Question

6. Free Energy Calculation (10 pts) Ribonuclease-A (RNase-A), a digestive enzyme hydrolyzes RNA to its component nucleotides. An inhibitor of the enzyme, 2'-cyclic monophosphate, can be used to study the enthalpy of nucleotide binding to RNase-A. The scheme showing below is based on the isolation of 2',3'-cyclic nucleotides from RNase A digests of RNA. There are four types of 2,3'-cyclic nucleotides. RNase-A hydrolysis of one of them, cytidine 2',3'-cyclic phosphate, has been studied extensively. The reaction is given as:

Answer 1

The entropy changes have been determined at 25°C. The overall ΔS° for this reaction is 6.6 cal mol-1 K-1. ΔH° for the reaction is -2800 cal mol-1. Thus by using the equation

                                                         ΔG° = ΔH°- T ΔS° (T = 298 K)

The free energy change is -4800 cal mol-1. The reaction is a spontaneous reaction since free energy change is negative