Question

QUESTION 3 The B2 resource mentions that magnesium is always complexed with ATP in the cell. The standard free energy change of ATP hydrolysis, AGº'= -30.5 kJ/mol, was determined in the presence of magnesium. The AGº for ATP hydrolysis in the absence of Mg2+ is -35.7 kJ/mol. This suggests that Mg2+ stabilizes ATP, thus lowering its AGO'. Select the change in the factor that is most likely responsible for the lessening of the free energy difference between ATP and its hydrolytic products. O Electrostatic repulsion O Resonance stabilization O Increase in entropy O Stabilization due to hydration

Answer 1

Answer 3:

Option 'electrostatic repulsion' is correct.

• As the substrate of the enzyme is MgATP^2- complex and not ATP^4- .
• Mg²⁺ shields the negative charges of the phosphoryl groups in ATP.
• Thus the terminal phosphorus atom becomes an easier target for nucleophilic attack.
• It brings conformational change in enzyme.
• Hence change in electrostatic repulsion is responsible for lessening of the free energy difference between ATP and its hydrolytic product.