A certain biosynthetic transformation converts substrate S to product P through the…
CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
A certain biosynthetic transformation converts substrate S to product P through the two consecutive standard-state steps shown below.
Step 1 S + ATP → S-P + ADP ΔG° = −30.5 kJ mol⁻¹
Step 2 S-P → P + Pi ΔG° = +18.6 kJ mol⁻¹
A researcher wants to know how many moles of ATP must be available so that 2.00 mol of product P can be formed under standard-state conditions with no net positive free-energy change.
(a) Combine the two steps to write the overall reaction for the conversion of S to P, omitting intermediates, and calculate the overall ΔG° (in kJ mol⁻¹).
(b) Determine the minimum number of moles of ATP that must be hydrolyzed (via Step 1) to drive the formation of 2.00 mol of P under standard-state conditions, assuming 100 % efficiency.
(c) If only 1.50 mol of ATP is on hand, calculate the maximum number of moles of P that can be produced. Show your reasoning.
(d) Propose one strategy a cell might employ, other than increasing ATP supply, to drive the reaction toward product formation, and briefly explain how that strategy affects the free-energy change.