Metabolic steps that are thermodynamically unfavorable can be driven forward by

a) Coupling the reaction to ATP hydrolysis

b) High substrate and low product concentrations

c) Low Substrate and high product concentrations

d) A and B

e) A and C

d) A and B

Explanation:

A metabolic step/reaction is said to be thermodynamically unfavorable if ΔG of that reaction is positive and if ΔG is negative then process is thermodynamically favorable. Thermodynamically favorable simply means that the reaction will be spontaneous i. e. it will occur on its own.

If a metabolic step is thermodynamically unfavorable it can easily be made favorable by coupling it with ATP hydrolysis. In ATP hydrolysis, ATP is broken down into ADP + Pi to produce ΔG = - 7.3 kcal/mole. This negative value of ΔG makes the unfavorable step to move forward.

Apart from this, high substrate and low product concentrations also play important role in making an unfavorable reaction to move forward by increasing rate of reaction. At high substrate concentrations, enzymes have ample substrate present all around and enzyme's active site is never free that means enzyme-substrate complex will be formed constantly resulting into increased rate of reaction in forward direction. At low product concentrations, there is no chance of attainment of equilibrium and reaction has tendency to move only in forward direction.