Question

Glycolysis is the process by which energy is harvested from glucose by living things. Several of the reactions of glycolysis are thermo dynamically unfavorable (nonspontaneous), but proceed when they are coupled with other reactions.
Which of the following reaction is unfavorable?
Reaction A: Pi+glucose⟶glucose-6-phosphate+H2OΔG=13.8 kJ/mol
Reaction B: Pi+fructose-6-phosphate⟶fructose-1,6-bisphosphate+H2OΔG=16.3 kJ/mol
Reaction C: ATP+H2O⟶ADP+PiΔG=−30.5 kJ/mol Select every unfavorable reaction.

Answer 1

Answer: Reaction A: pi + glucose ⇒ glucose-6-phosphate + H2O ΔG = 13.8 kJ/mol

Reaction B: pi + frutose-6-phosphate ⇒fructose-1,6-biphosphate + H2O ΔG = 16.3kJ/mol

Explanation: ΔG is the representation of the change in Gibbs Free Energy and relates enthalpy and entropy in a single value, which is:

ΔG = ΔH - TΔS

where:

ΔH is enthalpy

T is temperature

ΔS is entropy (measure of the )

It can also predict the direction of the reaction with the conditions of temperature and pressure being constant.

When the change is positive, the reaction is non-spontaneous, which means the reaction needs external energy to occur. If the change is negative, it is spontaneous, i.e., happens without external help.

Analyzing the reaction, we see that reaction A and B have a positive ΔG, while reaction C is negative, so the reaction that are unfavorable or nonspontaneous are reactions A and B.