Question

In glycolysis two ATPs are generated at two different steps in stage two. The creation of ATP from ADP has a free energy change of +30.5 kJ/mol. Explain how this energy barrier is overcome for the metabolic process to proceed through these two steps?

Answer 1

Substrate level phosphorylation: It is a metabolic reaction takes place during different metabolic pathways that result in the formation of ATP (or GTP) by converting a higher energy substrate into a lower energy product by using released chemical energy.

There are two steps in which the creation of ATP from ADP has a free energy change of +30.5 kJ/mol. These reactions are known as substrate-level phosphorylation. The reactions are a part of the second-half of glycolysis and involved in energy-releasing steps.

1) The first substrate-level phosphorylation takes place when 1,3-bisphosphoglycerate is converted into 3-phosphoglycerate that involves dephosphorylated of 1,3-bisphosphoglycerate via phosphoglycerate kinase, producing ATP through substrate-level phosphorylation.

2) The second substrate-level phosphorylation occurs by dephosphorylating phosphoenolpyruvate, catalyzed by pyruvate kinase, producing pyruvate and ATP.

Thus, the energy barrier is overcome for the metabolic process to proceed through these two steps because of the formation of ATP by the physical addition of a phosphate group to ADP from the substrate. The barrier is crossed because the phosphate group is transferred from the substrate and there is no requirement of any other source for the phosphate. The breakdown of phosphate release the energy to carry out the reaction that is the chemical energy.