Question

Explain the chemical logic of dehydrating 2-phosphoglycerate before its phosphoryl group is transferred.

Short answer

The dehydration of 2-phosphoglycerate forms phosphoenolpyruvate (PEP), a compound with high phosphoryl group transfer potential. This enables it to transfer a phosphate to ADP for ATP formation.

Step-by-step solution

Conversion of 2-phosphoglycerate to phosphoenolpyruvate

2-phosphoglyceric acid, also known as 2-phosphoglycerate, is aglyceric acid that acts as a substrate in the ninth glycolysis reaction. Enolase catalyzes the conversion of 2-phosphoglycerate into phosphoenolpyruvate.

Chemical logic of phosphoryl group

The typical free energy of 2-phosphoglycerate hydrolysis is -16kJ/mol, which is not sufficient to fuel ATP formation from ADP. However, when 2-phosphoglycerate is dehydrated, a high-energy molecule PEP is formed that can be used in ATP formation. PEP has a high phosphoryl group transfer potential, which allows it to transfer a phosphate group to ADP and produce ATP.

Thus, when 2-phosphoglycerate is dehydrated, a high-energy molecule PEP is formed.