Question

Starch is a polymer of glucose molecules in plants with a role analogous to that of glycogen in animals. Starch synthesis requires ADP‑glucose generated by ADP‑glucose pyrophosphorylase. The biochemical mechanism of ADP‑glucose pyrophosphorylase catalysis is similar to that of UDP‑glucose pyrophosphorylase. What is the driving force for the ADP‑glucose pyrophosphorylase reaction?

a. production of ADP‑glucose
b. hydrolysis of ADP‑glucose
c. production of pyrophosphate
d. hydrolysis of pyrophosphate

Answer 1

The driving force for the ADP-glucose pyrophosphorylase reaction is hydrolysis of pyrophosphate.

Step-by-step explanation:

The driving force for the ADP‑glucose pyrophosphorylase reaction is d. hydrolysis of pyrophosphate.

Here's why:

The reaction is:

ATP + glucose-1-phosphate + pyrophosphate <=> ADP-glucose + phosphate

The hydrolysis of pyrophosphate (PPi) into two inorganic phosphates releases a significant amount of free energy (approximately -30 kJ/mol). This free energy release drives the reaction forward, even though the difference in free energy between ADP-glucose and ATP is small.

The production of ADP-glucose (a readily usable sugar precursor) is important for starch synthesis, but it is the hydrolysis of PPi that provides the necessary energy for the reaction to occur.

Therefore, option d is the correct answer.The driving force for the ADP‑glucose pyrophosphorylase reaction is production of ADP-glucose.