Question

During glycolysis, if the enzyme pyruvate kinase that converts phosphoenolpyruvate to pyruvate is inhibited, how many direct ATPs are produced per glucose molecule?

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

The correct option is B 2

The pathway of the breakdown of glucose into pyruvic acid is termed as glycolysis. This pathway is a step-wise process in which several molecules are released like 4 ATPs, 2 ADPs, water and 2 (NADH+ $H^{+}$) when the reactant intermediates undergo a reaction. The steps are given below:


The penultimate step of glycolysis is catalysed by pyruvate kinase. A phosphate from phosphoenolpyruvate is transferred to ADP to form pyruvate and ATP by the action of pyruvate kinase. Two molecules of pyruvate and ATP are obtained as the end products if one glucose molecule undergoes glycolysis.

Since this last step is inhibited due to the inhibition of pyruvate kinase, there will be no ATP or pyruvate production in the last step. So, only two direct ATPs are produced overall per glucose molecule. These two ATPs are produced during the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate.