You can make a cell extract that is able to perform glycolysis in vitro (in a test tube) if glucose is added. Arsenate is a potent inhibitor of triose phosphate dehydrogenase, the enzyme required for the 6th step in glycolysis. If both arsenate and glucose are added to the cell extract, what happens?

a. ATP levels decrease.

b. Both ATP and pyruvate levels decrease.

c. Both ATP and pyruvate levels increase.

d. ATP levels increase.

Answer: B

Explanation:

If glucose and arsenate are both added to the cell extract, at first glycolysis will start.

In step one of glycolysis, glucose is phosphorylated to glucose-6-phosphate catalyzed by hexokinase which splits the ATP into ADP, and the Pi is added on to the glucose.

In step 3 of glycolysis, fructose-6-phosphate is further phosphorylated to fructose 1,6-bisphosphate. The enzyme is phosphofructokinase. This again involves hydrolysis of another ATP molecule.

A total of two ATP is used.

Step 6 in glycolysis reaction which involves generation of 2 ATP's molecules is inhibited by arsenate. Hence all other glycolytic reaction would not take place. Therefore no ATP is produced and pyruvate is not produced also.

ATP level decreases because ATP is only used up but no ATP is gained from the inhibited pathway. Also the inhibition of the step 6 enzyme cut short the pathway and pyruvate the end product of the pathway is not formed.