Question

Which statement best explains why Phosphofructokinase \((PFK-1)\) is considered the major regulatory enzyme of glycolysis?

• A. It catalyzes only ATP producing step in glycolysis
• B. It controls the first irreversible step that commits glucose to glycolysis
• C. It converts pyruvate into lactate under anaerobic condition
• D. It is the final enzyme of glycolysis and regulates ATP yield

Hint:

PFK-1 is the key regulatory enzyme of glycolysis because it catalyzes the committed irreversible step: fructose-6-phosphate to fructose-1,6-bisphosphate.

Answer 1

The Correct Option is B

Concept:
Glycolysis is the pathway that breaks down glucose to pyruvate. Some steps are reversible, while some are irreversible and highly regulated.

Step 1: Role of PFK-1.
PFK-1 catalyzes the conversion of fructose-6-phosphate into fructose-1,6-bisphosphate. \[ \text{Fructose-6-phosphate} \rightarrow \text{Fructose-1,6-bisphosphate} \]

Step 2: Why this step is important.
This is a committed step of glycolysis. Once fructose-6-phosphate is converted into fructose-1,6-bisphosphate, the molecule is committed to proceed through glycolysis.

Step 3: Regulation of PFK-1.
PFK-1 is regulated by cellular energy status. ATP inhibits PFK-1, while AMP and fructose-2,6-bisphosphate activate it.

Step 4: Eliminate wrong options.
PFK-1 does not catalyze an ATP-producing step. Pyruvate to lactate conversion is done by lactate dehydrogenase. PFK-1 is not the final enzyme of glycolysis. Therefore, PFK-1 is the major regulatory enzyme because: \[ \text{It controls the first committed irreversible step of glycolysis.} \] \[ \therefore \text{Correct Answer is (B)} \]