In glycolysis, the first committed step is catalysed by-
## Core Concept
The first committed step in glycolysis refers to the initial irreversible reaction that commits glucose to being broken down through the glycolytic pathway. This step is crucial as it ensures that glucose is utilized efficiently by cells for energy production.
## Why the Correct Answer is Right
The correct answer, **Phosphofructokinase-1 (PFK-1)**, catalyzes the conversion of fructose-6-phosphate into fructose-1,6-bisphosphate. This step is considered the first committed step of glycolysis because it is irreversible under physiological conditions and commits the glucose molecule to being metabolized through glycolysis. PFK-1 is a key regulatory enzyme in glycolysis, influenced by various factors including ATP, citrate, and AMP levels, making it a critical point of control.
## Why Each Wrong Option is Incorrect
* **Option A:** Hexokinase catalyzes the conversion of glucose to glucose-6-phosphate, which is an early step but not considered the first committed step because glucose-6-phosphate can still be utilized in other pathways, such as the pentose phosphate pathway or glycogen synthesis.
* **Option B:** Phosphoglucomutase is involved in glycogen synthesis, converting glucose-6-phosphate to glucose-1-phosphate, and is not a part of glycolysis.
* **Option D:** Pyruvate kinase catalyzes the final step of glycolysis, converting phosphoenolpyruvate (PEP) to pyruvate, which is not the first committed step.
## Clinical Pearl / High-Yield Fact
A key clinical correlation is that **PFK-1 deficiency** leads to a rare genetic disorder known as Tarui's disease, characterized by glycogen storage disease type VII. This condition highlights the importance of glycolytic enzymes in energy metabolism.
## Correct Answer: C. Phosphofructokinase-1 (PFK-1).