Answer :
The question asks about the mechanisms that prevent glycolysis and gluconeogenesis from occurring simultaneously in cells. Both glycolysis and gluconeogenesis are metabolic pathways involved in glucose metabolism, but they have opposite effects. Glycolysis breaks down glucose to produce energy, while gluconeogenesis creates glucose from non-carbohydrate precursors.
Here are the main reasons that prevent these two processes from occurring at the same time:
Key Regulatory Enzymes that are Irreversible (C):
- Both pathways have key enzymes that are unique to each process and are irreversible. In glycolysis, these include hexokinase, phosphofructokinase, and pyruvate kinase. In gluconeogenesis, enzymes like pyruvate carboxylase, phosphoenolpyruvate carboxykinase, and fructose 1,6-bisphosphatase are critical. These enzymes are regulated differently, ensuring that only one pathway is active at a time.
Bypass Pathways Proceeding Through Different Intermediates (B):
- While most reactions in glycolysis and gluconeogenesis are the reverse of each other, the pathways are not mere reversals because certain steps are bypassed using different intermediates. This strategic difference further ensures that the pathways do not operate simultaneously.
The correct answer is C) Key regulatory enzymes that are irreversible. These enzymes are crucial in controlling the flux through these pathways and are regulated by various means, such as allosteric regulation and hormonal control, to ensure that glycolysis and gluconeogenesis do not function at the same time, preventing a futile cycle.
Overall, this regulatory mechanism is essential because it conserves energy for the cell and maintains proper glucose levels.
