Gluconeogenesis, must bypass irreversiblereactions of glycolysis, except:a. Hexokinaseb. Phosphohexose isomerasec. Pyruvate kinased. Phosphofructokinase

Sure, let's break down the question step by step.

Understanding the Question

The question is asking which enzyme's reaction in glycolysis does not need to be bypassed during gluconeogenesis.

Key Concepts

1. Glycolysis: A metabolic pathway that converts glucose into pyruvate, generating ATP and NADH in the process. It consists of a series of enzymatic reactions.
2. Gluconeogenesis: The process of synthesizing glucose from non-carbohydrate precursors. It essentially runs glycolysis in reverse but must bypass the irreversible steps of glycolysis.
3. Irreversible Reactions in Glycolysis: There are three key irreversible steps in glycolysis, catalyzed by the following enzymes:
   • Hexokinase (or Glucokinase in the liver)
   • Phosphofructokinase-1 (PFK-1)
   • Pyruvate kinase

The Enzymes Listed

a. Hexokinase: Catalyzes the phosphorylation of glucose to glucose-6-phosphate. This is an irreversible step. b. Phosphohexose isomerase: Catalyzes the conversion of glucose-6-phosphate to fructose-6-phosphate. This is a reversible step. c. Pyruvate kinase: Catalyzes the conversion of phosphoenolpyruvate (PEP) to pyruvate. This is an irreversible step. d. Phosphofructokinase (PFK-1): Catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate. This is an irreversible step.

Analysis

• Hexokinase: Irreversible, must be bypassed in gluconeogenesis.
• Phosphohexose isomerase: Reversible, does not need to be bypassed.
• Pyruvate kinase: Irreversible, must be bypassed in gluconeogenesis.
• Phosphofructokinase (PFK-1): Irreversible, must be bypassed in gluconeogenesis.

Conclusion

The enzyme whose reaction does not need to be bypassed during gluconeogenesis is b. Phosphohexose isomerase.