Question

QUESTION 21 Which of these enzymes is not involved in both glycolysis and gluconeogenesis Phosphoglycerate kinase Enolase Aldolase Phosphohexose isomerase Fructose-1,6-bisphosphatase

i need right answers for these four questions please as I am stuck in it. thank you so much

Answer 1

Question 21

Answer: Fructose-1,6-bisphosphatase

The conversion of Fructose-1,6-bisphosphate to Fructose-6-phosphate in gluconeogenesis is catalyzed by the enzyme Fructose-1,6-bisphosphatase while the opposite reaction occuring in glycolysis is calalyzed by Phosphofructokinase. The Fructose-1,6-bisphosphatase enzyme is absent in glycolysis.

All other enzymes are present in both glycolysis and gluconeogenesis and catalyze reactions in opposite direction.

Question

Answer: Gluconeogenesis is simply the reverse of glycolysis

Gluconeogenesis is not exactly the reverse of glycolysis. Three steps differ in them and use different enzymes. The conversion of Phosphoenolpyruvate to Pyruvate is catalyzed by Pyruvate kinase in glycolysis while the opposite reaction in gluconeogenesis is catalyzed by two enzymes (pyruvate carboxylase and pyruvate carboxykinase) and involves Oxaloacetate as an intermediate. Similarly, the conversion of Fructose-1,6-bisphosphate to Fructose-6-phosphate is catalyzed by Fructose-1,6-bisphosphatase while the opposite reaction in glycolysis is catalyzed by Phosphofructokinase. Also, the conversion of glucose to glucose-6-phosphate is catalyzed by Hexokinase (or Glucokinase) in Glycolysis while the opposite reaction in gluconeogenesis is catalyzed by Glucose-6-phosphatase.

Glycolysis breaks down a large glucose molecule into smaller pyruvate molecules and is catabolic, Gluconeogeneis does the opposite and is thus anabolic.

The four enzymatic reactions mentioned above are unique to Gluconeogenesis.

Gluconeogenesis syntheisizes glucose from pyruvate.

Question 25

Answer: Glucose-6-phosphate

Since the conversion of glucose-6-phosphate to glucose is catalyzed by Glucose-6-phosphatase, the absence of this enzyme will cause the accumulation of the substrate which is glucose-6-phosphate.

No other option given in question is the substrate of the enzyme glucose-6-phosphatase.

Question 26

Answer: It decreases glycolytic activity

The enzyme Hexokinase involved in glycolysis is allosterically regulated by the glucose-6-phosphate which is the product formed by the enzyme. Higher the concentration of glucose-6-phosphate, lower becomes the activity of the Hexokinase enzyme due to a negative feedback mechanism. Thus, glycolysis will be slowered down by glucose-6-phosphate accumulation.

Since the feedback is negative, it cannot increase the glycolytic activity.

Also, it downregulates the Hexokinase activity but cannot completely stop it. Thus, cannot completely stop glycolysis.

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