Question

Which of the following is the principle reason that gluconeogenesis does not occur in muscle cells..

1) cofactors required for gluconeogenesis are absent from muscle cells

2) one or more intermediates of the gluconeogenesis pathway are absent from muscle cells

3) Gluconeogenesis is highly unfavorable in muscle cells

4) Muscle cells use allosteric regulation to prevent gluconeogensis

5) Rate of gluconeogenesis is zero

Answer 1

2.) One or more intermediates of the gluconeogenesis pathway are absent from muscle cells.

Gluconeogenesis is the synthesis of Glucose from non-carbohydrate precursors which occurs in the liver of animals. The major difference between Gluconeogenesis and Glycolysis are the irreversible steps. First irreversible step in glycolysis is the conversion of Fructose 6- phosphate into Fructose-1,6-bisphosphate, this reaction is mediated by Phosphofructokinase(PFK). So during gluconeogenesis enzyme 1,6 bisphosphatase acts without using ATP and converts Fructose 1,6 bisphosphate into fructose 6 phosphate.

Another step of glycolysis is where Glucose is converted into Glucose-6-phosphate by Hexokinase enzyme/ this reaction is also irreversible. During Gluconeogenesis, conversion of G-6-phosphate into Glucose is done by Glucose-6-Phosphatase. This enzyme is present in the endoplasmic reticulum membrane of liver and kidney cells. But it is absent in the muscle cells and brain cells. For this reason gluconeogenesis does not occur in the muscle an brain.