Question

In detail, please describe gluconeogenesis in simple terms, describe what the difference is between it and why it's not reverse glycolysis, and descirbe it's first bypass (bypass 1) in mitochondria.

Answer 1

Gluconeogenesis :

Glucose synthesis from non carbohydrate compounds : Lactate, pyruvate, glucogenic amino acids( alanine, glutamine, asparagine etc. ) , propionate & glycerol) is known as gluconeogenesis.

Difference between gluconeogenesis and glycolysis :

Pathway of gluconeogenesis is almost similar to reverse to glycolysis. However, there are 3 irreversible steps in glycolytic pathway :

1) Glucose ------> Glucose 6-phosphate

2) Fructose 6-phosphate -----> Fructose 1,6-bisphosphate

3) Phosphoenolpyruvate (Pep) ----> Pyruvate.

These steps are catalyzed by class of enzymes: kinases ( Kinase , phosphofructokinase & pyruvate kinase) in glycolytic pathway. However, there are different enzymes for reverse of these steps in case of gluconeogenesis.

First bypass in mitochondria :

Conversion of pyruvate to phosphoenolpyruvate is first step in pathway of gluconeogenesis. However, it is 1 of the 3 irreversible steps in glycolysis catalyzed by enzyme pyruvate kinase. Thus, in gluconeogenesis there is bypass of this step with help of other enzyme known as pyruvate carboxylase.

Conversion of pyruvate to phosphoenolpyruvate occurs in 2 steps:

1) Conversion of pyruvate to oxaloacetate in mitochondrial matrix :

ATP 了 Co2 COO-CH,-C-COO 3 Loxaloaceta-te) ades ан bori lose 2

ATP 了 Co2 COO-CH,-C-COO 3 Loxaloaceta-te) ades ан bori lose 2

ATP 了 Co2 COO-CH,-C-COO 3 Loxaloaceta-te) ades ан bori lose 2

2) Transport of oxaloacetate to cytosol and conversion of oxaloacetate to phosphoenolpyruvate :

oxaloacetate is not able to cross the mitochondrial matrix. Also, it should be transported to cytosol so that it would be available for gluconeogenesis. Thus, it is first converted to maltate. Maltate crosses the mitochondrial matrix. After reaching cytosol, it converts back to oxaloacetate.

In cytosol, oxaloacetate upon acted by enzyme phosphoenolpyruvate carboxykinase gives rise to phosphoenolpyruvate :

C-CoD TP CH (PEP) car bony kinase.

Pathway of gluconeogenesis :

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