Question

2. In gluconeogenesis, it takes two enzymes to convert pyruvate to phosphoenolpyruvate. a. Explain what is happening chemically to the substrates in these two reactions.

Answer 1

Answer:1. Pyruvate carboxylase

2. Phosphoenol pyruvate carboxy kinase

Explanation:

The conversion of pyruvate to phosphoenol pyruvate is catalyzed by two enzymes Pyruvate carboxylase and phosphoenol pyruvate carboxy kinase

1. Pyruvate carboxylase reaction

Pyruvate in the cytoplasm enters the mitochondria. Then, carboxylase of pyruvate to oxaloacetate is catalysed by a mitochondrial enzyme, pyruvate carboxylase. It needs the co-enzymes biotin and ATP.

The oxaloacetate formed has to be transported from the mitochondrial to the cytosol because further reaction of gluconeogenesis are taking place in cytosol.

2. Phoaphoenol pyruvate carboxy kinase (PEPCK)

In the cytoplasm, PEPCK enzyme then converts oxaloacetate to phoaphoenol pyruvate by removing a molecule of CO2. GTP or ITP donates the phosphate group.

The net effect of these two reactions is the conversion of pyruvate to phoaphoenol pyruvate. This circumverts the irreversible step in glycolysis catalyzed by pyruvate kinase (step 9 if glycolysis)