Question

Concentrations of some glycolysis intermediates in the red blood cell (mM): Glucose Glucose-6-P Fructose-6-P Fructose-1,6-BP 1,3-bisphosphoglycerate 0.001 3-phosphoglycerate 5.0 0.083 0.014 0.031 2- phosphoglycerate Phosphoenolpyruvate Pyruvate ATP ADP Pi 0.030 0.023 0.051 1.85 0.14 1.0 0.12 3. Isotopic labeling (incorporating a rare isotope, eg. the radioactive 1C, into a molecule at a defined position) is an important technique for studying metabolism as it enables us to follow individual atoms through a metabolic pathway 2 a. If 4CO2 were bubbled through a suspension of liver cells that was undergoing gluconeogenesis, which carbons in the glucose molecule would become radioactive? Briefly explain your reasoning. (2 marks) b. Suppose that we could label glucose with 1C at any position or combination of positions. For yeast fermenting glucose to ethanol, which position(s) in the glucose molecule would have to be labeled in order to give the most radioactivity in ethanol and the least in CO2? Justify your reasoning. (3 marks) но он он он glucose

Answer 1

1.Gluconeogenesis is a metabolic process which produces glucose from the non-carbohydrate substrates.

Labelled carbon dioxide bubbled through the liver cell suspension will react with water and produce bicarbonate ion which is being utilized in the first step of gluconeogenesis. Here (reaction 1 given below) utilizing ATP, the labelled carbon of bicarbonate reacts with pyruvate and forms the fourth carboxyl group of oxaloacetate. But in the next step, the terminal labelled carboxyl carbon is being removed again as carbon dioxide utilizing GTP to form pyruvate.

Thus, none of the carbon will be C¹⁴ labelled in the newly formed glucose from gluconeogenesis.

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