a. Gluconeogenesis occurs in cells in response to low glucose levels. You want t

Question

a.   Gluconeogenesis occurs in cells in response to low glucose levels. You want to know if your particular

cell line undergoes gluconeogenesis and therefore, compare cells grown in normal medium to those

grown in very low glucose levels (starvation). What metabolites and enzyme activity do you look for to

confirm gluconeogenesis is occurring? How would you effectively inhibit gluconeogenesis?

b.   Gluconeogenesis and glycolysis are both overall thermodynamically favorable in the cell. Given one is

basically the reverse of the other, with many common enzymes and reversible reactions, how can this

be?

Explanation / Answer

a)If we see PKA level and glucagon level then we can be confirmed if gluconeogenesis is occuring or not. Higher concentration of NADH will inhibit gluconeogenesis. Higher ethanol concentration will easily do the task.

b) During glycolysis glucose is oxidized to pyruvate. The synthesis of glucose from pyruvate occurs in gluconeogenesis. So gluconeogenesis is a reverse pathway to glycolysis.Since the process of converting glucose to pyruvate via glycolysis is energy releasing, the reverse reaction requires energy. Most of the steps in gluconeogenesis pathway have a Gibbs free energy of nearly zero and are easily reversed by slight changes in the concentration of products and reaction. But there are 3 steps in glycolysis that requires such huge decrease in energy that they cannot be spontaneous in the reverse direction.

The first 2 reaction in glycolysis use ATP to drive an otherwise nonfavorable reaction, the phosphorylation of sugars , the simpler reverse reaction ,hydrolysis , will be favorable & spontaneous. Consequently in gluconeogenesis these two steps are catalyzed by phosphatase instead of kinases.

The 3rd reaction involves PEP to pyruvate. It has such a large decrease in energy that it cannot be reversed so easily and requires different approach. In gluconeogenesis this occurs in 2 steps. Therefore a total of two high energy phosphate bonds are required to reverse this step.

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