Question

To enhance gluconeogenesis using acetyl CoA from the oxidation of fatty acids, the normal TCA cycle is turned off by phosphorylation of ___ and the glyoxylate cycle is turned on, instead. This cycle uses two acetyl-CoA to produce one ___ , which is also substrate for gluconeogenesis.

Select one:

a. isocitrate dehydrogenase ; oxaloacetate

b. isocitrate lyase ; citrate

c. isocitrate dehydrogenase ; citrate

d. isocitrate lyase ; oxaloacetate

e. None of these

Answer 1

Gluconeogenesis is a metabolic pathway which is almost reverse of the glycolysis process and usually takes place in the liver and kidney. This process usually refers to the formation of glucose from non carbohydrate precursors which includes lactate, glycerol, glucogenic amino acids and propionyl CoA.  

Oxidation of fatty acids elevates the concentrations of ATP, acetyl - CoA and citrate which are important effectors during gluconeogenesis (John W. Pelley, 2012) and help in the following ways:

• Acetyl - CoA activates pyruvate carboxylase which converts pyruvate to oxaloacetate for use in gluconeogenic pathway.
• Inhibition of pyruvate dehydrogenase by acetyl - CoA increases switching of pyruvate towards oxaloacetate.
• Cytrate allosterically inhibits phosphofructokinase 1, preventing a futile cycle with F1,6-BP (BisPhosphatase)
• Increased ATP (Adenosine Tri Phosphate) concentration inhibit glycolysis while provoding energy for gluconeogenesis.