14. What are the thermodynamic constraints on the formation of phosphoenolpyruvate from pyruvate and how are they overcome in gluconeogenesis? A. The ÎGÂ°Ë for the reverse of the glycolytic reaction for pyruvate kinase is +31 kJ/mol, which is overcome in gluconeogenesis by the carboxylation/decarboxylation reactions

 B. The ÎGÂ°Ë for the reverse of the glycolytic reaction for pyruvate kinase is -31 kJ/mol, which is overcome in gluconeogenesis by the carboxylation/decarboxylation reactions

 C. The ÎGÂ°Ë for the reverse of the glycolytic reaction for pyruvate kinase is -31 kJ/mol, which is overcome in gluconeogenesis by the futile cycle enzymes

 D. The ÎGÂ°Ë for the reverse of the glycolytic reaction for pyruvate kinase is â0.8 kJ/mol, which is overcome in gluconeogenesis by the futile cycle reactions

 E. The ÎGÂ°Ë for the reverse of the glycolytic reaction for pyruvate kinase is +0.8 kJ/mol, which is overcome in gluconeogenesis by the actions of pKa

 

15. Glycerol, lactate, and amino acids contribute carbon precursors in the formation of glucose; however, the path that glycerol takes is striking different from the other precursors. Explain how it differs? A. Glycerol is oxidized and enters gluconeogenesis as glyceraldehyde phosphate

 B. Glycerol enters gluconeogenesis as a breakdown product of triacylglycerols in the form of dihydroxyacetone phosphate

 C. Glycerol undergoes a reversible reduction/oxidation reaction to form phosphoenolpyruvate

 D. Glycerol is decarboxylated to acetyl CoA and enters gluconeogenesis as pyruvate

 E. Glycerol is first oxidized in a reaction requiring NAD+ and then phosphorylated in reversible reaction of glycolysis

 

20. Chemically, why is it necessary for citrate to undergo an isomerization to isocitrate prior to decarboxylation? A. Only when the alcohol is attached to C-2 can it block prolyl hydroxylase 2 activity, ensuring synthesis of glycolytic proteins

 B. The tertiary alcohol in citrate does not favor the oxidative carboxylation that occurs next; however, the secondary alcohol of isocitrate does

 C. Citrate induces a major structural rearrangement in aconitase leading to the creation of the binding site for the water molecule in the hydration step

 D. This conversion forms an unstable α-ketoacid, which drives the cycle forward 

 E. The aconitase reaction is a thermodynamically unfavored hydration reaction followed by a highly favored dehydration

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