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Metabolic Regulation 2 quiz

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  • What is the commitment step of glycolysis catalyzed by phosphofructokinase 1 (PFK1)?
    The commitment step is the phosphorylation of fructose 6-phosphate to fructose 1,6-bisphosphate, committing the molecule to glycolysis.
  • Which molecules allosterically inhibit PFK1 activity?
    ATP and citrate both allosterically inhibit PFK1, signaling high energy or biosynthetic precursor abundance.
  • How do AMP and ADP affect PFK1 activity?
    AMP and ADP stimulate PFK1 activity, indicating low cellular energy and promoting glycolysis.
  • What is the most important allosteric activator of PFK1?
    Fructose 2,6-bisphosphate is the most important allosteric activator of PFK1, even at very low concentrations.
  • How does fructose 2,6-bisphosphate affect gluconeogenesis?
    Fructose 2,6-bisphosphate inhibits fructose 1,6-bisphosphatase, thereby inhibiting gluconeogenesis.
  • What dual effect does AMP have on glycolysis and gluconeogenesis?
    AMP stimulates PFK1 (activating glycolysis) and inhibits fructose 1,6-bisphosphatase (inhibiting gluconeogenesis).
  • Which enzyme produces fructose 2,6-bisphosphate?
    Phosphofructokinase 2 (PFK2) produces fructose 2,6-bisphosphate.
  • How does insulin regulate PFK2 activity?
    Insulin stimulates the dephosphorylation and activation of PFK2, increasing fructose 2,6-bisphosphate production.
  • What effect does glucagon have on PFK2?
    Glucagon causes phosphorylation and inactivation of PFK2, reducing fructose 2,6-bisphosphate levels.
  • How are PFK2 and fructose 2,6-bisphosphatase related structurally?
    PFK2 and fructose 2,6-bisphosphatase are linked together in a bifunctional enzyme, with one active when the other is inactive.
  • What molecule from the pentose phosphate pathway stimulates protein phosphatase to activate PFK2?
    Xylulose-5-phosphate (X5P) stimulates protein phosphatase, which activates PFK2.
  • How is pyruvate kinase regulated in the liver by glucagon?
    Glucagon activates protein kinase A, which phosphorylates and inactivates pyruvate kinase in the liver, reducing glycolysis.
  • Which molecules inhibit pyruvate kinase activity?
    ATP, acetyl CoA, long-chain fatty acids, and alanine all inhibit pyruvate kinase.
  • What is the feed-forward activator of pyruvate kinase?
    Fructose 1,6-bisphosphate acts as a feed-forward activator of pyruvate kinase.
  • Which enzyme initiates gluconeogenesis and what activates it?
    Pyruvate carboxylase initiates gluconeogenesis and is activated by acetyl CoA.