Glycolysis Regulation
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Questions and Answers

Hexokinase is regulated positively by Glucose-6-P.

True

Fructose-2,6-bisphosphate enhances the activity of Phosphofructokinase-1.

True

ATP acts as a positive regulator of the enzyme Pyruvate kinase.

False

Fructose-6-P is converted to Fructose-1,6-BP by the enzyme Phosphoglycerate kinase.

<p>False</p> Signup and view all the answers

Alanine acts as a positive regulator for the enzyme Pyruvate kinase.

<p>False</p> Signup and view all the answers

Hexokinase is negatively regulated by Fructose-6-P.

<p>False</p> Signup and view all the answers

Fructose-1,6-bisphosphate is a regulatory molecule for Pyruvate kinase.

<p>True</p> Signup and view all the answers

Citrate functions as a positive regulator in the glycolysis pathway.

<p>False</p> Signup and view all the answers

Pyruvate kinase is irreversible in the glycolysis process.

<p>True</p> Signup and view all the answers

AMP acts as a negative regulator for Phosphofructokinase-1.

<p>False</p> Signup and view all the answers

ATP negatively regulates Phosphofructokinase-1.

<p>True</p> Signup and view all the answers

Pyruvate kinase is positively regulated by Glucagon.

<p>False</p> Signup and view all the answers

Fructose-1,6-bisphosphate is a positive regulator for Pyruvate kinase.

<p>True</p> Signup and view all the answers

The enzyme Hexokinase is regulated by the product Glucose-6-P.

<p>True</p> Signup and view all the answers

Citrate acts as a positive regulator in the glycolysis pathway.

<p>False</p> Signup and view all the answers

Fructose-6-P is converted to Fructose-1,6-BP by the enzyme Phosphofructokinase-1.

<p>True</p> Signup and view all the answers

Citrate serves as a negative regulator for Phosphofructokinase-1 in glycolysis.

<p>True</p> Signup and view all the answers

The enzyme Pyruvate kinase is positively regulated by Fructose-1,6-bisphosphate.

<p>True</p> Signup and view all the answers

AMP negatively regulates Phosphofructokinase-1.

<p>False</p> Signup and view all the answers

Glucagon acts as a positive regulator for the enzyme Pyruvate kinase.

<p>False</p> Signup and view all the answers

Study Notes

Glycolysis Regulation

  • Hexokinase/Glucokinase is inhibited by its product Glucose-6-Phosphate and by Fructose-6-Phosphate.
  • Phosphofructokinase-1 (PFK-1) is the rate-limiting step of glycolysis:
    • PFK-1 is activated by Fructose-2,6-bisphosphate, AMP, and high levels of ADP while it is inhibited by ATP, citrate, and low levels of ADP.
  • Phosphoglycerate kinase is reversible meaning it can operate in both directions of the reaction.
  • Pyruvate kinase is the last step in glycolysis and is irreversible:
    • It is activated by Fructose-1,6-bisphosphate which is a product of the previous step.
    • It is inhibited by Glucagon, Alanine, and low levels of ATP.

Glycolysis Regulation

  • Hexokinase/Glucokinase catalyzes the first step of glycolysis, converting glucose to glucose-6-phosphate.
    • Regulation is allosterically inhibited by glucose-6-phosphate.
    • Glucokinase in the liver is also regulated by fructose-6-phosphate.
  • The second step of glycolysis, where fructose-6-phosphate is converted to fructose-1,6-bisphosphate, is catalyzed by Phosphofructokinase-1 (PFK-1).
    • This is the rate-limiting step of glycolysis.
    • Regulation is complex, involving several factors:
      • Fructose-2,6-bisphosphate: Stimulates PFK-1 activity.
      • AMP: Stimulates PFK-1 activity, indicating low energy levels.
      • Citrate: Inhibits PFK-1 activity, indicating high energy levels.
      • ATP: Inhibits PFK-1 activity, indicating high energy levels.
  • Phosphoglycerate kinase catalyzes the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate in a reversible reaction.
  • Pyruvate kinase, in the final step, converts phosphoenolpyruvate to pyruvate in an irreversible reaction.
    • Regulation is influenced by various factors:
      • Fructose-1,6-bisphosphate: Stimulates pyruvate kinase activity.
      • Glucagon: Inhibits pyruvate kinase activity, promoting gluconeogenesis.
      • Alanine: Inhibits pyruvate kinase activity.
      • ATP: Inhibits pyruvate kinase activity, indicating high energy levels.

Glycolysis Regulation

  • Hexokinase/Glucokinase catalyzes the first step in glycolysis, the phosphorylation of glucose to glucose-6-phosphate
    • Regulation: Glucose-6-phosphate is an allosteric inhibitor of hexokinase, while fructose-6-phosphate inhibits glucokinase
  • Phosphofructokinase-1 (PFK-1) is the rate-limiting enzyme in glycolysis, catalyzing the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate
    • Regulation:
      • Fructose-2,6-bisphosphate activates PFK-1, promoting glycolysis
      • AMP activates PFK-1, indicating low energy levels
      • Citrate inhibits PFK-1, signaling high energy levels
      • Low ATP increases the activity of PFK-1
  • Phosphoglycerate Kinase catalyzes the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate, generating ATP
    • Regulation: Reversible, meaning it can work in both directions based on substrate availability
  • Pyruvate Kinase catalyzes the irreversible conversion of phosphoenolpyruvate to pyruvate, generating ATP
    • Regulation:
      • Fructose-1,6-bisphosphate activates pyruvate kinase, a feed-forward mechanism to speed up glycolysis
      • Glucagon, a hormone released during low blood sugar, inhibits pyruvate kinase
      • Alanine inhibits pyruvate kinase, reflecting high amino acid levels
      • Low ATP increases the activity of pyruvate kinase

Hexokinase / Glucokinase:

  • Hexokinase: All tissues (except liver), low Km (high affinity), high Vmax, inhibited by glucose-6-phosphate
  • Glucokinase: Liver, high Km (low affinity), low Vmax, not inhibited by glucose-6-phosphate, activated by fructose-6-phosphate
  • Both catalyze phosphorylation of glucose to glucose-6-phosphate
  • Regulation: Product inhibition by glucose-6-phosphate for hexokinase but not for glucokinase

Phosphofructokinase-1 (PFK-1):

  • Catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate (committed step of glycolysis)
  • Rate-limiting step: Controls the overall flux of glycolysis
  • Regulation:
    • Positive regulators: Fructose-2,6-bisphosphate (most potent activator), AMP (indicates low energy status)
    • Negative regulators: Citrate (indicate high energy status), ATP (high concentration indicates high energy status)

Phosphoglycerate Kinase:

  • Catalyzes the phosphorylation of 1,3-bisphosphoglycerate to 3-phosphoglycerate
  • Reversible reaction
  • Regulation: Not directly regulated

Pyruvate Kinase:

  • Catalyzes the conversion of phosphoenolpyruvate to pyruvate, which is the final step of glycolysis
  • Irreversible reaction
  • Regulation:
    • Positive regulators: Fructose-1,6-bisphosphate (feed-forward activation)
    • Negative regulators: Glucagon, alanine, low ATP levels (indicate high energy status)

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Description

This quiz focuses on the regulation of glycolysis, highlighting key enzymes such as Hexokinase, Phosphofructokinase-1, and Pyruvate kinase. Understand the mechanisms behind their activation and inhibition by various metabolites. Test your knowledge on this crucial metabolic pathway!

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