reg of carb metabolism

• Carbohydrate metabolism


  Series of biochemical processes that ensure the body has a continuous supply of energy
• Key pathways in carbohydrate metabolism

  • Glycolysis
  • Gluconeogenesis
  • Glycogen synthesis
  • Glycogen degradation
• Glycolysis


  1. Breaks down glucose to pyruvate, producing ATP and NADH

  2. Occurs in the cytoplasm

  3. Key enzymes: Hexokinase, Phosphofructokinase-1 (PFK-1), Pyruvate Kinase
• Gluconeogenesis


  1. Synthesizes glucose from non-carbohydrate precursors like lactate, glycerol, and amino acids

  2. Mainly occurs in the liver and kidney cortex

  3. Key enzymes: Pyruvate Carboxylase, PEP Carboxykinase, Fructose-1,6-bisphosphatase (FBPase-1), Glucose-6-phosphatase
• Hexokinase


  • Converts glucose to glucose-6-phosphate (G6P)
  • High affinity for glucose
  • Inhibited by G6P (product inhibition)
• Glucokinase (Hexokinase IV)


  • Lower affinity for glucose, allowing it to function when glucose levels are high
  • Not inhibited by G6P, allowing continuous uptake and phosphorylation of glucose
  • Regulated by sequestration in the nucleus
• Phosphofructokinase-1 (PFK-1)


  • Allosterically activated by AMP, ADP, and fructose-2,6-bisphosphate (F2,6BP)
  • Allosterically inhibited by ATP and citrate
• Fructose-1,6-bisphosphatase (FBPase-1)


  • Allosterically inhibited by AMP and F2,6BP
  • Activated by citrate
• Pyruvate Kinase


  • Allosterically activated by F1,6BP
  • Allosterically inhibited by ATP, acetyl-CoA, and long-chain fatty acids
  • In the liver, inactivated by phosphorylation by protein kinase A (PKA) in response to glucagon signaling
• Glycogen Synthesis (Glycogenesis)


  1. Converts glucose to glycogen for storage

  2. Occurs in the liver and muscle

  3. Key enzymes: Glycogenin, UDP-Glucose Pyrophosphorylase, Glycogen Synthase, Branching Enzyme
• Glycogen Degradation (Glycogenolysis)


  1. Breaks down glycogen to release glucose

  2. Occurs in the liver and muscle

  3. Key enzymes: Glycogen Phosphorylase, Debranching Enzyme
• Glycogen Phosphorylase


  • Activated by phosphorylation and allosterically by AMP
  • Inhibited by dephosphorylation and allosterically by ATP and G6P
  • Hormonally regulated by glucagon and adrenaline via the cAMP/PKA pathway
• Glycogen Synthase


  • Activated by dephosphorylation and allosterically by G6P
  • Inhibited by phosphorylation by GSK3 and PKA
  • Hormonally regulated by insulin, which inhibits GSK3 and promotes the dephosphorylation and activation of glycogen synthase
• Insulin


  Promotes glycogen synthesis, increases glucose uptake, and inhibits gluconeogenesis
• Glucagon


  Promotes glycogenolysis and gluconeogenesis in the liver
• Adrenaline (Epinephrine)


  Stimulates glycogenolysis in liver and muscle
• Metabolic Integration and Compartmentalization

  • Different pathways are compartmentalized within cells to prevent futile cycles
  • Enzymes are organized in complexes to efficiently channel substrates through metabolic pathways
• Regulation of Carbohydrate Metabolism

  • Regulation by enzyme activity, substrate levels, energy change, and hormonal regulation
• Carbohydrate metabolism is tightly regulated to maintain energy homeostasis
• Glycolysis and gluconeogenesis are reciprocally regulated to prevent futile cycling
• Glycogen metabolism is controlled by a balance between synthesis and degradation, influenced by hormonal signals
• Enzyme activity, substrate levels, energy status, and compartmentalization all play roles in regulating metabolic flux