Glucogenesis

• What is the process of synthesizing glucose from noncarbohydrate precursors called?

  Gluconeogenesis

  
• Name one noncarbohydrate precursor from which glucose can be synthesized.

  Pyruvate

  
• What is another noncarbohydrate precursor for glucose synthesis besides pyruvate?

  The carbon skeletons of some amino acids

  
• What is the third noncarbohydrate precursor mentioned for glucose synthesis?

  Glycerol

  
• How is pyruvate formed from muscle-derived lactate in the liver?

  By lactate dehydrogenase
• What are the main steps in gluconeogenesis from pyruvate?

  1. Pyruvate is converted to oxaloacetate by pyruvate carboxylase.
  2. Oxaloacetate is converted to phosphoenolpyruvate by phosphoenolpyruvate carboxykinase.
  3. Phosphoenolpyruvate is metabolized in reverse glycolysis until fructose 1,6-bisphosphate.
  4. Fructose 1,6-bisphosphate is converted to glucose.

  
• Where does gluconeogenesis primarily occur?

  The liver
• Why is gluconeogenesis especially important during fasting?

  Glucose is the primary fuel for the brain
• What is the first enzyme required in the conversion of pyruvate to phosphoenolpyruvate?

  Pyruvate carboxylase

  
• What cofactor is required by pyruvate carboxylase?

  Biotin

  
• How many stages occur in the formation of oxaloacetate by pyruvate carboxylase?

  Three stages

  
• What happens to oxaloacetate after it is formed in the mitochondria?

  It is reduced to malate and transported

  
• What is the role of phosphoenolpyruvate carboxykinase in gluconeogenesis?

  It converts oxaloacetate into phosphoenolpyruvate

  
• What is the net reaction after Steps 1 and 2 of gluconeogenesis?

  Phosphoenolpyruvate is metabolized in reverse glycolysis

  
• What is the function of fructose 1,6-bisphosphatase in gluconeogenesis?

  It is an allosteric enzyme

  
• Where does glucose 6-phosphate get transported for conversion to glucose?

  Into the lumen of the endoplasmic reticulum

  
• What is the final step in gluconeogenesis?

  Generation of free glucose
• What is the significance of glucose 6-phosphatase in gluconeogenesis?

  It is an important control point

  
• What prevents glycolysis from simply running in reverse to synthesize glucose?

  Irreversible steps in glycolysis
• What regulates the balance between glycolysis and gluconeogenesis in the liver?

  • Blood-glucose concentration
  • Reciprocal regulation
  • Fructose 2,6-bisphosphate as a key regulator

  
• How does fructose 2,6-bisphosphate affect glucose metabolism in the liver?

  It stimulates phosphofructokinase and inhibits fructose 1,6-bisphosphatase

  
• What is a bifunctional enzyme in the context of fructose 2,6-bisphosphate regulation?

  It has both kinase and phosphatase activities

  
• What triggers the release of glucagon from the pancreas?

  Low blood glucose levels
• What is the role of protein kinase in the regulation of fructose 2,6-bisphosphate?

  It phosphorylates the PFK2 domain of the enzyme

  
• What happens to glucose levels during fasting if glucose 6-phosphatase is inactive?

  Glucose levels would drop dangerously low

  
• What is the irreversible step in the formation of acetyl CoA from pyruvate?

  Formation of acetyl CoA is irreversible

  
• What are the two possible fates of acetyl CoA?

  Metabolism by the citric acid cycle or fatty acids

  
• What are the steps involved in the synthesis of acetyl CoA from pyruvate?

  1. Decarboxylation
  2. Oxidation
  3. Transfer to CoA

  
• What is the role of lipoamide in the pyruvate dehydrogenase complex?

  It allows rapid movement of substrates

  
• How many enzymes are involved in the synthesis of acetyl CoA from pyruvate?

  Three enzymes

  
• What is the significance of the structural integration of the pyruvate dehydrogenase complex?

  It allows efficient substrate transfer
• What is the fate of acetyl CoA in animal cells?

  Metabolism by the citric acid cycle

  
• What is the process that forms acetyl CoA from pyruvate?

  Irreversible conversion in animal cells

  
• How many enzymes are required for the synthesis of acetyl CoA from pyruvate?

  Three enzymes

  
• What are the three chemical steps in synthesizing acetyl CoA from pyruvate?

  Decarboxylation, oxidation, transfer to CoA

  
• What coenzyme is formed by attaching lipoic acid to lysine?

  Lipoamide
• What is the role of lipoamide in the pyruvate dehydrogenase complex?

  Allows movement between different sites

  
• How do the three enzymes of the pyruvate dehydrogenase complex interact?

  They are structurally integrated for substrate movement
• How is the pyruvate dehydrogenase complex regulated by covalent modification?

  Phosphorylation deactivates enzyme E1

  
• What activates the kinase associated with the pyruvate dehydrogenase complex?

  Glucagon when glucose is low