Carbs 2 Glucose Utilization

• Energy metabolism: chemical reactions that enable cells to store and use energy from nutrients
• Glycolysis: conversion of glucose to pyruvate
• Glucose=6 carbon atoms, pyruvate=3 carbon atoms
• Hexokinase: converts glucose to glucose-6-phosphate. Rate-limiting enzyme, traps glucose in the cell and activates it for metabolism
• Phosphofructokinase 1 (PFK1): converts F6P to F1,6BP. Rate limiting enzyme
• Pyruvate Kinase: converts phosphoenolpyruvate (PEP) to pyruvate in the final step of glycolysis
• Allosteric regulation: binds to enzymes to either increase or decrease the rate of reaction
• PFK1 is subject to allosteric regulation by metabolites that signal the energy level and hormonal status of the cell
• + regulators: AMP (low energy status), P, insulin
• neg. regulators: ATP, citrate, glucagon, and epinephrine
• Pyruvate kinase is positively activated by fructose 1,6 biphosphate and negatively activated by ATP
• RBC: pyruvate fate is pentose phosphate pathway or lactate
• Brain: pyruvate fate is acetyl CoA oxidation
• Adipocyte: pyruvate fate is acetyl CoA oxidation, or become a glycerol backbone
• Skeletal muscle: pyruvate fate is Acetyl CoA oxidation, lactate, glycogen, inter-muscular fatty acid synthesis
• Liver: pyruvate fate is acetyl CoA oxidation, palmitate, pyruvate, glycogen, pentose phosphate pathway, glucuronides,
• Fructose cannot be stored as glycogen because it enters the glycolytic pathway at a lower point
• Fructose is metabolized to form glyceraldehyde-3-phosphate
• Galactose: metabolized into glucose-1-phosphate for glycogen synthesis or gluce-6-phosphate for further metabolism
• Glycogen synthesis is highest when there is high glucose levels in the blood
• Glycogen synthase: is active when dephosphorylated, inactive when phosphorylated
• Protein phosphate 1 dephosphorylates glycogen synthase. This is regulated by insulin, glucose-6-phosphate, and glucose
• Glycogen synthase kinase 3 phosphorylates glycogen synthase. This is regulated by glucagon and epinephrine
• Glycogenolysis: glycogen breakdown
• Glycogen phosphorylase: catalyzes the break of alpha 1,4 glycosidic bonds. Yields glucose-1-P and a shortened glycogen polymer
• Debranching enzymes are required to break the alpha 1,6 linkages of branch points
• Gluconeogenesis: glucose production, pyruvate to glucose. in liver and kidney