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Introduction to glucose metabolism

Introduction to glucose metabolism. Overview of glucose metabolism. Objectives. Recognizing the critical importance of glucose as the main carbohydrate of blood & main fuel of human cells . Recognizing glucose transport into cells

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Introduction to glucose metabolism

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  1. Introduction to glucose metabolism

  2. Overview of glucose metabolism

  3. Objectives • Recognizing the critical importance of glucose as the main carbohydrate of blood & main fuel of human cells. • Recognizing glucose transport into cells • Recalling the sources of blood glucose in feed & fasting states. • Understand the basic concepts & directions (pathways) of metabolism.

  4. General importance of carbohydrates in human body 1- Provide energy through metabolism pathways and cycles 2- Store energy in the form of: starch (in plants) glycogen (in animals and humans) 3- Supply carbonfor synthesis of other compounds. 4- Form structural components in cells and tissues.

  5. Critical importance of glucose A constant source of GLUCOSE is an absolute requirement for human life as it is: 1- Preferred energy of the brain 2- Required energy source for cells with no or few mitochondria (as RBCs) 3- Essential source of energy for exercising muscles (substrate for anerobic glycolysis)

  6. Glucose transport into cells 1- Na+-independent facilitated diffusion transport: • Transport occurs with concentrationgradient • Norequire for energy (i.e. ATP) • It is conducted by a group of at least 14 glucose transporters (GLUT-1 to 14)

  7. Glucose transport into cells (cont.) GLUT-1 is abundant in RBCs & Brain GLUT-2 is found in liver, kidney & b-cells of the pancreas Function in both directions (from blood to cells & from cells to blood) GLUT-3 primary glucose transporter in neurons GLUT-4 is abundant in adipose tissue & skeletal muscles Number is increased by insulin GLUT-5is the primary transporter of fructose GLUT-7 is expressed in gluconeogenic tissue (as the liver) mediates glucose flux across ER membrane

  8. Glucose transporters (GLUT)

  9. Glucose transport into cells (cont.) 2- Na+-monosaccharide cotransportersystem • Glucose is transported against a concentration gradient from low glucose concentrations outside the cell to higher concentrations within the cell • Energy-requiring process • It is a carrier-mediated process in which the movement of glucose is coupled to the concentration gradient of Na+, which is transported into the cell at the same time • This type of transport occurs in the epithelial cells of the intestine & renal tubules

  10. GLUCOSE TRANSPORT & INSULIN

  11. Sources of Glucose to human Body Glucose can be obtained from three primary sources: Carbohydrate in Diet: • Carbohydrates are sources for glucose of the body after meals. • Excess glucose is stored in the form of glycogen in liver & skeletal muscles. Glycogen degradation (Glycogenlysis): • Glycogen (synthesized from glucose molecules) is stored in liver & skeletal muscles. • In cases of fasting, liver glycogen is degraded to yield glucose for blood. • In cases of muscular exercise, muscle glycogen is degraded to secure glucose for muscles as a source of energy. Gluconeogenesis (Glucose Synthesis): • It is the synthesis of glucose from non carbohydrate sources (as some amino acids) • It occurs in prolonged fasting

  12. Sources of glucose of carbohydrate diet 1-Free Monosaccharides: mainly glucose & fructose Fructose is converted into glucose in liver 2-Disaccharides: -Sucrose (glucose & fructose) - Lactose (glucose & galactose) - Maltose (glucose & glucose) They are digested into monosaccharides (glucose, fructose & galactose) in the intestine. Fructose & galactose are converted into glucose in the liver 3-Polysaccharides: - Starch(plant source e.g. rice, potato, flour) - Glycogen(animal source) They are digested into glucose in the GIT

  13. Metabolic pathways of glucose Hexoses fructose & galactose Glycogenolysis Glycogenesis GLUCOSE Gluconeogenesis Hexoses fructose & galactose HMP/PPP Glycolysis Krebs cycle PRODUCTION Utilization

  14. Pathways of glucose utilization 1- Catabolic pathways: 1- For providing energy (ATP): Glycolysis Anaerobic Glycolysis: end product is lactate Aerobic Glycolysis: end product is pyruvate 2- For providing synthetic products: Hexose monophosphate pathway (Produces NADPH & Ribose 5-Phosphate) 2- Synthetic pathways: Glycogen synthesis

  15. GLUCOSE Pyruvate Acetyl CoA Citric Acid Cycle NADH & FADH2 Electron transport chain (flow of electrons) Formation of ATP (oxidative phosphorylation) HEXOSE MONOPHOSPHATE PATHWAY GLYCOGEN SYNTHESIS Ribose-5 Phosphate Glycogen NADPH GLYCOLYSIS No Oxygen No Mitochondria OR BOTH Utilization of Glucose Lactate Oxygen & Mitochondria

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