Glucose Metabolism Lecture Notes PDF

Introduction to 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 Recalling the sources of blood glucose in feed & fasting states. Unde...

Introduction to 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 Recalling the sources of blood glucose in feed & fasting states. Understand the basic concepts & directions (pathways) of metabolism. 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 (RBCs) 3- Essential source of energy for exercising muscles (anaerobic glycolysis) Glucose transport into cells 1- Na+-independent facilitated diffusion transport (GLUT): Transport occurs with concentration gradient No require for energy (i.e. ATP) It is conducted by a group of at least 14 glucose transporters (GLUT-1 to 14) 2- Na+-monosaccharide cotransporter system (SGLUT) Glucose is transported against a concentration gradient from low glucose concentrations outside the cell to higher concentrations within the cell Energy-requiring process The movement of glucose is coupled to the concentration gradient of Na+, which is transported into the cell at the same time ( Co- transporter). This type of transport occurs in the epithelial cells of the intestine & renal tubules Sources of blood Glucose in human Body Glucose can be obtained from three primary sources: 1- 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. 2- Glycogen degradation (Glycogenlysis): 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. 3- Gluconeogenesis (Glucose Synthesis): It is the synthesis of glucose from non carbohydrate sources (as some amino acids). It occurs in prolonged fasting  Sources of glucose in 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 by disacchridases (sucrase, lactase and maltase) into glucose, fructose & galactose in 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 by amylase into maltose then by maltase into glucose in the GIT Fates of blood glucose 1- Catabolic pathways: 1- For providing energy (ATP): Glycolysis then kreb’s 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 lipogenesis protein synthesis other carbohydrates  HEXOSE MONOPHOSPHATE GLYCOGEN PATHWAY SYNTHESIS Ribose-5 Phosphate GLUCOSE Glycogen NADPH GLYCOLYSIS No Oxygen No Utilizati Mitochondria OR BOTH Lactate Pyruvate on Oxygen & Mitochondria of Acetyl CoA Citric Acid Cycle Glucose NADH & FADH2 Electron transport chain (flow of electrons) Formation of ATP (oxidative phosphorylation)