NFNF1613 Carbohydrate Metabolism I 2024-2025 PDF

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UKM

2024

NFNF

Mohd Kaisan Mahadi

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carbohydrate metabolism biochemistry glucose human biology

Summary

This document is lecture notes for the course "NFNF1613 Biokimia Manusia." It covers carbohydrate metabolism, including glycolysis, pentose phosphate pathway, glycogenolysis, gluconeogenesis, glycogenesis, cellular respiration and the citric acid cycle/Krebs cycle, as well as fates of pyruvate.

Full Transcript

NFNF1613 BIOKIMIA MANUSIA Dr. Mohd Kaisan Mahadi Fakulti Farmasi, UKM [email protected] Carbohydrate Metabolism I Overview Digestion Absorption Catabolism processes glycolysis, pentose-phosphate pathway, glycogenolysis Anabolism processes...

NFNF1613 BIOKIMIA MANUSIA Dr. Mohd Kaisan Mahadi Fakulti Farmasi, UKM [email protected] Carbohydrate Metabolism I Overview Digestion Absorption Catabolism processes glycolysis, pentose-phosphate pathway, glycogenolysis Anabolism processes gluconeogenesis, glycogenesis Cellular respiration Citric acid cycle/TCA cycle/Krebs cycle Why metabolised? The need to generate energy from the metabolic processes Precursors for subsequent metabolic processes Polysaccharide digestion Starts in the mouth Starch (amylose and amylopectins) broken down by α-amylase α-amylase produced by salivary and pancreatic glands Hydrolyzes internal α-1,4 bonds between glucosyl residues at random intervals in the polysaccharide chain Inactivated in the stomach due to high acidity environment Brush border enzymes Present on the membrane of microvilli structures on absorptive cells in intestine Glycosidases Convert disaccharides/oligosaccharides to monosaccharides 4 main types : 1. Glucoamylase 2. Sucrose-isomaltase complex 3. Trehalase 4. β-glycosidase complex (lactase-glucosylceramidase) Indigestible carbohydrates Proceed to the colon Metabolized by colonic bacteria Produce gases, short- chain fatty acids, lactate Dietary fibres Absorption Monosaccharides absorbed across intestinal epithelial cells à bloodstream à tissues à cells Mode of glucose absorption: Facilitated diffusion transport Na+-dependent active transport Na+-dependent glucose transporters Na+-dependent glucose transporters SGLT protein family Harada 2012, Journal of Diabetes Investigation Vol 3 Issue 4 Aug 2012 Facilitative glucose transporters Movement of glucose from high to low concentration No energy expenditure Facilitative glucose transporters GLUT protein family Glycolysis Watch this video on glycolysis Glycolysis Glucokinase Glycolysis is the process in which glucose is broken down to produce energy. It produces two molecules of pyruvate, ATP, NADH and water. The process takes place in the cytoplasm of a cell and does not require oxygen. It occurs in both aerobic and anaerobic organisms. ** glucokinase in the liver, hexokinase in any other cells Net Reaction Fates of pyruvate Aerobic condition : pyruvate enters Citric Acid/Krebs cyle (complete oxidation of glucose) Anaerobic condition : pyruvate à lactate (fermentation) Insufficient glucose stores (eg. long fasting; glycogen depletion) : pyruvate à glucose (gluconeogenesis) Cellular respiration A process where cells consume O2 and produce CO2 3 major stages Oxidative Decarboxylation TCA/Krebs Cycle Goal: Generate NADH and FADH2 Points to remember: Rate limiting step – isocitrate dehydrogenase. Allosterically activated by ADP and NADH. ADP stimulates the TCA cycle when there is lack of ATP, hence producing NADH and FADH2. When NADH are exactly produced (I, K, M) When FADH2 are produced (Succinate - Fumrate) End products: 1. NADH 2. FADH2 3. ATP or GTP Oxaloacetate (to be recycled) Nett ATP production Large amount of ATP production contributed by the NADH and FADH2 Importance of Citric Acid cycle Amphibolic pathway à play role for both catabolic and anabolic reactions Catabolism of carbohydrates, fatty acids and amino acids Anabolic for: 1. α-ketoglutarate & oxaloacetate à precursors to build amino acids 2. Oxaloacetate à intermediate required to produce glucose in gluconeogenesis 3. Succinyl CoA à intermediate in synthesis of porphyrin ring of heme groups (O2 carrier in hemoglobin) Lactic Acid Fermentation Occurs in tissues with insufficient oxygen cell types which do not contain mitochondria (eg. erythrocytes) The need to re-oxidise NADH to NAD+ à if not, glycolysis will stop Gluconeogenesis Gluconeogenesis Formation of new glucose molecules from non- carbohydrate precursors Liver & Kidney Due to hypoglycemia/survival of the brain cells. Reciprocal process to glycolysis Gluconeogenesis Thank you

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