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CARBOHYDRATE DIGESTION & METABOLISM. Definition. Metabolism (from Greek : μεταβολή " metabolē ", "change" or Greek : μεταβολισμός metabolismos , " outthrow ") is the set of chemical reactions that happen in the cells of living organisms to sustain life. - PowerPoint PPT Presentation



CARBOHYDRATE DIGESTION & METABOLISMDefinitionMetabolism (from Greek: "metabol", "change" or Greek: metabolismos, "outthrow") is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories. Catabolism breaks down organic matter, for example to harvest energy in cellular respiration. Anabolism uses energy to construct components of cells such as proteins and nucleic acids.Chemical ReactionThe chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, by a sequence of enzymes. Enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy and will not occur by themselves, by coupling them to spontaneous reactions that release energy. As enzymes act as catalysts they allow these reactions to proceed quickly and efficiently. Enzymes also allow the regulation of metabolic pathways in response to changes in the cell's environment or signals from other cells.

Selective reactionThe metabolism of an organism determines which substances it will find nutritious and which it will find poisonous. For example, some prokaryotes use hydrogen sulfide as a nutrient, yet this gas is poisonous to animals. The speed of metabolism, the metabolic rate, influences how much food an organism will require, and also affects how it is able to obtain that food.CARBOHYDRATE DIGESTIONAMYLUM digestion by amylase enzyme

Disaccharides digestion

Glucose is the most important carbohydrateGlucose is the major metabolic fuel of mammals, except ruminants Monosaccharide from diet : - Glucose - Fructose - GalactoseFructose and Galactose glucose at the liver

Galactose Metabolism

Fructose Metabolism

Blood glucose carbohydrate metabolism exist are : 1. Glycolisis 2. Glycogenesis 3. HMP Shunt 4. Oxidation of Pyruvate 5. Krebs Cycle 6. Change to lipids Fasting blood glucose carbohydrate metabolism : 1. Glycogenolisis 2. Gluconeogenesis GLYCOLISISGlycolisis oxidation of glucose energyIt can function either aerobically or anaerobically

pyruvate lactateOccurs in the cytosol of all cellAEROBICALLY GLYCOLYSIS : Pyruvate Mitochondria oxidized to Asetil CoA Krebs Cycle CO2 + H2O + ATPGlycolisis

Most of the reaction of glycolysis are reversible, except of three reaction : 1. Glucose Glucose-6-phosphate, catalyzed by Hexokinase / GlucokinaseHexokinase : - Inhibited allosterically by its product glucose-6-p - Has a high affinity for its substrate glucose - available at all cell, except liver and islet cell Glucokinase : - available at liver and islet cell - in the liver to remove glucose from the blood after meal 2. Fructose-6-P Fructose-1,6-biP - catalyzed by Phosphofructokinase enzyme - Irreversible - Rate limiting enzyme in glycolysis 3. Phosphoenolpyruvate Enol Pyruvate - Catalyzed by Pyruvate kinase enzymeOxidation of 1 mol glucose 8 mol ATP and 2 mol PyruvateANAEROBICALLY GLYCOLYSIS : - The reoxidation of NADH through the respiratory chain to oxygen is prevented - Pyruvate is reduced by the NADH to lactate, by Lactate dehidrogenase enzyme Lactate dehydrogenasePyruvate + NADH + H+ Lactate + NAD+

- Oxidation 1 mol glucose via anaerobically glycolysis 2 mol ATP

ANAEROBICALLY GLYCOLYSIS : Respiratory chain is absence

Reoxidation of NADH NAD+ via Respiratory chain is inhibited

Reoxidation of NADH via lactate formation allows glycolysis to proceed in the absence of oxygen by regenerating sufficient NAD+

GLYCOLYSIS IN ERYTHROCYTEErythrocyte lack mitochondria respiratory chain and Krebs cycle are absenceAlways terminates in lactateIn mammals the reaction catalyzed by phosphoglycerate kinase may be bypassed by a process that catalyzed Biphosphoglycerate muta- seIts does serve to provide 2,3-biphosphoglycerate bind to hemoglobin decreasing its affinity for oxygen oxygen readily available to tissuesGLYCOLYSIS IN ERYTHROCYTE

OXIDATION OF PYRUVATEOccur in mitochondriaOxidation of 1 mol Pyruvate 1 mol Asetyl-CoA + 3 mol ATPCH3COCOOH + HSCoA + NAD+ CH3CO-SCoA + NADH (Pyruvate) (Asetyl-CoA)Catalyzed by Pyruvate dehydrogenase enzymeThis enzyme need CoA as coenzymeIn Thiamin deficiency, oxydation of pyruvate is impaired lactic and pyruvic acid


GLYCOGENESISSynthesis of Glycogen from glucoseOccurs mainly in muscle and liver cellThe reaction : Glucose Glucose-6-P Hexokinase / Glucokinase Glucose-6-P Glucose-1-P PhosphoglucomutaseGlucose-1-P + UTP UDPG + Pyrophosphate UDPG PyrophosphorylaseGLYCOGENESISGlycogen synthase catalyzes the formation of -1,4-glucosidic linkage in glycogen Branching enzyme catalyzes the formation of -1,6-glucosidic linkage in glycogen

Finally the branches grow by further additions of 1 4-gucosyl units and further branching (like tree!)SYNTHESIS OF GLYCOGEN



Glycogenesis Glycogenolysis

GLYCOGENOLYSISThe breakdown of glycogenGlycogen phosphorilase catalyzes cleavage of the 14 linkages of glycogen to yield glucose-1-phosphate(14)(14) glucan transferase transfer a trisaccharides unit from one branch to the otherDebranching enzyme hydrolysis of the 16 linkagesThe combined action of these enzyme leads to the complete breakdown of glycogen.GLYCOGENOLYSIS PhosphoglucomutaseGlucose-1-P Glucose-6-P Glucose-6-phosphataseGlucose-6-P GlucoseGlucose-6-phosphatase enzyme a spesific enzyme in liver and kidney, but not in muscle Glycogenolysis in liver yielding glucose export to blood to increase the blood glu- cose concentrationIn muscle glucose-6-P glycolysisGLUCONEOGENESISPathways that responsible for converting noncarbohydrate precursors to glucose or glycogenIn mammals occurs in liver and kidneyMajor substrate : 1. Lactic acid from muscle, erythrocyte 2. Glycerol from TG hydrolysis 3.Glucogenic amino acid 4. Propionic acid in ruminantGluconeogenesis meets the needs of the body for glucose when carbohydrate is not available from the diet or from glycogenolysisA supply of glucose is necessary especially for nervous system and erythrocytes.The enzymes : 1. Pyruvate carboxylase 2. Phosphoenolpyruvate karboxikinase 3. Fructose 1,6-biphosphatase 4. Glucose-6-phosphataseGLUCONEOGENESIS




HMP SHUNT/HEXOSE MONO PHOSPHATE SHUNT = PENTOSE PHOSPHATE PATHWAYAn alternative route for the metabolism of glucoseIt does not generate ATP but has two major function : 1. The formation of NADPH synthesis of fatty acid and steroids 2. The synthesis of ribose nucleotide and nucleic acid formationHMP SHUNTActive in : liver, adipose tissue, adrenal cortex, thyroid, erythrocytes, testis and lactating mammary glandIts activity is low in muscleIn erythrocytes : HMP Shunt provides NADPH for the reduction of oxidized glutathione by glutathione reductase reduced glutathi- one removes H2O2 glutathione peroxidase HMP SHUNT Glutathione reductaseG-S-S-G 2-G-SH(oxidized glutathione) (reduced glutathione) Glutathione peroxidase2-G-SH + H2O2 G-S-S-G + 2H2OThis reaction is important accumulation of H2O2 may decrease the life span of the erythrocyte damage to the membrane cell hemolysisHMP SHUNT

BLOOD GLUCOSEBlood glucose is derived from the : 1. Diet the digestible dietary carbohy- drate yield glucose blood 2. Gluconeogenesis 3. Glycogenolysis in liverInsulin play a central role in regulating blood glucose blood glucoseGlucagon blood glucoseGrowth hormone inhibit insulin activityEpinefrine stress blood glucose