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CARBOHYDRATES

CARBOHYDRATES. Mrs. Chaitali Maitra Assistant Professor Dept. of Biochemistry PCMS&RC. TO MY STUDENTS HERE I HAVE TRIED TO SIMPLIFY THE HUGE SUBJECT WITH ANIMATIONS, DIAGRAMS, FLOW CHARTS & RELEVENT MCQs. DIFFERENT TEXT BOOKS AND REFERENCE BOOKS HAVE BEEN USED FOR

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CARBOHYDRATES

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  1. CARBOHYDRATES Mrs. Chaitali Maitra Assistant Professor Dept. of Biochemistry PCMS&RC

  2. TO MY STUDENTS HERE I HAVE TRIED TO SIMPLIFY THE HUGE SUBJECT WITH ANIMATIONS, DIAGRAMS, FLOW CHARTS & RELEVENT MCQs. DIFFERENT TEXT BOOKS AND REFERENCE BOOKS HAVE BEEN USED FOR PREPARING THE CONTENTS. REMEMBERTHESE SLIDES ARE NOT THE SUBSTITUTE OF YOUR TEXT BOOKS ANIMATIONS AND DIAGRAMS ARE COLLECTED FROM DIFFERENT WEBSITE SOLELY FOR EDUCATION PURPOSE.

  3. CARBOHYDRATES ARE ALDEHYDE OR KETONE DERIVATIVES OF POLYHYDRIC ALCOHOLS ;CLASSIFIED AS MONO,DI,OLIGO &POLY. 1.Monosaccharides The monosaccharide commonly found in humans are classified according to the number of carbons they contain in their backbone structures. Classifications ALDOSES KETOSES

  4. GLUCOSE Straight chain Haworth projection Hemiacetal;reaction between aldehyde and hydroxy grp. chair

  5. GLUCOSE:Isomerism • 1. D and L isomerism: • mirror images • relation to glyceraldehyde • orientation of –H & -OH grp around C adjacent to terminal C. • D; -OH grp on right hand side & vice versa, D- form abundant in mammals. • asymmetric carbon atoms confers optical activity • optical isomer are dextrorotatory (+) or levorotatory (–). • independent of the stereochemistry • 2. Pyranose and furanose ring structures:  • For glucose in solution, more than 99% is in the pyranose form. • 3.Alpha and beta anomers:  • Ring structure • Hemiacetal & hemiketal • Crystalline glu is α-D-glucopyranose •  in solution isomerism occurs about position 1, the carbonyl or anomeric carbon atom, to give a mixture of  α -glucopyranose (38%) and β -glucopyranose (62%).

  6. 4.Epimers: Isomers differing as a result of variations in configuration of the —OH and —H on carbon atoms 2, 3, and 4 of glucose are known as epimers. 4th is Galactose , glucose , 2nd mannose.

  7. Glycosides formed by condensation between the hydroxyl group of the anomeric carbon of a monosaccharide, and a second compound that may or may not (in the case of an aglycone) be another monosaccharide. aglycone (methanol, glycerol, sterol, phenol, N base;amine-N-glycosidic bond) Important glycosides cardiac glycosides( contain steroids as the aglycone) derivatives of digitalis and strophanthus such as ouabain Streptomycin Phlorhizin

  8. DISACCHARIDES -D-glucopyranosyl-(1 6)- O- -D-glucopyranosyl-(1 4)- O- -D-galactopyranosyl-(1 4)- O- -D-galactopyranosyl-(1 4)- O- -D-glucopyranosyl-(1 2)- O- -D-glucopyranosyl-(1 1)- O-

  9. Polysaccharides Serve Storage & Structural Functions Starch homopolymer, called a glucosan or glucan. most important dietary source of carbohydrate. constituents are amylose (13–20%), nonbranching helical structure, and amylopectin (80–85%), Glycogen storage polysaccharide. D-glucopyranose residues (in 1 4 glucosidic linkage) with branching by means of 1 6 glucosidic bonds . Inulin polysaccharide of fructose ,used to determine the glomerular filtration rate, Dextrins are intermediates in the hydrolysis of starch. Cellulose insoluble -D-glucopyranose 1 4 bonds cross-linking hydrogen bonds. Chitin exoskeleton of crustaceans and insects.

  10. Glycosaminoglycans (mucopolysaccharides) are complex carbohydrates containing amino sugars and uronic acids. They may be attached to a protein molecule to form a proteoglycan. Carbohydrates Found in Glycoproteins. Hexoses Mannose (Man), galactose (Gal) Acetyl hexosamines N-Acetylglucosamine (GlcNAc), N-acetylgalactosamine (GalNAc) Pentoses Arabinose (Ara), Xylose (Xyl) Methyl pentose L-Fucose (Fuc, see Fig. 14–15) Sialic acids N-Acyl derivatives of neuraminic acid; the predominant sialic acid is N-acetylneuraminic acid (NeuAc, see Fig. 14–16)

  11. CARBOHYDRATES OCCUR IN CELL MEMBRANES & IN LIPOPROTEINS • 5% of the weight of cell membranes is carbohydrate, in glycoproteins and glycolipids. • Their presence on the outer surface of the plasma membrane (the glycocalyx) has been shown with the use of plant lectins,eg, concanavalin A binds -glucosyl and -mannosyl residues. • Glycophorin integral membrane glycoprotein of erythrocytes. 130 amino acid residues. • Carbohydrates are also present in apo-protein B of plasma lipoproteins.

  12. INTERMEDIARY METABOLISM

  13. GLYCOLYSIS • MAJOR PATHWAY FOR GLUCOSE METABOLISM. • CONVERSION OF GLUCOSE TO 3 C-UNIT • RBC’s;ANAEROBIC GLYCOLYSIS. • ALSO FOR FRUCTOSE ,GALACTOSE AND OTHER CARBS. • ANAEROBIC GLYCOLYSIS ALLOWS SKELETAL MUSCLE TO PERFORM AT VERY HIGHER LEVEL. • DISEASES ASSOCIATED WITH ENZYMES OF GLYCOLYSIS ARE MAINLY SEEN IN HEMOLYTIC ANEMIAS(ALDOLASE A & PK) AND IN SKELETAL MUSCLE (PFK)AS FATIGUE. • HIGH RATE OF GLYCOLYSIS IN FAST GROWING CANCER CELL;FORMATION OF LACTATE. • LACTIC ACIDOSIS;PDH

  14. SUB-CELLULAR SITE:CYTOSOL. • IN ALL TISSUES EXCEPT LIVER AND PANCREATIC β –ISLET CELLS AVAILABILITY OF GLUCOSE FOR GLYCOLYSIS (OR GLYCOGEN SYN. IN MUSCLES AND LIPOGENESIS IN ADIPOSE TISSUE) IS REGULATED BY INSULIN. • REACTIONS: • 1.HEXOKINASE/GLUCOKINASE • HEXOKINASE IS NONSPECIFIC,STABLE,FOUND IN ALL TISSUES, INHIBITED BY GLUOSE 6-PHOSPHATE, LOW Km, *(0.1)mM ,NO EFFECT OF INSULIN,MAKES GLUCOSE AVAILABLE FOR OXIDATION. • GLUCOKINASE IS SPECIFIC,LABILE,FOUND IN ADULT LIVER, NOT INHIBITED BY G6P, HIGH Km(10 mM), DEPRESSED IN FASTING AND DM, INCREASED BY FEEDING GLUCOSE, INDUCED BY INSULIN, CLEARS GLUCOSE AFTER MEAL*(<100 mg/dl).

  15. ARSENATE/Pi=1-ARSENO-3-PHOSPHOGLYCERATE Mn2+

  16. REGULATION OF GLYCOLYSIS INSULIN FAVOURS GLYCOLYSIS;GLUCAGON/GLUCOCORTICOID INHIBITS. 1. HEXOKINASE(NOT COMMITED) 2. PHOSPHOFRUCTOKINASE-1(PFK-1) +ve REGULATOR-AMP(5’AMP),FRUCTOSE 2-6-BISPHOSPHATE - veREGULATOR-ATP,CITRATE,LOW Ph FRUCTOSE 2-6-BISPHOSPHATE(F-2-6-BP) ROLE: PFK-2(P)INACTIVE,F-2-6-BPase(P)ACTIVE= FORMATION OF F-6-P PFK-2(DeP)ACTIVE, F-2-6-BPase(DeP)INACTIVE= FORMATION OF F-2-6-BP 3. PYRUVATE KINASE +REGULATOR-FRUCTOSE 1-6-BISPHOSPHATE -REGULATOR-ATP,ALANINE PK DEFICIENCY IS SECOND MOST COMMON CAUSE (AFTER G6PD) OF ENZYME DEFICIENCY RELATED HEMOLYTIC ANEMIA(95%).4% EXHIBIT PHOSPHOGLUCOSE ISOMERASE DEFICIENCY.

  17. PASTEUR EFFECT: INHIBITORY EFFECT OF OXYGEN ON GLYCOLYSIS. • CRABTREE EFFECT: O2 CONSTANT,CONC. GLUCOSE HIGH, RESULTING ANAEROBIOSIS • NET GAIN OF ATP PER MOLE OF GLUCOSE • UNDER AEROBIC CONDITION:8 • UNDER ANAEROBIC CONDITION :2 • HIGH FRUTOSE INTAKE & OBESITY • FRUCTOSE • FRUCTOKINASE • FRUCTOSE-1-PHOSPHATE • FRUCTOSE INTOLERANCE ALDOLASE B • D-GLYCERALDEHYDE • TRIOSE KINASE • GLYCERALDEHYDE-3-PHOSPHATE • BYPASS REGULATORY STEP: FORMATION OF MORE PYRUVTE(ACETYL COA)

  18. GLUCOSE TRANSPORTERS family of proteins called the solute carriers (SLC) GLUT1: RBC’s GLUT2 :intestine, pancreatic β-cells, kidney and liver(glucose sensor) GLUT3: binds glucose with high affinity GLUT4: insulin-sensitive tissues, such as skeletal muscle and adipose tissue GLUT5: fructose transporter

  19. 2-3-BPG BIND TO Hb, DECREASE ITS AFFINITY TO O2, INCREASE O2 AVALABILITY TO TISSUE.

  20. FRUCTOSE METABOLISM Hereditary fructose-1,6-bisphosphatase deficiency results in severely impaired hepatic gluconeogenesis and leads to episodes of hypoglycemia, apnea, hyperventillation, ketosis and lactic acidosis.

  21. GALACTOSE METABOLISM SORBITOL/

  22. Lactose Synthesis Lactose, known as the “milk sugar,” is produced by the mammary glands of most mammals. Lactose is synthesized in the Golgi by lactose synthase (UDP-galactose:glucose galactosyltransferase), which transfers galactose from UDP-galactose to glucose, releasing UDP. This enzyme is composed of two proteins, A and B. Protein A is a β-D-galactosyltransferase, and is found in a number of body tissues. In tissues other than the lactating mammary gland, this enzyme transfers galactose from UDP-galactose to N-acetyl-D-glucosamine, and producing N-acetyllactosamine. In contrast, protein B is found only in lactating mammary glands. It is α-lactalbumin, and its synthesis is stimulated by the peptide hormone, prolactin. Protein B forms a complex with the enzyme, protein A, changing the specificity of that transferase so that lactose, rather than N-acetyllactosamine, is produced

  23. Conversion of glucose to fructose via sorbitol Synthesis of sorbitol: ~Aldose reductase reduces glucose, producing sorbitol (glucitol). ~This enzyme is found, in lens, retina, Schwann cells, liver, kidney, placenta, red blood cells, and in cells of the ovaries and seminal vesicles ~In cells of the liver, ovaries, sperm, and seminal vesicles, there is a second enzyme, sorbitol dehydrogenase, that can oxidize the sorbitol to produce fructose sperm cells use fructose . ~pathway from sorbitol to fructose in the liver provides a mechanism by which any available sorbitol is converted into a substrate that can enter glycolysis or gluconeogenesis.

  24. The effect of hyperglycemia on sorbitol metabolism:  Because insulin is not required for the entry of glucose into the cells where sorbitol syn. occurs. large amounts of glucose may enter during hyperglycemia (uncontrolled diabetes). Elevated intracellular glucose produce a significant increase in the amount of sorbitol, which cannot pass efficiently through cell membranes and, therefore, remains trapped inside the cell. This is exacerbated when sorbitol dehydrogenase is low or absent(in retina, lens, kidney, and nerve cells). result, sorbitol accumulates in these cells(strong osmotic effects (cataract formation, peripheral neuropathy, and vascular problems leading to nephropathy and retinopathy)

  25. OXIDATION OF PYRUVATE TO ACETYL COA—PDH COMPLEX Pyruvate + CoA + NAD+ ----> CO2 + acetyl-CoA + NADH + H+ • THREE ENZYMATIC ACTIVITY OF PDH • PYRUVATE DEHYDROGENASE • DIHYDROLIPOYL TRANSACETYLASE • DIHYDROLIPOYL DEHYDROGENASE • 5 COENZYME ASSOCIATED • 1.THIAMINE PYROPHOSPHATE 4.FAD • 2.LIPOIC ACID 5.NAD • 3.COENZYME A

  26. PDH REGULATION • 1.END PRODUCT INHIBITION(ACETYL COA,NADH) • 2.COVELENT MODIFICATION • PDH (PHOSPHORYLATED BY KINASE,DECREASE ACTIVITY) • 3.ATP,ACETYL COA,NADH • ARSENITE,MERCURIC ION INHIBIT PDH • DIETARY DEFICIENCY OF THIAMINE RESULTS IN PYRUVATE ACCUMULATION • PYRUVIC AND LACTIC ACIDOSIS IN ALCOHOLICS • INHERITED PDH DEFICIENCY

  27. TCA CYCLE • sequence of reactions in mitochondria • oxidizes the acetyl moiety of acetyl-CoA • reduces coenzymes that are reoxidized through the electron transport chain • final common pathway for the oxidation of carbohydrate, lipid, and protein • Role of vitamins • RIBOFLAVIN-as FAD,cofactor for succinate dehydrogenase . • NIACIN-as NAD,e- acceptor for isocitrate dh,α-ketoglutarate dh,malate dh • THIAMINE-as thiamine di phosphate,coenzyme for decarboxylation: α-ketoglutarate dh. • PENTOTHENIC ACID-as part of coenzyme A, acetyl coA,succnyl coA. • Substrate level phosphorylation • Production of ATP without participation of ETC.

  28. NADH TRANSPORT VIA MALATE SHUTTLE 6 ATP;GLYCERALDEHYDE SHUTTLE 4 ATP.

  29. REGULATORY STEP -NADH,SUCCINYL COA ATP NADH ADP NAD+ REGULATORY STEP: +ADP,Ca -NADH,ATP REGULATORY STEP: -NADH,SUCCINYL COA

  30. GLYCOGEN METABOLISM • MAIN STORE ARE FOUND IN SKELETAL MUSCLE(FUEL RESERVE) AND LIVER(TO MAINTAIN BLOOD GLUCOSE). • BRANCHED CHAIN HOMOPOLYSACCHARIDE(α-D-GLUCOSE) • PRIMARY GLYCOSIDIC BOND AFTER 8-10 GLUCOSYL RESIDUES; α(1—4). • BRANCH POINT α(1—6). • MW 108 D. • LIVER GLYCOGEN FLUCTUATES DURING WELL FED AND FASTING.

  31. GLYCOGEN SYNTHESIS

  32. GLYCOGEN DEGRADATION

  33. REGULATION • IN WELL FED STATE DURING MUSCLE CONTRACTION----Ca IS RELEASED FROM ER---FORMATION OF CALCIUM CALMODULIN COMPLEX-----BINDING OF Ca-Cal COMPLEX TO Ca DEPENDENT PHOSPHORYLASE KINASE ACTIVATING IT(WITHOUT cAMP DEPENDENT PK)-----ACTIVATION OF PHOSPHORYLASE. IN MUSCLE UNDER EXTREME CONDITION OF ANOXIA---- ATP------AMP ACTIVATES GLYCOGEN PHOSPHORYLASE WITHOUT PHOSPHORYLATION.

  34. ACTIVATION OF GLYCOGENOLYSIS BY cAMP DIRECTED PATHWAY

  35. REGULATION OF GLYCOGEN SYNTHESIS

  36. Lysosomal  1 4 and  1

  37. GLUCONEOGENESIS • OCCURRENCE: TISSUE WHICH NEEDS CONTINUOUS SUPPLY OF GLUCOSE (BRAIN ,RBC,KIDNEY MEDULLA,LENS CORNEA,TESTES& EXERCISING MUSCLE) • DURING PROLONGED FAST,AFTER DEPLETION OF LIVER GLYCOGEN STORAGE. • SUBSTRATES FOR GLUCONEOGENESIS: • GLYCEROL:HYDROLYSIS OF TAG,PHOSPHORYLATED TO GLYCEROL PHOSPHATE BY GLYCEROL KINASE,OXIDISED BY GLYCEROL PHOSPHATE DEHYDROGENASE TO DIHYDROXYACETONE PHOSPHATE. • LACTATE(CORI’S CYCLE) • AMINO ACIDS:GLUCOGENIC—α-KETOACIDS (OXALOACETATE, • α- KETOGLUTARATE )

  38. THREE IRREVERSIBLE REACTION OF GLYCOLYSIS IS CIRCUMVENTED • PYRUVATE & PHOSPHOENOL PYRUVATE • ~ MITOCHONDRIA- PYRUVATE CARBOXYLASE ;CONVERSION OF PYRUVATE TO OXALOACETATE(ATP,BIOTIN COENZYME) • ~ OXALOACETATE IS REDUCED TO MALATE TRANSPORTED TO CYTOSOL, OXIDISED TO OXALOACETATE. • ~OXALOACETATE CONVERTED TO PHOSPHOENOLPYRUVATE BY PEP-CARBOXYKINASE . • ~PYRUVATE CARBOXYLASE IS ALLOSTERICALLY ACTIVATED BY ACETYL COA • ~REVERSE OF GLYCOLYSIS PROCEED TILL FRUCTOSE 1,6-BISPHOSPHATE. • ~GLUCAGON INCREASES TRANSCRIPTION OF PEP-CK.

  39. 2. FRUCTOSE 1,6-BISPHOSPHATE/ FRUCTOSE-6-PHOSPHATE ~HYDROLYSIS OF FRUCTOSE 1,6-BISPHOSPHATE BY FRUCTOSE 1,6-BISPHOSPHATASE ~FRUCTOSE 1,6-BISPHOSPHATASE IS INHIBITED BY FRUCTOSE 2,6-BISPHOSPHATE. 3.GLUCOSE6-PHOSPHATE/GLUCOSE ~HYDROLYSIS OF G6P BY GLUCOSE 6-PHOSPHATASE ~LIVER & KIDNEY ~G-6-PASE IS E R ENZ ~G6P TRANSLOCASE TRANSPORT G6P ACROSS ER ~GLUCOSE 6-PHOSPHATASE REMOVES PHOSPHATE PRODUCING FREE GLUCOSE. ~MUSCLE LACKS GLUCOSE 6-PHOSPHATASE;MUSCLE GLUCOSE IS NOT USED TO MAINTAIN BLOOD GLUCOSE.

  40. PENTOSE PHOSPHATE PATHWAY • OCCURANCE CYTOSOL • TWO IRREVERSIBLE OXIDATIVE REACTION FOLLOWED BY REVERSIBLE SUGAR PHOSPHATE INTERCONVERSION • IRREVERSIBLE OXIDATIVE REACTION • LEADS TO FORMATION OF RIBULOSE 5-PHOSPHATE,CO2 AND • 2 MOLECULE OF NADPH • IMPORTANCE IN • LIVER SYNTHESIS • LACTATING MAMMARY GLAND OF • ADIPOSE TISSUE FATTY ACIDS • ADRENAL COTEX-NADPH DEPENDENT SYN. OF STEROIDS • ERYTHROCYTES-REDUCTION OF GLUTATHIONE

  41. G6PD STEP IS THE REGULATORY STEP OF THE PATHWAY • INCREASED NADPH/NADP+ RATIO INHIBIT G6PD • INSULIN ENHANCES G6PD GENE EXPRESION • IRREVERSIBLE NONOXIDATIVE REACTIONS OF PATHWAY OCCURS IN ALL CELL TYPES SYN. NUCLIC ACIDS • RIBOSE – 5 PHOSPHATE SYNTHESIS OF DNA & RNA • MANY CELLS WHICH NEED NADPH FOR REDUCTIVE BIOSYNTHETIC REACTION EMPLOY 1. TRANSKETOLASE(TRANSFER 2 – C UNITS) • 2. TRANSALDOLASE(TRANSFER 3 – C UNITS) • FOR CONVERSION OF RIBOSE – 5 PHOSPHATE GLYCERALDEHYDE 3 PHOSPHATE & FRUCTOSE – 6 PHOSPHATE (INTERMEDIATE OF GLYCOLYSIS)

  42. ENZYME REQUIRING TPP • PYRUVATE DECARBOXYLASE • a -KETO GLUTARATE (TCA) • TRANSKETOLASE • BRANCHED CHAIN a- KETO ACID DEHYDROGENASE

  43. NADPH • ELECTRONS OF NADPH IS USED FOR REDUCTIVE BIOSYNTHESIS (NADH;TRANSFER OF OXYGEN). FATTY ACID SYN. CHOLESTEROL SYN. NEUROTRANSMITTER SYN. NUCLEOTIDE SYN. • REDUCTION OF H2O2BY REDUCED GLUTATHION CATALYSED BY SELENIUM REQUIRING GLUTATHION PEROXIDASE,REGENERATION OF REDUCED GLUTATHION BY GLUTATHIONE REDUTASE REQUIRE NADPH. ~ SUPEROXIDE DISMUTASE AND CATALASE;REDUCTION OF ROS. ~ANTIOXIDANT CHEMICALS;DETOXIFY OXYGEN INTERMEDIATES IN LAB ONLY.(ASCORBATE,VIT A,β-CAROTENE. • CYTOCHROME P450 MONOOXYGENASE SYSTEM R-H + O2 + NADPH + H+ R-OH + H2O +NADP+

  44. ~MITOCHONDRIAL SYSTEM • 1.HYDROXYLATION OF STEROID HORMONE • 2.BILE ACID SYN. • 3.25-HYDROXYCHOLECALCIFEROL—1,25-DIHYDROXY FORM • ~MICROSOMAL SYSTEM • 1. SYS. FOUND IN ASSOCIATION OF SER(IN LIVER,SP) • 2.DETOXIFICATION OF FOREIGN COMPOUNDS(XENOBIOTICS) • 3. NEW OH-GRP SITE FOR CONJUGATION WITH GLUCURONATE • PHAGOCYTOSIS OXYGEN INDEPENDENT USES PH CHANGE IN PHAGOLYSOSOME

  45. OXYGEN DEPENDENT NADPH OXIDASE DEFICIENCY—CHRONIC GRANULOMATOUS DISEASE —PERSISTENT INFECTION , FORMATION OF GRANULOMAS

  46. THE RESPIRATORY CHAIN AND OXIDATIVE PHOSPHORYLATION

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