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Chapter 5 Carbohydrate Metabolism Lecture 1 Lecture 2 Lecture 3 Lecture 4 Lecture 5 Lecture 6 Function of carbohydrate The classification of carbohydrates Glycolysis The fates of pyruvate Gluconeogenesis The pentose phosphate pathway of glucose oxidation Lecture 7 Citric acid cycle Lecture 1 Function of carbohydrate Chapter 8 Carbohydrates What are Carbohydrates (saccharides) ? Carbohydrate is an organic compound with the general formula Cm(H2O)n, which consists of carbon, hydrogen and oxygen, the last two in the 2:1 atom ratio. Carbohydrates are hydrates of carbon, hence their name. Carbohydrate, (C-H2O)n = “Carbon + Water” Where are Carbohydrates? Function of Carbohydrates ? Upland cotton produces the most widely used natural fibers, cellulose (polysaccharide) Cellulose: the most abundant organic compounds in the biosphere 1015 kg of cellulose is synthesized and degraded on earth each year Carbohydrates in food are important sources of energy. Energy sources and structural elements Energy sources Cell wall Energy sources and structural elements Bioactive substance——Glycoproteins and Glycolipids Function of Carbohydrates Source of energy Structure (cotton fibers: cellulose ) Building blocks Cellular recognition Lecture 2 The classification of carbohydrates (Saccharides ) 1 Monosaccharide • The generic name of the simplest carbohydrates. • Monosaccharides can not be hydrolysised to give smaller carbohydrates. Monosaccharides can be classified according to the number of carbons: Triose Tetrose Pentose Hexose Heptose 3 carbons 4 carbons 5 carbons 6 carbons 7 carbons Important hexose : Glucose , fructose , galactose, mannose D-Ribose Pentose: 2 Oligosaccharide Any molecule that contains a small number (2 to about 20) of monosaccharide residues connected by glycosidic linkages. Oligosaccharide Maltose 1 4 Sucrose It is formed by plants but not by animals. 1 2 1 2 Lactose Lactose occurs naturally in milk but rarely in plants. Cellobiose 3 Polysaccharide An alternative name for glycan ; Any linear or branched polymer consisting of monosaccharide residues. Important polysaccharides include glycogen, starch and cellulose . Starch Energy store of plants Amylose It can be made of several thousand glucose units. In amylose, the 1st carbon on one glucose molecule is linked to the 4th carbon on the next glucose molecule (α(1→4) bonds). Amylose is soluble in water. Amylopectin Glucose units are linked in a linear way with α(1→4) glycosidic bonds. Branching takes place with α(1→6) bonds occurring every 24 to 30 glucose units. It is not soluble in water. Glycogen Glycogen is found mainly in the liver and skeletal muscle. Muscle: energy (ATP) production. Liver: balance blood glucose levels. Cellulose A linear, unbranched β l-4 glucan molecular Lecture 3 Glycolysis Chapter 11 Glycolysis In glycolysis, a molecule of glucose is broken down in a series of enzyme-catalyzed reactions to yield two molecules of the three-carbon compound pyruvate . During the sequential reactions of glycolysis, some of the free energy released from glucose is conserved in the form of ATP and NADH. First stage of carbohydrate metabolism. Glycolysis was first discovered by Gustav Embden and Otto Meyerhof and Parnus. Glycolysis is named as EMP Simple sugars are broken down to pyruvate No oxygen needed. All life uses this process. There are 10 steps in glycolysis. 1 The Reaction of the glycolysis (Two Phases) Preparatory phase(step①-⑤): Phosphorylation of glucose and its conversion to glyceraldehyde 3phosphate Payoff phase(step⑥-⑩): Oxidative conversion of glyceraldehyde 3phosphate to pyruvate and the coupled formation of ATP and NADH (1) Phosphorylation of Glucose or glucokinase Transfer of a phosphoryl group from ATP to glucose (2) Isomerization :Conversion of Glucose 6Phosphate to Fructose 6-Phosphate (3) Phosphorylation of Fructose 6-Phosphate to Fructose 1,6-Bisphosphate (4) Cleavage of Fructose 1,6-Bisphosphate (5)Interconversion of the Triose Phosphates (6) Oxidation of Glyceraldehyde 3-Phosphate to 1,3-Bisphosphoglycerate Oxidation and phosphorylation, yielding a high-energy mixed-acid anhydride (7) Phosphoryl Transfer from 1,3-bisphosphoglycerate to ADP Transfer of a high-energy phosphoryl group to ADP, yielding ATP (8) Conversion of 3-Phosphoglycerate to 2-Phosphoglycerate (9) Dehydration to an energy-rich enol ester PEP (10) Transfer of the Phosphoryl Group from Phosphoenolpyruvate to ADP Transfer of a high-energy phosphoryl group to ADP, yielding ATP For each molecule of glucose that passes through the preparatory phase (a), two molecules of glyceraldehyde 3-phosphate are formed; both pass through the payoff phase (b), Pyruvate is the end product of the second phase of glycolysis. For each glucose molecule, two ATP are consumed in the preparatory phase and four ATP are produced in the payoff phase, giving a net yield of two ATP per molecule of glucose converted to pyruvate. The glycolytic breakdown of glucose is the sole source of metabolic energy in some mammalian tissues and cell types (erythrocytes, renal medulla, brain, and sperm, for example). Many anaerobic microorganisms are entirely dependent on glycolysis. ATP and NADH Formation Coupled to Glycolysis During glycolysis some of the energy of the glucose molecule is conserved in ATP, while much remains in the product, pyruvate. The overall equation for glycolysis is Regulation of glycolysis Three glycolytic reactions(the reactions catalyzed by hexokinase, PFK-1, and pyruvate kinase) are irreversible. 1. Phosphofructokinase (PFK) Inhibited by:ATP,Citrate Activated by:AMP, 2,6-bisphosphate(F-2,6-BP) 2 Hexokinase Inhibited by:G-6-P 3 pyruvate kinase Inhibited by:ATP Activated by:FBP Lecture 4 The fates of pyruvate Three catabolic routes. 1. oxidized to acetyl-CoA 2. Ethanol fermentation 3. Lactic acid fermentation Lactic acid fermentation Under anaerobic conditions, reduction of pyruvate provides a means of reoxidizing the NADH produced in the glyceraldehyde-3-phosphate dehydrogenase reaction of glycolysis converted to lactate. Lactic acid fermentation Ethanol fermentation The reduction of acetaldehyde to ethanol by NADH, under anaerobic conditions Ethanol fermentation Aerobic pathways for pyruvate The five coenzymes participating in this reaction: TPP, Lipoic Acid , CoA-SH, NAD+, FAD, The Pyruvate Dehydrogenase Complex Consists of Three Distinct Enzymes Pyruvate dehydrogenase (E1) Dihydrolipoyl transacetylase (E2) Dihydrolipoyl dehydrogenase(E3) FIGURE 16–5 The pyruvate dehydrogenase complex. FIGURE 16–6 Oxidative decarboxylation of pyruvate to acetyl-CoA by the PDH complex.