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PowerPoint® Lecture Slide Presentation by Vince Austin Human Anatomy & Physiology FIFTH EDITION Elaine N. Marieb Chapter 25 Nutrition, Metabolism, and Body Temperature Regulation Part B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Krebs Cycle: Preparatory Step • Occurs in mitochondrial matrix and is fueled by pyruvic acid and fatty acids Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Krebs Cycle: Preparatory Step • Pyruvic acid is converted to acetyl CoA in three main steps: • Decarboxylation • Carbon is removed from pyruvic acid • Carbon dioxide is released • Oxidation • Hydrogen atoms are removed from pyruvic acid • NAD+ is reduced to NADH + H+ • Formation of acetyl CoA – the resultant acetic acid is combined with coenzyme A, a sulfur-containing coenzyme, to form acetyl CoA Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Krebs Cycle • An eight-step cycle in which acetic acid is decarboxylated and oxidized, generating: • Three molecules of NADH + H+ • One molecule of FADH2 • Two molecules of CO2 • One molecule of ATP • For each molecule of glucose entering glycolysis, two molecules of acetyl CoA enter the Krebs cycle Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Krebs Cycle Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 25.7 Electron Transport Chain • Food (glucose) is oxidized and the hydrogen: • Are transported by coenzymes NADH and FADH2 • Enter a chain of proteins bound to metal atoms (cofactors) • Combine with molecular oxygen to form water • Release energy • The energy released is harnessed to attach inorganic phosphate groups (Pi) to ADP, making ATP by oxidative phosphorylation Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Hypothetical Mechanism of Oxidative Phosphorylation • The hydrogens delivered to the chain are split into protons (H+) and electrons • The protons are pumped across the inner mitochondrial membrane by: • NADH dehydrogenase (FMN, Fe-S) • Cytochrome b-c1 • Cytochrome oxidase (a-a3) • The electrons are shuttled from one acceptor to the next Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Hypothetical Mechanism of Oxidative Phosphorylation • Electrons are delivered to oxygen, forming oxygen ions • Oxygen ions attract H+ to form water • H+ pumped to the intermembrane space: • Diffuses back to the matrix via ATP synthase • Releases energy to make ATP Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Hypothetical Mechanism of Oxidative Phosphorylation Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 25.8 Electronic Energy Gradient • The transfer of energy from NADH + H+ and FADH2 to oxygen releases large amounts of energy • This energy is released in a stepwise manner through the electron transport chain • The electrochemical proton gradient across the inner membrane: • Creates a pH gradient • Generates a voltage gradient • These gradients cause H+ to flow back into the matrix via ATP synthase Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Electronic Energy Gradient Figure 25.9 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Summary of ATP Production Figure 25.10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Glycogenesis and Glycogenolysis • Glycogenesis – formation of glycogen when glucose supplies exceed cellular need for ATP synthesis • Glycogenolysis – breakdown of glycogen in response to low blood glucose Figure 25.11 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Gluconeogenesis • The process of forming sugar from noncarbohydrate molecules • Takes place mainly in the liver • Protects the body, especially the brain, from the damaging effects of hypoglycemia by ensuring ATP synthesis can continue Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Lipid Metabolism • Most products of fat metabolism are transported in lymph as chylomicrons • Lipids in chylomicrons are hydrolyzed by plasma enzymes and absorbed by cells • Only neutral fats are routinely oxidized for energy • Catabolism of fats involves two separate pathways • Glycerol pathway • Fatty acids pathway Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Lipid Metabolism • Glycerol is converted to glyceraldehyde phosphate • Glyceraldehyde is ultimately converted into acetyl CoA • Acetyl CoA enters the Krebs cycle • Fatty acids undergo beta oxidation which produces: • Two-carbon acetic acid fragments, which enter the Krebs cycle • Reduced coenzymes, which enter the electron transport chain Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Lipid Metabolism Figure 25.12 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Lipogenesis and Lipolysis • Excess dietary glycerol and fatty acids undergo lipogenesis to form triglycerides • Glucose is easily converted into fat since acetyl CoA is: • An intermediate in glucose catabolism • The starting molecule for the synthesis of fatty acids • Lipolysis, the breakdown of stored fat, is essentially lipogenesis in reverse • Oxaloacetic acid is necessary for the complete oxidation of fat • Without it, acetyl CoA is converted into ketones (ketogenesis) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Lipogenesis and Lipolysis Figure 25.13 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Lipid Metabolism: Synthesis of Structural Materials • Phospholipids are important components of myelin and cell membranes • The liver: • Synthesizes lipoproteins for transport of cholesterol and fats • Makes tissue factor, a clotting factor • Synthesizes cholesterol for acetyl CoA • Uses cholesterol for forming bile salts • Certain endocrine organs use cholesterol for synthesizing steroid hormones Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Protein Metabolism • Excess dietary protein results in amino acids being: • Oxidized for energy • Converted into fat for storage • Amino acids must be deaminated prior to oxidation for energy • Deaminated amino acids are converted into: • Pyruvic acid • One of the keto acid intermediates of the Krebs cycle • These events occur as transamination, oxidative deamination, and keto acid modification Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Oxidation of Amino Acids • Transamination – switching of an amine group from an amino acid to a keto acid (usually -ketoglutaric acid of the Krebs cycle) • Typically, glutamic acid is formed in this process • Oxidative deamination – the amine group of glutamic acid is: • Released as ammonia • Combined with carbon dioxide in the liver • Excreted as urea by the kidneys • Keto acid modification – keto acids from transamination are altered to produce metabolites that can enter the Krebs cycle Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Synthesis of Proteins • Amino acids are the most important anabolic nutrients, which form: • All protein structures • The bulk of the body’s functional molecules • Amounts and types of proteins: • Are hormonally controlled • Reflect each life cycle stage • A complete set of amino acids is necessary for protein synthesis • All essential amino acids must be provided in the diet Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings State of the Body • The body exists in a dynamic catabolic-anabolic state • Organic molecules (except DNA) are continuously broken down and rebuilt • The body’s total supply of nutrients constitutes its nutrient pool • Amino acid pool – body’s total supply of free amino acids is the source for: • Resynthesizing body proteins • Forming amino acid derivatives • Gluconeogenesis Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings State of the Body Figure 25.15 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Interconversion Pathways of Nutrients • Carbohydrates are easily and frequently converted into fats • Their pools are linked by key intermediates • They differ from the amino acid pool in that: • Fats and carbohydrates are oxidized directly to produce energy • Excess carbohydrate and fat can be stored Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Interconversion Pathways of Nutrients Figure 25.16 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Absorptive and Postabsorptive States • Metabolic controls equalize blood concentrations of nutrients between two states • Absorptive • The time during and shortly after nutrient intake • Postabsorptive • The time when the GI tract is empty • Energy sources are supplied by the breakdown of body reserves Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings