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Chapter 24A Nutrition, Metabolism, Body Temperature Slides by Barbara Heard and W. Rose. figures from Marieb & Hoehn 9th ed. Portions copyright Pearson Education Nutrition • Most ingested nutrients used for metabolic fuel • Some for cell structures and molecular synthesis • Energy value measured in kilocalories (kcal) – Heat needed to raise temperature of 1 kg H2O by 1C • What happens to absorbed nutrients? © 2013 Pearson Education, Inc. Nutrition • Nutrient - substance in food for growth, maintenance, repair • Major nutrients – bulk of ingested food – Carbohydrates, lipids, and proteins • Other nutrients – required in small amounts – Vitamins and minerals • Water required so technically a nutrient © 2013 Pearson Education, Inc. Nutrition • Food groups – Fruits – Vegetables – Grains – Protein – Dairy • Eat less overall; plenty of fruits, vegetables, whole grains; avoid junk food; exercise © 2013 Pearson Education, Inc. Nutrition • Liver can convert many molecules into those needed • Essential nutrients – Diet must provide; liver cannot synthesize – Possibly 50 molecules • Non-essential nutrients vital to life as well © 2013 Pearson Education, Inc. Carbohydrates • Dietary sources – primarily from plants – Starch (complex carbohydrates) in grains and vegetables – Sugars (mono- and disaccharides) in fruits, sugarcane, sugar beets, honey and milk – Fiber: not a source of calories cuz we can’t digest - cellulose in vegetables; provides roughage • ~4 kcal / g © 2013 Pearson Education, Inc. Carbohydrates: Uses in Body • Glucose - fuel used by cells to make ATP – Some cells use fats for energy • Neurons and RBCs ~ entirely on glucose; neurons die quickly without glucose • Excess glucose converted to glycogen or fat and stored • Fructose and galactose converted to glucose by liver © 2013 Pearson Education, Inc. Carbohydrates Dietary recommendations • Recommended intake - 45–65% of total calorie intake; mostly complex carbohydrates – Whole grains and vegetables • At least 130 g/day (male & female) Source: 2010 Dietary Guidelines for Americans http://www.health.gov/dietaryguidelines/dga2010/dietaryguidelines2010.pdf Lipids • Dietary sources – Triglycerides (neutral fats) • Saturated fats in meat, dairy foods, and tropical oils; hydrogenated oils (trans fats) • Unsaturated fats in seeds, nuts, olive oil, and most vegetable oils – Cholesterol in egg yolk, meats, organ meats, shellfish, and milk products • Liver makes ~85% cholesterol despite intake © 2013 Pearson Education, Inc. Triglyceride Cholesterol © 2013 Pearson Education, Inc. Testosterone Estradiol Lipids • Liver can interconvert many fatty acids • Essential fatty acids – Linoleic acid – Linolenic acid Found in most vegetable oils Linolenic 18C Linoleic 18C © 2013 Pearson Education, Inc. Lipids: Uses in Body • Help absorb fat-soluble vitamins • Major fuel of hepatocytes and skeletal muscle • Phospholipids essential in myelin sheaths and all cell membranes • Adipose tissue protection, insulation, fuel storage • Cholesterol stabilizes membranes; precursor of bile salts, steroid hormones • ~9 kcal / gram © 2013 Pearson Education, Inc. Lipids • Dietary guidelines* – Fats: 20-35% of total caloric intake – Saturated fats: <10% of calories (0% is OK) – Cholesterol: < 300 mg/day (0 mg is OK) • Goal – Keep cholesterol < 200 mg/dl • Typical American diet : Fats provide approx. 35% of calories* * 2010 Dietary Guidelines for Americans. No minimum lipid intake determined by Food & Nutrition Board, Inst. Of Med., 2002/2005. Proteins • Dietary sources – Eggs, milk, fish, most meats, soybeans contain complete proteins • Contain all needed amino acids – Legumes, nuts, and cereals contain incomplete proteins (lack some essential amino acids) – Legumes and cereal grains together contain all essential amino acids © 2013 Pearson Education, Inc. Proteins: Uses in Body • Structural materials – Keratin (skin); collagen and elastin (connective tissue); muscle proteins • Functional molecules – Enzymes, some hormones • Amino acids can be burned for energy • ~4 kcal / gram © 2013 Pearson Education, Inc. Proteins: Use of Amino Acids • All-or-none rule – All amino acids needed must be present for protein synthesis to occur; if not all present amino acids used for energy • Adequacy of caloric intake – Protein used as fuel if insufficient carbohydrate or fat available © 2013 Pearson Education, Inc. Proteins: Use of Amino Acids • Nitrogen balance – Rate of protein synthesis equals rate of breakdown and loss – Positive nitrogen balance - synthesis exceeds breakdown (normal in children, pregnant women, tissue repair) – Negative nitrogen balance - breakdown exceeds synthesis (e.g., stress, burns, infection, injury, poor dietary proteins, starvation) © 2013 Pearson Education, Inc. Figure 24.2 Essential amino acids. Tryptophan Methionine (Cysteine) Tryptophan Valine Methionine Threonine Total protein needs Valine Phenylalanine (Tyrosine) Threonine Leucine Phenylalanine Isoleucine Leucine Lysine Histidine (Infants) Beans and other legumes Corn and other grains Isoleucine Lysine Arginine (Infa nts) Essential amino acids © 2013 Pearson Education, Inc. Vegetarian diets providing the eight essential amino acids for humans Proteins • Dietary requirements – Needs reflect age, size, metabolic rate, nitrogen balance – 0.66 gram per kg body weight per day* – i.e. approx. 1.5 ounce protein/day for 155 lb person – American diet provides more than needed *Dietary Reference Intakes, Food & Nutrition Board, Institute Of Medicine (USA), 2002/2005, for adults. Recommended daily protein intake per kg is higher for children & pregnant & lactating women. © 2013 Pearson Education, Inc. Vitamins • • • • Organic compounds Crucial in helping body use nutrients Most function as coenzymes Vitamins D (skin), some B and K synthesized by intestinal bacteria; betacarotene (carrots) converted in body vitamin A • Rest must be ingested • No one food group contains all vitamins © 2013 Pearson Education, Inc. Vitamins • Water-soluble, fat-soluble • Water-soluble vitamins – B complex and C are absorbed with water – B12 absorption requires intrinsic factor – Not stored in the body • Any not used within an hour or so is excreted • Therefore megadoses offer little or no value © 2013 Pearson Education, Inc. Vitamins • Fat-soluble vitamins – A, D, E, and K absorbed with lipid digestion products – Stored in body, except for vitamin K • Pathologies due to excess © 2013 Pearson Education, Inc. Vitamins • Free radicals generated during normal metabolism – Vitamins C, E, A, and mineral selenium antioxidants • Neutralize free radicals • Broccoli, cauliflower, brussels sprouts good sources of vitamins A and C © 2013 Pearson Education, Inc. Minerals • Seven required in moderate* amounts – Calcium, phosphorus, potassium, sodium, chlorine, magnesium, sulfur • Others required in trace amounts – Fe, Zn top the list at 8-18 mg/day • Work with nutrients to ensure proper body functioning • Uptake and excretion balanced to prevent toxic overload * 0.3 to 4 g/day in adults. No DRI for S since adequate protein intake will yield enough. See DRI Tables, Food & Nutrition Board, IOM, 1997-2011. © 2013 Pearson Education, Inc. Minerals • Examples – Calcium, phosphorus, and magnesium salts harden bone – Iron essential for oxygen binding to hemoglobin – Iodine necessary for thyroid hormone synthesis – Sodium and chloride major electrolytes in blood • Mineral-rich foods – Vegetables, legumes, milk, some meats © 2013 Pearson Education, Inc. Metabolism • Metabolism - biochemical reactions inside cells involving nutrients • Two types of reactions – Anabolism - synthesis of large molecules from small ones • Ex. Amino acids proteins – Catabolism - hydrolysis of complex structures to simpler ones • Ex. Proteins amino acids © 2013 Pearson Education, Inc. Metabolism • Cellular respiration – Catabolism of food fuels capture of energy to form ATP in cells • Enzymes shift high-energy phosphate groups of ATP to other molecules (phosphorylation) • Phosphorylated molecules activated to perform cellular functions © 2013 Pearson Education, Inc. Stages of Metabolism • Three stages in processing nutrients – Digestion, absorption, and transport to tissues – Cellular processing (in cytoplasm) • Synthesis of lipids, proteins, and glycogen, or • Catabolism (glycolysis) into pyruvic acid and acetyl CoA – Oxidative (mitochondrial) breakdown of intermediates into CO2, water, and ATP © 2013 Pearson Education, Inc. Cellular Respiration • Goal trap chemical energy in ATP – Energy also stored in glycogen and fats – Oxidation of food for fuel • Step by step removal of pairs of hydrogen atoms (and electron pairs) from substrates only CO2 left • Includes glycolysis, Krebs cycle, oxidative phosphorylation © 2013 Pearson Education, Inc. Figure 24.3 Three stages of metabolism of energy-containing nutrients. Stage 1 Digestion in GI tract lumen to absorbable forms. PROTEINS Transport via blood to tissue cells. CARBOHYDRATES FATS Glucose and other sugars Glycerol Fatty acids Amino acids Stage 2 Anabolism (incorporation into molecules) and catabolism of nutrients to form intermediates within tissue cells. © 2013 Pearson Education, Inc. Glycogen Pyruvic acid Infrequent Stage 3 Oxidative breakdown of stage 2 products occurs in mitochondria of tissue cells. CO2 is liberated, and H atoms removed are ultimately delivered to molecular oxygen, forming water. Some energy released is used to form ATP. Catabolic reactions Anabolic reactions Glycolysis Glucose Proteins Acetyl CoA Krebs cycle Oxidative phosphorylation (in electron transport chain) Fats ATP Synthesis • Two mechanisms – Substrate-level phosphorylation • A small contribution, in cytoplasm – Oxidative phosphorylation • The majority of ATP made this way; in mitochondria • Chemiosmotic process • ATP synthase © 2013 Pearson Education, Inc. Mechanisms of phosphorylation: Oxidative phosphorylation High H+ concentration in intermembrane space Membrane Proton pumps (electron transport chain) ATP synthase Energy from food Low H+ concentration in mitochondrial matrix © 2013 Pearson Education, Inc. Carbohydrate Metabolism Glucose enters cell by facilitated diffusion Complete glucose catabolism requires three pathways • Glycolysis (cytoplasm) • Krebs cycle (mitochondrial matrix) • Electron transport chain and oxidative phosphorylation (mitochodrial inner membrane) © 2013 Pearson Education, Inc. ATP formation by cellular respiration, in cytosol and mitochondria. Chemical energy (high-energy electrons) Chemical energy Glycolysis Glucose Cytosol Electron transport chain and oxidative phosphorylation Krebs cycle Pyruvic acid Inner mitochondrial membrane (cristae) Mitochondrion Via oxidative phosphorylation Via substrate-level phosphorylation 1 Glycolysis, in the cytosol, breaks down each glucose molecule into two molecules of pyruvic acid. 2 The pyruvic acid then enters the mitochondrial matrix, where the Krebs cycle decomposes it to CO2. During glycolysis and the Krebs cycle, substrate-level phosphorylation forms small amounts of ATP. 3 Energy-rich electrons picked up by coenzymes are transferred to the electron transport chain, built into the cristae membrane. The electron transport chain carries out oxidative phosphorylation, which accounts for most of the ATP generated by cellular respiration. Carbohydrate Metabolism Net result of complete oxidation of glucose (aerobic: with O2) C6H12O6 + 6O2 6H2O + 6CO2 + ~30 ATP + heat © 2013 Pearson Education, Inc. Carbohydrate Metabolism Glycolysis: Initial stage of glucose breakdown • Occurs in cytoplasm • Does not require oxygen 1 glucose + 2 ADP +2 Pi + 2 NAD+ 2 pyruvate + 2 ATP + 2 NADH © 2013 Pearson Education, Inc. Carbohydrate Metabolism Glycolysis requires NAD+ to work After glycolysis (2 pyruvate + 2 ATP + 2 NADH): • If there’s O2: – Pyruvates enter TCA cycle – NADH gets oxidized with the help of the electron transport chain (oxidative phosphorylation) • If there’s NOT O2: – NADH reacts with pyruvate to make NAD+ and lactic acid © 2013 Pearson Education, Inc. Glycolysis • Fate of lactic acid: – Some leaves cell and goes to liver • May be converted to glucose-6-phosphate (G6P) • G6P stored as glycogen or de-phosphorylated to make glucose • Prolonged anaerobic metabolism causes acid build-up: lactic acidosis • Glycolysis: makes ATP faster than aerobic respiration; yields much less ATP © 2013 Pearson Education, Inc. Krebs Cycle • Occurs in mitochondrial matrix • Fueled by pyruvic acid and fatty acids • Transitional phase converts each pyruvic acid to acetyl CoA in three steps • Decarboxylation - removal of 1 C to produce acetic acid and CO2 • Oxidation – H atoms removed from acetic acid; picked up by NAD+ NADH + H+ • Forms acetyl CoA: Acetic acid + coenzyme A acetyl coenzyme A (acetyl CoA) © 2013 Pearson Education, Inc. Krebs Cycle • Products of each turn of Krebs cycle – 3 NADH + H+, 1 FADH2, 2 CO2, 1 ATP • 1 glucose 2 pyruvic acid molecules two turns of Krebs cycle final products – 6 NADH + H+, 2 FADH2, 4 CO2, 2 ATP • Adding products of transitional phase, final products – 8 NADH + H+, 2 FADH2, 6 CO2, 2 ATP © 2013 Pearson Education, Inc. Krebs Cycle • Does not directly use O2 – NADH molecules must be oxidized in electron transport chain for Krebs cycle to continue © 2013 Pearson Education, Inc. Electron Transport Chain and Oxidative Phosphorylation • Directly uses oxygen • Overview – NADH + H+ and FADH2 (from glycolysis and Krebs cycle) deliver hydrogen atoms – Hydrogen atoms combined with O2 water – Released energy harnessed ATP by oxidative phosphorylation © 2013 Pearson Education, Inc. Electron Transport Chain and Oxidative Phosphorylation • Involves chain of proteins bound to metal atoms (cofactors) on inner mitochondrial membrane – Some – flavins - derived from riboflavin – Most – cytochromes – iron-containing pigments – Neighboring carriers form four respiratory enzyme complexes • Alternately reduced and oxidized as pick up and pass electrons © 2013 Pearson Education, Inc. Electron Transport Chain and Oxidative Phosphorylation • Pumped H+ creates electrochemical proton gradient – Created pH gradient; voltage across membrane – H+ attracted to matrix side of membrane by pH gradient and voltage – H+ diffuses back to matrix via ATP synthase electrical current – ATP synthase uses electrical current ATP PLAY Animation: Electron Transport © 2013 Pearson Education, Inc. Electron Transport Chain and Oxidative Phosphorylation • Transfer of energy from NADH + H+ and FADH2 to oxygen releases large amounts of energy • Energy released in controlled steps through electron transport chain • Electron pairs + oxygen atom O– – O– attracts H+ water © 2013 Pearson Education, Inc. Figure 24.8 Oxidative phosphorylation has two phases. Glycolysis Outer mitochondrial membrane Phase 1: Electron transport creates the proton gradient. Phase 2: Chemiosmosis uses the proton gradient to synthesize ATP. Intermembrane space Inner mitochondrial membrane (crista) III I Electron transport Krebs chain and oxidative cycle phosphorylation IV II ATP V synthase 1 Reduced coenzymes (NADH + H+ and FADH2) deliver electrons picked up during the oxidation of food fuels to respiratory enzyme complexes I and II. Mitochondrial matrix © 2013 Pearson Education, Inc. 2 The electrons are transferred from one complex to another in the membrane. Each complex is reduced and then oxidized, releasing energy that is used to pump H+ into the intermembrane space. This creates an electrochemical gradient between the matrix and the intermembrane space. Coenzyme Q (ubiquinone) and cytochrome c are mobile carriers that shuttle between the larger complexes. 3 At respiratory enzyme complex IV, electron pairs combine with two protons (H+) and a half molecule of O2, forming water. 4 Complex V, called ATP synthase, harnesses energy of the proton gradient to synthesize ATP. As H+ flows back across the membrane through ATP synthase, the synthase rotor spins, causing Pi to attach to ADP, forming ATP. Structure and function of ATP synthase Intermembrane space A rotor in the membrane spins clockwise when H+ flows through it down the H+ gradient. A stator anchored in the membrane holds the knob stationary. As the rotor spins, a rod connecting the cylindrical rotor and knob also spins. Mitochondrial matrix The protruding, stationary knob contains three catalytic sites that join inorganic phosphate to ADP to make ATP when the rod is spinning. © 2013 Pearson Education, Inc. ATP synthase animation. Shows H+ going from intermembrane space below to matrix above. Source: www.bioc.aecom.yu.edu/labs/girvlab/ATPase/ATPsynthase.mov. KAAP ATP synthase animation. Makes 3 ATP / rev. Inytermembrane space below, matrix above. ATP=pink, ADP=green, Pi=blue. H+ not shown. Source: MRC (UK). KAAP Summary of ATP Production • Energy use at rest averages 100 kcal/hour = 116 watts – Huge demand on mitochondria • 1 mole glucose = 686 kcal; 262 kcal captured in ATP (rest lost as heat) – 38% efficiency – Man-made machines ~ 10–30% efficiency © 2013 Pearson Education, Inc. Summary of ATP Production • Complete oxidation of 1 glucose molecule • Glycolysis + Krebs cycle + electron transport chain CO2 + H2O 32 molecules ATP – By both substrate-level and oxidative phosphorylation • But, energy required to move NADH + H+ generated in glycolysis into mitochondria final total ~ 30 molecules ATP – Total not exact, partly due to unclear stoichiometry of ATP synthase © 2013 Pearson Education, Inc. Energy yield during cellular respiration Mitochondrion Cytosol Electron shuttle across mitochondrial membrane Glycolysis Glucose Pyruvic acid 2 Acetyl CoA Krebs cycle Electron transport chain and oxidative phosphorylation (4 ATP – 2 ATP used for activation energy) by substrate-level phosphorylation by substrate-level phosphorylation Typical ATP yield per glucose © 2013 Pearson Education, Inc. by oxidative phosphorylation Glycogenesis and Glycogenolysis • Glycogenesis – Glycogen formation via glycogen synthase when glucose supplies exceed need for ATP synthesis – Mostly in liver and skeletal muscle • Glycogenolysis – Glycogen breakdown via glycogen phosphorylase in response to low blood glucose – Only by hepatocytes, some kidney and intestinal cells © 2013 Pearson Education, Inc. Glycogenesis and glycogenolysis Blood glucose Cell exterior Hexokinase (all tissue cells) Glucose-6phosphatase (present in liver, kidney, and intestinal cells) Glucose-6-phosphate Glycogenolysis Glycogenesis Mutase Mutase Glucose-1-phosphate Pyrophosphorylase Glycogen phosphorylase Uridine diphosphate glucose Cell interior Glycogen synthase Glycogen © 2013 Pearson Education, Inc. Athletes and Carbohydrates • Complex carbohydrates more glycogen storage in muscle; more effective than high-protein meal for intense muscle activity • Carbo loading – Carbohydrate-rich diet for 3-4 days; decreased activity muscles store more glycogen – improved performance and endurance © 2013 Pearson Education, Inc. Gluconeogenesis • Glucose formed in liver from glycerol and amino acids when blood glucose levels drop • Protects against damaging effects of hypoglycemia – Especially important for nervous system © 2013 Pearson Education, Inc. Lipid Metabolism • Greater energy yield than from glucose or protein catabolism – Fat catabolism yields 9 kcal per gram versus 4 kcal per gram of carbohydrate or protein • Most products of fat digestion transported in lymph as chylomicrons • Hydrolyzed by endothelial enzymes into fatty acids and glycerol © 2013 Pearson Education, Inc. Lipid Metabolism • Only triglycerides routinely oxidized for energy • Two building blocks oxidized separately – Glycerol pathway – Fatty acid pathway © 2013 Pearson Education, Inc. Lipid Metabolism: Glycerol • Glycerol glyceraldehyde 3-phosphate (same as in glycolysis) – Enters Krebs cycle – ATP yield ~½ that of glucose 15 ATP/glycerol © 2013 Pearson Education, Inc. Lipid Metabolism: Fatty Acids • Fatty acids undergo beta oxidation in mitochondria – Fatty acid chains broken two-carbon acetic acid fragments and reduced coenzymes • Acetic acid acetyl CoA Krebs cycle • Reduced coenzymes electron transport chain © 2013 Pearson Education, Inc. Lipogenesis • Dietary glycerol and fatty acids not needed for energy stored triglycerides • Triglyceride synthesis (lipogenesis) occurs when cellular ATP and glucose levels high © 2013 Pearson Education, Inc. Lipolysis • Reverse of lipogenesis – Stored fat glycerol and fatty acids for fuel • Preferred by liver, cardiac muscle, resting skeletal muscle © 2013 Pearson Education, Inc. Synthesis of Structural Materials • Phospholipids for cell membranes and myelin • Cholesterol for cell membranes and steroid hormone synthesis • In liver – Synthesis of transport lipoproteins for cholesterol and fats – Synthesis of cholesterol from acetyl CoA – Use of cholesterol to form bile salts © 2013 Pearson Education, Inc.