Nutrition, Metabolism, and Body Temperature Regulation: Part A

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1 Nutrition, Metabolism, and Body Temperature Regulation: Part A
24 Nutrition, Metabolism, and Body Temperature Regulation: Part A

2 Nutrition Nutrient: a substance in food that promotes normal growth, maintenance, and repair Major nutrients Carbohydrates, lipids, and proteins Other nutrients Vitamins and minerals (and, technically speaking, water)

3 (a) USDA food guide pyramid
Grains Vegetables Fruits Oils Milk Meat and beans (a) USDA food guide pyramid Figure 24.1a

4 potatoes, pasta, sweets: use sparingly
Red meat, butter: use sparingly White rice, white bread, potatoes, pasta, sweets: use sparingly Dairy or calcium supplement: 1–2 servings Fish, poultry, eggs: 0–2 servings Nuts, legumes: 1–3 servings Vegetables in abundance Fruits: 2–3 servings Whole-grain foods at most meals Plant oils at most meals Daily excercise and weight control (b) Healthy eating pyramid Figure 24.1b

5 Carbohydrates Dietary sources
Starch (complex carbohydrates) in grains and vegetables Sugars in fruits, sugarcane, sugar beets, honey and milk Insoluble fiber: cellulose in vegetables; provides roughage Soluble fiber: pectin in apples and citrus fruits; reduces blood cholesterol levels

6 Carbohydrates Uses Glucose is the fuel used by cells to make ATP
Neurons and RBCs rely almost entirely upon glucose Excess glucose is converted to glycogen or fat and stored

7 Carbohydrates Dietary requirements
Minimum 100 g/day to maintain adequate blood glucose levels Recommended minimum 130 g/day Recommended intake: 45–65% of total calorie intake; mostly complex carbohydrates

8 Lipids Dietary sources Triglycerides
Saturated fats in meat, dairy foods, and tropical oils Unsaturated fats in seeds, nuts, olive oil, and most vegetable oils Cholesterol in egg yolk, meats, organ meats, shellfish, and milk products

9 Lipids Essential fatty acids
Linoleic and linolenic acid, found in most vegetable oils Must be ingested

10 Essential uses of lipids in the body
Help absorb fat-soluble vitamins Major fuel of hepatocytes and skeletal muscle Phospholipids are essential in myelin sheaths and all cell membranes

11 Functions of fatty deposits (adipose tissue)
Lipids Functions of fatty deposits (adipose tissue) Protective cushions around body organs Insulating layer beneath the skin Concentrated source of energy

12 Regulatory functions of prostaglandins
Lipids Regulatory functions of prostaglandins Smooth muscle contraction Control of blood pressure Inflammation Functions of cholesterol Stabilizes membranes Precursor of bile salts and steroid hormones

13 Dietary requirements suggested by the American Heart Association
Lipids Dietary requirements suggested by the American Heart Association Fats should represent 30% or less of total caloric intake Saturated fats should be limited to 10% or less of total fat intake Daily cholesterol intake should be no more than 300 mg

14 Proteins Dietary sources
Eggs, milk, fish, and most meats contain complete proteins Legumes, nuts, and cereals contain incomplete proteins (lack some essential amino acids) Legumes and cereals together contain all essential amino acids

15 Proteins Uses Structural materials: keratin, collagen, elastin, muscle proteins Most functional molecules: enzymes, some hormones

16 Use of amino acids in the body
Proteins Use of amino acids in the body All-or-none rule All amino acids needed must be present for protein synthesis to occur Adequacy of caloric intake Protein will be used as fuel if there is insufficient carbohydrate or fat available

17 Proteins Nitrogen balance
State where the rate of protein synthesis equals the rate of breakdown and loss Positive if synthesis exceeds breakdown (normal in children and tissue repair) Negative if breakdown exceeds synthesis (e.g., stress, burns, infection, or injury)

18 Proteins Hormonal controls
Anabolic hormones (GH, sex hormones) accelerate protein synthesis

19 Tryptophan Methionine (Cysteine) Valine Tryptophan Beans and other legumes Methionine Threonine Valine Phenylalanine (Tyrosine) Total protein needs Threonine Leucine Phenylalanine Isoleucine Leucine Lysine Corn and other grains Isoleucine Histidine (Infants) Lysine Arginine (Infants) (a) Essential amino acids (b) Vegetarian diets providing the eight essential amino acids for humans Figure 24.2

20 Proteins Dietary requirements
Rule of thumb: daily intake of 0.8 g per kg body weight

21 Vitamins Organic compounds Crucial in helping the body use nutrients Most function as coenzymes Vitamins D, some B, and K are synthesized in the body

22 Two types, based on solubility
Vitamins Two types, based on solubility Water-soluble vitamins B complex and C are absorbed with water B12 absorption requires intrinsic factor Not stored in the body

23 Vitamins Fat-soluble vitamins
A, D, E, and K are absorbed with lipid digestion products Stored in the body, except for vitamin K Vitamins A, C, and E act as antioxidants

24 Seven required in moderate amounts:
Minerals Seven required in moderate amounts: Calcium, phosphorus, potassium, sulfur, sodium, chloride, and magnesium Others required in trace amounts Work with nutrients to ensure proper body functioning Uptake and excretion must be balanced to prevent toxic overload

25 Minerals Examples Calcium, phosphorus, and magnesium salts harden bone
Iron is essential for oxygen binding to hemoglobin Iodine is necessary for thyroid hormone synthesis Sodium and chloride are major electrolytes in the blood

26 Metabolism: biochemical reactions inside cells involving nutrients
Two types of reactions Anabolism: synthesis of large molecules from small ones Catabolism: hydrolysis of complex structures to simpler ones

27 Metabolism Cellular respiration: catabolism of food fuels and capture of energy to form ATP in cells Enzymes shift high-energy phosphate groups of ATP to other molecules (phosphorylation) Phosphorylated molecules are activated to perform cellular functions

28 Processing of nutrients
Stages of Metabolism Processing of nutrients Digestion, absorption and transport to tissues Cellular processing (in cytoplasm) Synthesis of lipids, proteins, and glycogen, or Catabolism (glycolysis) into intermediates Oxidative (mitochondrial) breakdown of intermediates into CO2, water, and ATP

29 catabolism of nutrients to form intermediates within tissue cells.
Stage 1 Digestion in GI tract lumen to absorbable forms. Transport via blood to tissue cells. PROTEINS CARBOHYDRATES FATS Amino acids Glucose and other sugars Glycerol Fatty acids Stage 2 Anabolism (incorporation into molecules) and catabolism of nutrients to form intermediates within tissue cells. Proteins Glucose Glycogen Fats NH3 Pyruvic acid Acetyl CoA Stage 3 Oxidative breakdown of products of stage 2 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. Krebs cycle Infrequent CO2 O2 Oxidative phosphorylation (in electron transport chain) H H2O Catabolic reactions Anabolic reactions Figure 24.3

30 Oxidation-Reduction (Redox) Reactions
Oxidation; gain of oxygen or loss of hydrogen Oxidation-reduction (redox) reactions Oxidized substances lose electrons and energy Reduced substances gain electrons and energy

31 Oxidation-Reduction (Redox) Reactions
Coenzymes act as hydrogen (or electron) acceptors Nicotinamide adenine dinucleotide (NAD+) Flavin adenine dinucleotide (FAD)

32 ATP Synthesis Two mechanisms Substrate-level phosphorylation
Oxidative phosphorylation

33 Substrate-Level Phosphorylation
High-energy phosphate groups directly transferred from phosphorylated substrates to ADP Occurs in glycolysis and the Krebs cycle

34 (a) Substrate-level phosphorylation
Catalysis Enzyme Enzyme (a) Substrate-level phosphorylation Figure 24.4a

35 Oxidative Phosphorylation
Chemiosmotic process Couples the movement of substances across a membrane to chemical reactions

36 Oxidative Phosphorylation
In the mitochondria Carried out by electron transport proteins Nutrient energy is used to create H+ gradient across mitochondrial membrane H+ flows through ATP synthase Energy is captured and attaches phosphate groups to ADP

37 Proton pumps (electron transport chain)
High H+ concentration in intermembrane space Membrane Proton pumps (electron transport chain) ATP synthase Energy from food ADP + Low H+ concentration in mitochondrial matrix (b) Oxidative phosphorylation Figure 24.4b

38 Carbohydrate Metabolism
Oxidation of glucose C6H12O6 + 6O2  6H2O + 6CO ATP + heat Glucose is catabolized in three pathways Glycolysis Krebs cycle Electron transport chain and oxidative phosphorylation

39 Chemical energy (high-energy electrons)
Electron transport chain and oxidative phosphorylation Glycolysis Krebs cycle Pyruvic acid Glucose Mitochondrial cristae Mitochondrion Cytosol Via oxidative phosphorylation Via substrate-level phosphorylation During glycolysis, each glucose molecule is broken down into two molecules of pyruvic acid in the cytosol. 1 The pyruvic acid then enters the mitochondrial matrix, where the Krebs cycle decomposes it to CO2. During glycolysis and the Krebs cycle, small amounts of ATP are formed by substrate- level phosphorylation. 2 Energy-rich electrons picked up by coenzymes are transferred to the elec- tron 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. 3 Figure 24.5

40 Glycolysis 10-step pathway Anaerobic Occurs in the cytosol
Glucose  2 pyruvic acid molecules Three major phases Sugar activation Sugar cleavage Sugar oxidation and ATP formation

41 Phases of Glycolysis Sugar activation
Glucose is phosphorylated by 2 ATP to form fructose-1,6-bisphosphate

42 Phases of Glycolysis Sugar cleavage
Fructose-1,6-bisphosphate is split into 3-carbon sugars Dihydroxyacetone phosphate Glyceraldehyde 3-phosphate

43 Sugar oxidation and ATP formation
Phases of Glycolysis Sugar oxidation and ATP formation 3-carbon sugars are oxidized (reducing NAD+) Inorganic phosphate groups (Pi) are attached to each oxidized fragment 4 ATP are formed by substrate-level phosphorylation

44 Carbon atom Phosphate Glucose Phase 1 Sugar Activation Glucose is
Electron trans- port chain and oxidative phosphorylation Glycolysis Krebs cycle Carbon atom Phosphate Glucose Phase 1 Sugar Activation Glucose is activated by phosphorylation and converted to fructose-1, 6-bisphosphate 2 ADP Fructose-1,6- bisphosphate Figure 24.6 (1 of 3)

45 Carbon atom Phosphate Fructose-1,6- bisphosphate Phase 2 Sugar
Electron trans- port chain and oxidative phosphorylation Glycolysis Krebs cycle Carbon atom Phosphate Fructose-1,6- bisphosphate Phase 2 Sugar Cleavage Fructose-1, 6-bisphosphate is cleaved into two 3-carbon fragments Dihydroxyacetone phosphate Glyceraldehyde 3-phosphate Figure 24.6 (2 of 3)

46 Carbon atom Phosphate Dihydroxyacetone phosphate Glyceraldehyde
Glycolysis Electron trans- port chain and oxidative phosphorylation Krebs cycle Carbon atom Phosphate Dihydroxyacetone phosphate Glyceraldehyde 3-phosphate Phase 3 Sugar oxidation and formation of ATP The 3-carbon frag- ments are oxidized (by removal of hydrogen) and 4 ATP molecules are formed 2 NAD+ 4 ADP 2 NADH+H+ 2 Pyruvic acid 2 NADH+H+ 2 NAD+ 2 Lactic acid To Krebs cycle (aerobic pathway) Figure 24.6 (3 of 3)

47 Final products of glycolysis
2 pyruvic acid Converted to lactic acid if O2 not readily available Enter aerobic pathways if O2 is readily available 2 NADH + H+ (reduced NAD+) Net gain of 2 ATP

48 Krebs Cycle Occurs in mitochondrial matrix Fueled by pyruvic acid and fatty acids

49 Krebs Cycle Transitional phase
Each pyruvic acid is converted to acetyl CoA Decarboxylation: removal of 1 C to produce acetic acid and CO2 Oxidation: H+ is removed from acetic acid and picked up by NAD+ Acetic acid + coenzyme A forms acetyl CoA

50 Coenzyme A shuttles acetic acid to an enzyme of the Krebs cycle
Each acetic acid is decarboxylated and oxidized, generating: 3 NADH + H+ 1 FADH2 2 CO2 1 ATP

51 Breakdown products of fats and proteins can also enter the cycle
Krebs Cycle Does not directly use O2 Breakdown products of fats and proteins can also enter the cycle Cycle intermediates may be used as building materials for anabolic reactions PLAY Animation: Krebs Cycle

52 Mitochondrion (matrix)
Cytosol Glycolysis Krebs cycle Electron trans- port chain and oxidative phosphorylation Pyruvic acid from glycolysis NAD+ CO2 Transitional phase NADH+H+ Carbon atom Acetyl CoA Mitochondrion (matrix) Inorganic phosphate Coenzyme A Oxaloacetic acid Citric acid (pickup molecule) NADH+H+ (initial reactant) NAD+ Malic acid Isocitric acid NAD+ Krebs cycle CO2 NADH+H+ Fumaric acid -Ketoglutaric acid CO2 FADH2 NAD+ Succinic acid Succinyl-CoA NADH+H+ FAD GTP GDP + ADP Figure 24.7

53 Electron Transport Chain and Oxidative Phosphorylation
The part of metabolism that directly uses oxygen Chain of proteins bound to metal atoms (cofactors) on inner mitochondrial membrane Substrates NADH + H+ and FADH2 deliver hydrogen atoms

54 Electron Transport Chain and Oxidative Phosphorylation
Hydrogen atoms are split into H+ and electrons Electrons are shuttled along the inner mitochondrial membrane, losing energy at each step Released energy is used to pump H+ into the intermembrane space

55 Electron Transport Chain and Oxidative Phosphorylation
Respiratory enzyme complexes I, III, and IV pump H+ into the intermembrane space H+ diffuses back to the matrix via ATP synthase ATP synthase uses released energy to make ATP PLAY Animation: Electron Transport

56 Intermembrane space Inner mitochondrial membrane Mitochondrial matrix
Electron transport chain and oxidative phosphorylation Glycolysis Krebs cycle Intermembrane space Inner mitochondrial membrane 2 H+ + 1 2 ATP synthase FADH2 FAD NADH + H+ (carrying from food) ADP + NAD+ Mitochondrial matrix Electron Transport Chain Chemiosmosis Electrons are transferred from complex to complex and some of their energy is used to pump protons (H+) into the intermembrane space, creating a proton gradient. ATP synthesis is powered by the flow of H+ back across the inner mitochondrial membrane through ATP synthase. Figure 24.8

57 Electron Transport Chain and Oxidative Phosphorylation
Electrons are delivered to O, forming O– O– attracts H+ to form H2O

58 Figure 24.9 NADH+H+ FADH2 Enzyme Complex II Enzyme Complex I Enzyme
Glycolysis Krebs cycle Electron trans- port chain and oxidative phosphorylation FADH2 Enzyme Complex II Enzyme Complex I Enzyme Free energy relative to O2 (kcal/mol) Complex III Enzyme Complex IV Figure 24.9

59 Electronic Energy Gradient
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

60 Two major parts connected by a rod
ATP Synthase Two major parts connected by a rod Rotor in the inner mitochondrial membrane Knob in the matrix Works like an ion pump in reverse

61 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. The protruding, stationary knob contains three catalytic sites that join inorganic phosphate to ADP to make ATP when the rod is spinning. ADP + Mitochondrial matrix Figure 24.11

62 Mitochondrion Cytosol 2 NADH + H+ Electron shuttle across
mitochondrial membrane 2 NADH + H+ 6 NADH + H+ 2 FADH2 Glycolysis Electron transport chain and oxidative phosphorylation 2 Acetyl CoA Krebs cycle Pyruvic acid Glucose (4 ATP–2 ATP used for activation energy) 10 NADH + H+ x 2.5 ATP 2 FADH2 x 1.5 ATP Net +2 ATP by substrate-level phosphorylation +2 ATP by substrate-level phosphorylation + about 28 ATP by oxidative phosphorylation Maximum ATP yield per glucose About 32 ATP Figure 24.12

63 Glycogenesis and Glycogenolysis
Glycogen formation when glucose supplies exceed need for ATP synthesis Mostly in liver and skeletal muscle Glycogenolysis Glycogen beakdown in response to low blood glucose

64 Cell exterior Blood glucose Hexokinase (all tissue cells) Glucose-6- phosphatase (present in liver, kidney, and intestinal cells) ADP Glucose-6-phosphate Glycogenolysis Glycogenesis Mutase Mutase Glucose-1-phosphate Pyrophosphorylase Glycogen phosphorylase Uridine diphosphate glucose Cell interior Glycogen synthase 2 Glycogen Figure 24.13

65 Gluconeogenesis Glucose formation from noncarbohydrate (glycerol and amino acid) molecules Mainly in the liver Protects against damaging effects of hypoglycemia

66 Lipid Metabolism Fat catabolism yields 9 kcal per gram (vs 4 kcal per gram of carbohydrate or protein) Most products of fat digestion are transported as chylomicrons and are hydrolyzed by endothelial enzymes into fatty acids and glycerol

67 Only triglycerides are routinely oxidized for energy
Lipid Metabolism Only triglycerides are routinely oxidized for energy The two building blocks are oxidized separately Glycerol pathway Fatty acid pathway

68 Glycerol is converted to glyceraldehyde phosphate
Lipid Metabolism Glycerol is converted to glyceraldehyde phosphate Enters the Krebs cycle Equivalent to 1/2 glucose

69 Fatty acids undergo beta oxidation, which produces
Lipid Metabolism 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

70 (a glycolysis intermediate)
Lipids Lipase Glycerol Fatty acids H2O Coenzyme A Glyceraldehyde phosphate (a glycolysis intermediate) NAD+ NADH + H+ b Oxidation in the mito- chondria Glycolysis FAD Pyruvic acid FADH2 Cleavage enzyme snips off 2C fragments Acetyl CoA Krebs cycle Figure 24.14

71 Glucose is easily converted into fat because acetyl CoA is
Lipogenesis Triglyceride synthesis occurs when cellular ATP and glucose levels are high Glucose is easily converted into fat because acetyl CoA is An intermediate in glucose catabolism A starting point for fatty acid synthesis

72 The reverse of lipogenesis
Lipolysis The reverse of lipogenesis Oxaloacetic acid is necessary for complete oxidation of fat Without it, acetyl CoA is converted by ketogenesis in the liver into ketone bodies (ketones)

73 Ketogenesis (in liver) Acetyl CoA bodies CO2 + H2O +
Glycolysis Glucose Stored fats in adipose tissue Glycerol Glyceraldehyde phosphate Triglycerides (neutral fats) Lipogenesis Dietary fats Fatty acids Pyruvic acid Certain amino acids b Ketone Ketogenesis (in liver) Acetyl CoA bodies CO2 + H2O + Steroids Electron transport Cholesterol Bile salts Krebs cycle Catabolic reactions Anabolic reactions Figure 24.15

74 Synthesis of Structural Materials
Phospholipids for cell membranes and myelin Cholesterol for cell membranes and steroid hormone synthesis In the liver Synthesis of transport lipoproteins for cholesterol and fats Synthesis of cholesterol from acetyl CoA Use of cholesterol to form bile salts