Chapter 25 Nutrition, Metabolism & Temperature Regulation I. Nutrition: a. Is the process by which certain components of food are obtained & used by the body. b. The process includes: 1. digestion 2. absorption 3. transportation 4. cell metabolism A. Nutrients: A. Are the chemicals taken into the body that are used to produce energy, provide building blocks for new molecules, or function in other chemical reactions. B. They are divided into 6 classes: 1. carbohydrates 2. proteins organic nutrients 3. lipids 4. vitamins 5. minerals taken into body w/o being digested 6. water C. Essential nutrients- are nutrients that must be ingested because the body cannot manufacture them or is unable to manufacture adequate amounts of them. i. Include- certain amino acids, certain fatty acids, most vitamins, minerals, water & a minimum amount of carbohydrates. ii. U.S. Dept of Agriculture provides a food guide pyramid iii. Figure 25.1
B. Kilocalories: 1. a calorie is the amount of energy (heat) necessary to raise the temperature of 1g of water 1 C i. Kilocalorie is 1000 calories & is used to express the larger amounts of energy supplied by foods & released through metabolism. ii. Almost all of the kilocalories supplied by food come from carbohydrates, proteins or fats. iii. 1g of carbohydrates= ~4 kcal of energy & fats= ~ 9 kcal/g C. Carbohydrates: 1. Include monosaccharides, disaccharides & polysaccharides 2. Most common monosaccharides in the diet are glucose & fructose. a. Fructose & galactose are isomers of glucose b. Glucose is in vegetables; fructose is in fruits, berries, honey; glucose is in milk. 3. Disaccharide sucrose table sugar. i. it is a glucose & fructose molecule joined together its principal source is: a. sugarcane b. sugar beets c. maple sugar d. honey 4. Maltose (malt sugar) is derived from germinating cereals 5. lactose-milk 6. complex carbohydrates are polysaccharides a. starch- energy storage molecule in plants b. glycogen- energy storage molecule in animals c. cellulose- forms cell walls I. Uses in the Body: 1. During digestive, polysaccharides & disaccharides are split into monosaccharides & absorbed into the blood. a. humans unable to digest cellulose 2. body uses glucose to produce ATP s a. brain relies almost entirely on glucose b. excess is converted into glycogen & stored in the muscle & liver 3. functions of sugar: a. energy b. form part of DNA, RNA & ATP molecules II. Recommended Amounts: 1. 60% of daily intake of kilocalories be from carbohydrates a. too few carbs /day results in overuse of proteins & fats for energy i. overuse of proteins breaks down muscle ii. overuse of fats results in acidosis iii. excess sugar intake results in obesity & tooth decay D. Lipids: I. Sources in the Diet A. ~95% are triglycerides, which consist of 3 fatty acids attached tot a glycerol molecule & are referred to as fats. 2
II. III. i. Saturated Fats- have only single covalent bonds between the carbon atoms of their fatty acids (in meats, dairy products, eggs, coconut oil & palm oil). ii. Unsaturated Fats- have one or more double covalent bonds between the carbon atoms. a. monosaturated include oil & peanut oil b. polyunsaturated- occur in fish, safflower, sunflower corn oil. B. the remaining 5% include cholesterol & phospholipids like lecithin (in egg yolks) Uses in the Body: 1. a gram of triglyceride delivers more than 2X as many kilocalories as a gram of carbohydrate. 2. excess triglycerides are stored in adipose tissue or the liver a. adipose tissue surrounds & pads organs b. insulator under the skin Recommended Amounts: 1. American Heart Association recommends that fat account for 30% r less of the total daily kilocalorie intake; with 8-10% coming from saturated fats; ~15% from monounsaturated fats. 2. cholesterol limited to 300mg or less/day (1 egg yolk) 3. Excess amounts of fats contribute to cardiovascular disease. a. High-fat intake is associated with colon cancer. 4. Linoleic acid & α-linolenic acid are essential fatty acids because the body cannot synthesize them & they must be ingested (in plant oils-canola & soybean oils) E. Proteins: I. Sources in the Diet: 1. Are chains of amino acids; they are conducted of 20 different kinds of amino acids, which are divided into 2 group: essential & non essential. a. Essential (body cannot synthesize): 1. histamine 2. isoleucine 3. leucine 4. lysine 5. methionine 6. phenylalanine 7. threonine 8. tryptophan 9. valine 2. complete proteins are: meat, fish, poultry, milk, cheese & eggs 3. incomplete proteins are: leafy green vegetables, grains & legumes (peas & beans) II. Uses in the Body: 1. Essential & non essential amino acids are used to synthesize proteins. 3
III. F. Vitamins: a. Collagen- structural strength b. Enzymes- regulate the rate of chemical reaction c. Hormones- regulate physiological processes d. Proteins in blood- act as buffers w/ ph changes e. Hemoglobin- transports O2 & CO2 f. Proteins also function as carrier molecules g. Energy source Recommended Amounts: 1. Adult-.8g/kg of body weight or 55g protein/day for a 2,000 kcal/day intake. 2. Nitrogen balance- means that the nitrogen content excreted in the urine & feces. 1. Are organic molecules that exist in minute quantities in food and are essential to normal metabolism. a. Essential vitamin- cannot be produced by the body & must be obtained through the diet. b. Provitamin- is a part of a vitamin that can be assembled or modified by the body into a functional vitamin. (ex. Beta carotene) i. The other provitimains are: 1. 7-dehydrocholesterol- which can be converted to vitamin D. 2. Tryptophan- can be converted to niacin. 2. Vitamins are not broken down catabolism, but are used in their original or modified forms. a. Chemical structure is destroyed by heat. 3. Many vitamins function as coenzymes, which combine with enzymes to make the enzymes functional. a. B2 (biotin) & B3 (pantothenic acid) are critical for the chemical reactions necessary to produce energy. b. Folate & B12 are involved in nucleic acid synthesis. c. Vitamin A, B1, B6, B12, C & D are necessary for growth. d. Vitamin K- involved in blood clotting 4. Vitamins are either fat-soluble or water-soluble a. Fat-soluble- (A,D,G,K) - dissolve in lipids b. Water-soluble- (B&C) - dissolve in water; and remain a short time. 5. Recommended Dietary Allowances (RDA s) - are the nutrient intakes sufficient to meet the needs of nearly all in certain age & gender groups. a. Established for different aged men & women b. Set for pregnant & lactating women c. They establish a minimum intake of vitamins & minerals that should protect almost everyone in a given 4
group from diseases caused by vitamin & mineral deficiencies. 6. Free Radicals & Antioxidants: G. Minerals: 1. Are inorganic nutrient that are necessary for normal metabolic functions. a. Constitute ~4-5% of the total body weight & are components of coenzymes, a few vitamins, hemoglobin & other organic molecules. 2. important functions: a. establishing resting membrane potentials b. generating action potentials c. adding mechanical strength to bones & teeth d. combining with Organic molecules e. Acting as coenzymes, buffers, or regulators of osmotic pressure. 5
3. Table 25.3 H. Daily Values: 4. Minerals are ingested & obtained from animal & plant sources a. Minerals are usually lost in the processing of food & must be added. 1. Are dietary reference values now appearing on food labels to help consumers plan a healthy diet. 2. They are based on 2 reference values: a. Reference Daily Intakes (RDI s)- are set for 4 categories of people: i. Infants ii. Toddlers iii. Over the age of 4 iv. Pregnant or lactating women b. Daily Reference Values (DRV s) - are set for total fat, saturated fat, cholesterol, total carbohydrates, dietary fiber, sodium, potassium, & protein. c. RDI s & DRV s are combined to form the Daily Values. (Based on a 2,000 kcal reference diet) 3. Daily Values for energy-producing nutrients are determined as a percentage of daily kcal intakes: 60% for carbs, 20% for total fats, 10% for saturated fats, & 10% for proteins. 6
4. The Daily Value is used to calculate the Percent Daily Value so that the public has useful & accurate dietary information. II. Metabolism: 1. Is the total of all the chemical changes that occur in the body. It consists of: a. Anabolism- the energy- requiring process by which small molecules are joined to form larger molecules (occurs in all cells). b. Catabolism- the energy- releasing process by which large molecules are broken down into small molecules (begins during the process of digestion & concluded with in the cells) 2. Cellular metabolism process is referred to as cellular metabolism or cellular respiration. i. ADP + Pi (phosphate group) + energy ATP (energy) ii. The chemical reactions responsible for the transfer of energy from the chemical bonds of nutrient molecules to ATP molecules involve oxidation- reduction reactions. III. Carbohydrate Metabolism: A. Glycolysis: a. It is a series of chemical reactions in the cytosol that results in the break down of glucose into 2 pyruvic acid molecules. b. Glycolysis has 4 phases: 1. input of ATP (2) a. Phosphate group is transferred from ATP to the glucose molecule (phosphorylation) to form glucose-6-phosphate; the rearranged to form fructose-6-phospahte; then converted to fructose-1, 6 bisphosphate by addition of another phosphate group. 2. Sugar cleavage- fructose 1, 6 bisphosphate is closed into (2) 3-carbon molecules (glyceraldehyde-3-phosphate & dihydroxyacetone phosphate); dihydroxyacetone phosphate is rearranged to form (2) glyceraldehyde-3-phosphate. 3. NADH Production each glyceraldehyde is oxidized to form 1, 3- bisphosphoglyceric acid & NAD+ is reduced to NADH (it is the carrier molecule with 2 high energy electrons that can be used to produce ATP molecules through the electron-transport chain. 4. ATP & pyruvic acid production- last 4 steps of Glycolysis produce 2-ATP molecules & 1-pyruvic acid molecule from each 1, 3-bisphosphoglyceric acid molecule. B. Anaerobic Respiration: 1. Is the break down of glucose in the absence of oxygen to produce (2) molecules of lactic acid & (2) molecules of ATP. 7
C. Aerobic Respiration: 2. (2) Phases: a. Glycolysis- several reactions produce (2) pyruvic acid molecules & (2) NADH. b. Lactic acid formation- conversion of pyruvic acid to lactic acid. i. The process of converting lactic acid to glucose is Cori Cycle. ii. The oxygen necessary for the synthesis of the ATP is part of the oxygen debt. 1. Is the break down of glucose in the presence of oxygen to produce CO2, water & 38 ATP molecules. a. Most of the ATP molecules to sustain life are through aerobic respiration (4 phases): I. Glycolysis II. Acetyl-CoA Formation i. Pyruvic acid moves from the cytosol into a mitochondrion; enzymes remove a carbon & (2) oxygen atoms from pyruvic acid molecule to form the acetyl group combines with CoA to form acetyl-coa. Each (2) pyruvic acid molecules gives (3) acetyl- COA molecules, (2) CO2 molecules & (2) NADH. III. Citric Acid Cycle: i. Named because of the 6-carbon citric acid molecules formed in the 1 st step. ii. Also called the Kreb s Cycle iii. 3 events occur: 1. ATP formation (1) 2. NADH & FADH2 production a. 1 citric acid molecule (3) NADH molecules are converted to NADH & (1) FAD molecule is converted to FADH2 3. Carbon dioxide production IV. Electron Transport Chain: 1. Is a series of electron carriers in the inner mitochondrial membrane. 2. Electrons are transferred from NADH & FADH2 to the electron-transport carriers & hydrogen ions are released from NADH & FADH2. 3. Electrons are carried through a series of oxidation-reduction reactions. a. Without oxygen to accept the electrons, the reactions of the 8
chain cease, stopping aerobic respiration. V. Summary of ATP Production: 1. each glucose molecule through aerobic respiration produces: a. 38 ATP molecules i. 2 from Glycolysis ii. 2 from Kreb (citric acid cycle) iii. 34 from NADH & FADH2 molecules in electron-transport chain I. (1) NADH formed- (3) ATP are produced II. (1) FADH2 molecule- 2 ATP are produced 2. Six CO2 molecules are produced in aerobic respiration 3. Six water molecules are used, but 12 are formed; net gain 6 H2O molecules. VI. Lipid Metabolism: 1. Lipids are the body s main energy storage molecule a. Responsible for ~99% of the body s energy storage & glycogen accounts for ~1%. 2. Lipids are stored primarily as triglycerides in adipose tissue. a. Free fatty acids- fatty acids released into the blood as triglycerides are broken down. 3. The metabolism of fatty acids occurs by beta-oxidation. The chain removes 2 carbon atoms at a time until it is converted into acetyl-coa molecules. a. Acetyl-CoA is also used in ketogenesis, the formation of ketone bodies. i. Acetoacetic acid, β-hydroxybutyric acid, and acetone are called ketone bodies. b. excess ketones: 9
V. Protein Metabolism: 1. Amino acids are used to synthesize needed proteins. They are not stored in the body. 2. The synthesis of non essential amino acids usually begins with keto acids. a. transamination- a reaction in which an amino acid group is transferred from an amino acid to the keto acid. b. most amino acids can undergo transamination to produce glutamic acid. c. Amino acids can be used as a source of energy by oxidative deamination. d. amino acids are also used as a source of energy by converting them into the intermediate molecules of carbohydrate metabolism. VI. Interconversion of Nutrient Molecules: 1. Blood glucose enters most cells by facilitated diffusion & converted to glucose- 6- phosphate; goes through glycolsis to produce ATP. a. Excess glucose is used to form glycogen by glycogenesis. 2. Glucose & amino acids are used to synthesize lipids by lipogenesis. 3. When glucose is needed, glycogen can be broken down into glucose-6-prosphateby a reaction called glycogenolysis. 4. Skeletal muscle cannot convert glucose-6-phosphate to glucose as it does not have the necessary enzymes. 5. Gluconeogensis- is a process when glycogen levels are inadequate to supply glucose; amino acids from proteins & glycerol from triglycerides are used. VII. Metabolic States: I. 2 metabolic states: a. Absorptive state- the period immediately after a meal when nutrients are being absorbed through the intestinal wall into the circulatory & lymphatic system. i. Usually last ~4 hours b. Post absorptive state- occurs last in the morning, late in the afternoon, or during the night after each absorptive state is concluded. i. Normal blood glucose level range between 70-100 mg/100 mil & this is vital to the body s homeostasis. ii. The first source of blood glucose during this state is the glycogen stored in the liver (for~4 hours); once depleted fats are used. VIII. Metabolic Rate: 1. Is the total amount of energy produced and used by the body per unit of time. 2. It is usually estimated by measuring the amount of oxygen used per minute because most ATP production involves the use of oxygen. 3. metabolic energy is used in (3) ways: I. Basal Metabolic Rate: a. Is the metabolic rate calculated in expended kilocalories per square meter of body surface area per hour. b. BMR is the energy needed to keep the resting body functional. It accounts for ~60% of energy expenditure. c. It supports: 1. Active-transport mechanism 2. Muscle tone 10
3. Maintenance of body temperature 4. Beating of the heart d. factors that affect BMR: 1. muscle tissue 2. age 3. fever 4. dieting or fasting 5. thyroid hormones 6. males or females 7. pregnancy II. Thermic Effect of Food: a. Is the energy cost of food ingestion, notability increase of digestive tract, increase in active-transport, & synthesis of new molecules by the liver. III. Muscular Activity: 1. It consumes ~30% of the body s energy. 2. Energy loss through muscular activity is the only component of energy expenditure that a person can reasonably control. IX. Body Temperature Regulation: 1. Humans are hemeotherms or warm-blooded animals & ca regulate body temperature rather than have it adjusted by the external environment. 2. Free energy is the total amount of energy liberated by the complete catabolism of food. a. Usually expressed in terms of kcal per molecule consumed. 3. average temperature i. 37 C (98.6 F) orally ii. 37.6 C (99.7 F) rectally (more accurate) 4. heat can be exchanged with the environment in a number of ways: a. radiation- loss of heat as infrared radiation; type of electromagnetic radiation b. Conduction- the exchange of heat between objects in direct content with each other. c. Convection- transfer of heat between the body & the air. d. Evaporation- the conversion of water from a liquid to a gaseous form (requires heat) 11
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