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Transcript
Chapter 2 *Lecture PowerPoint The Chemistry of Life *See separate FlexArt PowerPoint slides for all figures and tables preinserted into PowerPoint without notes. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Introduction • A little knowledge of chemistry can help you choose a healthy diet, use medications more wisely, avoid worthless health fads and frauds, and explain treatments and procedures to your patients or clients. 2-2 The Chemical Elements • Element—simplest form of matter to have unique chemical properties • Atomic number of an element—number of protons in its nucleus – Periodic table • Elements arranged by atomic number • Elements represented by one- or two-letter symbols – 24 elements have biological role • 6 elements = 98.5% of body weight – Oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus • Trace elements in minute amounts, but play vital roles 2-3 The Chemical Elements 2-4 The Chemical Elements • Minerals—inorganic elements extracted from soil by plants and passed up the food chain to humans – Ca, P, Cl, Mg, K, Na, Fe, Zn, and S • Constitute about 4% of body weight – Structure (teeth, bones, etc.) – Enzymes • Electrolytes needed for nerve and muscle function are mineral salts 2-5 Bohr Planetary Models of Elements Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. First energy level Nitrogen (N) 7p+, 7e-, 7n0 Atomic number = 7 Atomic mass = 14 Second energy level Nitrogen (N) 7p+, 7e-, 7n0 Atomic number = 7 Atomic mass = 14 Third energy level Sodium (Na) 11p+, 11e-, 12n0 Atomic number = 11 Atomic mass = 23 Fourth energy level Potassium (K) 19p+, 19e-, 20n0 Atomic number = 19 Atomic mass = 39 Figure 2.1 p+ represents protons, n0 represents neutrons 2-6 Isotopes and Radioactivity • Isotopes—varieties of an element that differ from one another only in the number of neutrons and therefore in atomic mass – Extra neutrons increase atomic weight – Isotopes of an element are chemically similar • Have same valence electrons • Atomic weight (relative atomic mass) of an element accounts for the fact that an element is a mixture of isotopes 2-7 Isotopes and Radioactivity • Radioisotopes – Unstable isotopes that give off radiation – Every element has at least one radioisotope • Radioactivity – Radioisotopes decay to stable isotopes releasing radiation – We are all mildly radioactive 2-8 Radiation and Madame Curie • First woman to receive Nobel Prize (1903) • First woman in world to receive a Ph.D. – Coined term radioactivity – Discovered radioactivity of polonium and radium – Trained physicians in use of X-rays and pioneered radiation therapy as cancer treatment • Died of radiation poisoning at 67 Figure 2.3 2-9 Isotopes and Radioactivity • particle (dangerous if inside the body) – 2 protons + 2 neutrons; cannot penetrate skin • particle (dangerous if inside the body) – free electron; penetrates skin a few millimeters • particle (emitted from uranium and plutonium) – penetrating; very dangerous gamma rays 2-10 Isotopes and Radioactivity • Physical half-life of radioisotopes – Time needed for 50% to decay into a stable state – Nuclear power plants create radioisotopes • Biological half-life of radioisotopes – Time required for 50% to disappear from the body – Decay and physiological clearance 2-11 Ions, Electrolytes, and Free Radicals • Ions—charged particles with unequal number of protons and electron • Elements with one to three valence electrons tend to give up, and those with four to seven electrons tend to gain • Ionization—transfer of electrons from one atom to another ( stability of valence shell) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 11 protons 12 neutrons 11 electrons Sodium atom (Na) 17 protons 18 neutrons 17 electrons Chlorine atom (Cl) 1 Transfer of an electron from a sodium atom to a chlorine atom Figure 2.4 (1) 2-12 Ions, Electrolytes, and Free Radicals • Anion—atom that gains electrons (net negative charge) • Cation—atom that loses an electron (net positive charge) • Ions with opposite charges are attracted to each other Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. – + Figure 2.4 (2) 11 protons 12 neutrons 10 electrons Sodium ion (Na+) 17 protons 18 neutrons 18 electrons Chloride ion (Cl–) Sodium chloride 2 The charged sodium ion (Na+) and chloride ion (Cl–) that result 2-13 Ions, Electrolytes, and Free Radicals • Electrolytes—salts that ionize in water and form solutions capable of conducting an electric current • Electrolyte importance – Chemical reactivity – Osmotic effects (influence water movement) – Electrical effects on nerve and muscle tissue 2-14 Ions, Electrolytes, and Free Radicals • Electrolyte balance is one of the most important considerations in patient care • Imbalances have ranging effects from muscle cramps, brittle bones, to coma and cardiac arrest 2-15 Ions, Electrolytes, and Free Radicals 2-16 Ions, Electrolytes, and Free Radicals • Free radicals—chemical particles with an odd number of electrons • Produced by – Normal metabolic reactions, radiation, chemicals • Causes tissue damage – Reactions that destroy molecules – Causes cancer, death of heart tissue, and aging • Antioxidants – Neutralize free radicals – In body, superoxide dismutase (SOD) converts superoxides into water and oxygen – In diet (selenium, vitamin E, vitamin C, carotenoids) 2-17 Water and Mixtures • Mixtures—consist of substances physically blended, but not chemically combined • Body fluids are complex mixtures of chemicals – Each substance maintains its own chemical properties • Most mixtures in our bodies consist of chemicals dissolved or suspended in water • Water 50% to 75% of body weight – Depends on age, sex, fat content, etc. 2-18 Water • Solvency—ability to dissolve other chemicals • Water is called the universal solvent – Hydrophilic—substances that dissolve in water • Molecules must be polarized or charged – Hydrophobic—substances that do not dissolve in water • Molecules are nonpolar or neutral (fat) • Virtually all metabolic reactions depend on the solvency of water 2-19 Water • Water helps stabilize the internal temperature of the body – Has high heat capacity—the amount of heat required to raise the temperature of 1 g of a substance by 1°C – Calorie (cal)—the amount of heat that raises the temperature of 1 g of water 1°C • Hydrogen bonds inhibit temperature increases by inhibiting molecular motion • Water absorbs heat without changing temperature very much – Effective coolant • 1 mL of perspiration removes 500 calories 2-20 Measures of Concentration • How much solute in a given volume of solution? • Weight per volume – Weight of solute in given volume of solution • IV saline: 8.5 g NaCl per liter of solution • Biological purposes: milligrams per deciliter – mg/dL (deciliter = 100 mL) 2-21 Measures of Concentration • Percentages – Weight/volume of solute in solution • IV D5W (5% w/v dextrose in distilled water) – 5 g dextrose and fill to 100 mL water • Molarity—known number of molecules per volume – Moles of solute/liter of solution – Physiologic effects based on number of molecules in solution not on weight 2-22 Measures of Concentration • Molarity (M) is the number of moles of solute/ liter of solution – MW of glucose is 180 – One-molar (1.0 M) glucose solution contains 180 g/L 2-23 Measures of Concentration • Electrolytes are important for their chemical, physical, and electrical effects on the body – Electrical effects determine nerve, heart, and muscle actions 2-24 Acids, Bases, and pH • An acid is a proton donor (releases H+ ions in water) • A base is a proton acceptor (accepts H+ ions) – Releases OH- ions in water • pH is a measure derived from the molarity of H+ – a pH of 7.0 is neutral pH (H+ = OH-) – a pH of less than 7 is acidic solution (H+ > OH-) – a pH of greater than 7 is basic solution (OH- > H+ ) 2-25 Acids, Bases, and pH • pH—measurement of molarity of H+ [H+] on a logarithmic scale – pH scale invented by Sören Sörensen in 1909 to measure acidity of beer – pH = -log [H+] thus pH = -log [10-3] = 3 • A change of one number on the pH scale represents a 10-fold change in H+ concentration – A solution with pH of 4.0 is 10 times as acidic as one with pH of 5.0 2-26 Acids, Bases, and pH • Our body uses buffers to resist changes in pH – Slight pH disturbances can disrupt physiological functions and alter drug actions – pH of blood ranges from 7.35 to 7.45 – Deviations from this range cause tremors, paralysis, or even death 2-27 Acids, Bases, and pH Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Wine, vinegar (2.4–3.5) Gastric juice (0.9–3.0) Lemon 1M hydrochloric acid(0) Bananas, tomatoes (4.7) Milk, Pure water Egg white saliva (7.0) (8.0) (6.3–6.6) Bread, black coffee (5.0) Household bleach (9.5) Household ammonia (10.5–11.0) Oven cleaner, lye (13.4) 1 M sodium hydroxide (14) juice (2.3) 3 2 4 5 6 7 Neutral 8 9 10 11 12 13 1 0 14 Figure 2.12 2-28 Metabolism, Oxidation, and Reduction • All the chemical reactions of the body • Catabolism – Energy-releasing (exergonic) decomposition reactions • Breaks covalent bonds • Produces smaller molecules • Releases useful energy • Anabolism – Energy-storing (endergonic) synthesis reactions • Requires energy input • Production of protein or fat • Driven by energy that catabolism releases • Catabolism and anabolism are inseparably linked 2-29 Carbon Compounds and Functional Groups • Organic chemistry—the study of compounds containing carbon • Four categories of carbon compounds – – – – Carbohydrates Lipids Proteins Nucleotides and nucleic acids 2-30 Monomers and Polymers • Macromolecules—very large organic molecules – Very high molecular weights • Proteins, DNA • Polymers—molecules made of a repetitive series of identical or similar subunits (monomers) – Starch is a polymer of about 3,000 glucose monomers • Monomers—identical or similar subunits 2-31 Carbohydrates Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glucose • Three important monosaccharides – Glucose, galactose, and fructose – Same molecular formula: C6H12O6 CH2OH O H HO Galactose • Glucose is blood sugar OH H H OH OH CH2OH O HO H • All isomers of each other – Produced by digestion of complex carbohydrates H H H H OH H H OH OH Fructose O HOCH2 H OH H OH HO CH2OH H Figure 2.16 2-32 Carbohydrates Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Disaccharide—sugar molecule composed of two monosaccharides Sucrose • Three important disaccharides Lactose – Sucrose—table sugar CH2OH H OH H • Glucose + galactose – Maltose—grain products • Glucose + glucose CH2OH O H H H O HO H HO CH2OH OH OH CH2OH H H OH OH H O HO H OH H H H H OH O H • Glucose + fructose – Lactose—sugar in milk O H H OH O H CH2OH Maltose CH2OH CH2OH O H H OH H HO H OH H O H O H OH OH H H H Figure 2.17 OH 2-33 Carbohydrates • Oligosaccharides—short chains of 3 or more monosaccharides (at least 10) • Polysaccharides—long chains of monosaccharides (at least 50) 2-34 Carbohydrates • Three polysaccharides of interest in humans – Glycogen: energy storage polysaccharide in animals • Made by cells of liver, muscles, brain, uterus, and vagina • Liver produces glycogen after a meal when glucose level is high, then breaks it down between meals to maintain blood glucose levels • Muscles store glycogen for own energy needs • Uterus uses glycogen to nourish embryo 2-35 Carbohydrates • Three polysaccharides of interest in humans (cont) – Starch: energy storage polysaccharide in plants • Only significant digestible polysaccharide in the human diet – Cellulose: structural molecule of plant cell walls • Fiber in our diet 2-36 Glycogen Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CH2OH CH2OH O O O O CH2OH CH2OH CH2 O O (a) O O O O CH2OH O O O O (b) Figure 2.18 2-37 Carbohydrates 2-38 Lipids • Hydrophobic organic molecule – Composed of carbon, hydrogen, and oxygen – With high ratio of hydrogen to oxygen • Less oxidized than carbohydrates, and thus has more calories/gram • Five primary types in humans – – – – – Fatty acids Triglycerides Phospholipids Eicosanoids Steroids 2-39 Lipids • Triglycerides (Neutral Fats) – Three fatty acids covalently bonded to three-carbon alcohol called glycerol – Each bond formed by dehydration synthesis – Once joined to glycerol, fatty acids can no longer donate protons— neutral fats – Broken down by hydrolysis • Triglycerides at room temperature – When liquid, called oils • Often polyunsaturated fats from plants – When solid, called fat • Saturated fats from animals • Primary function: energy storage, insulation, and shock absorption (adipose tissue) 2-40 Lipids • Similar to neutral fat except that one fatty acid is replaced by a phosphate group Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CH3 CH3 N+ CH3 CH2 CH2 Nitrogencontaining group (choline) O O P O Hydrophilic region (head) Phosphate group O • Structural foundation of cell membrane O CH CH2 O O C C CH CH3 Glycerol O (CH2)5 (CH2)12 • Amphiphilic – Fatty acid “tails” are hydrophobic – Phosphate “head” is hydrophilic CH2 Fatty acid tails CH Hydrophobic region (tails) (CH2)5 CH3 (a) (b) Figure 2.21a,b 2-41 Lipids • Steroid—a lipid with 17 of its carbon atoms in four rings • Cholesterol—the “parent” steroid from which the other steroids are synthesized – Cortisol, progesterone, estrogens, testosterone, and bile acids – Synthesized only by animals • Especially liver cells • 15% from diet, 85% internally synthesized – Important component of cell membranes – Required for proper nervous system function 2-42 “Good” and “Bad” Cholesterol • One kind of cholesterol – Does far more good than harm • “Good” and “bad” cholesterol actually refers to droplets of lipoprotein in the blood – Complexes of cholesterol, fat, phospholipid, and protein • HDL (high-density lipoprotein): “good” cholesterol – Lower ratio of lipid to protein – May help to prevent cardiovascular disease • LDL (low-density lipoprotein): “bad” cholesterol – High ratio of lipid to protein – Contributes to cardiovascular disease 2-43 Cholesterol Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H 3C CH3 CH3 CH3 CH3 HO Figure 2.23 2-44 Lipids and Functions 2-45 Proteins • Greek word meaning “of first importance” – Most versatile molecules in the body • Protein—a polymer of amino acids • Amino acid—central carbon with three attachments – Amino group (NH2), carboxyl group (—COOH), and radical group (R group) • 20 amino acids used to make the proteins are identical except for the radical (R) group – Properties of amino acid determined by R group 2-46 Proteins Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Some nonpolar amino acids Some polar amino acids Methionine H Cysteine H H H N N C H CH2 CH2 S C H CH3 O OH Tyrosine H H H C H N CH2 OH H C O OH Arginine N H SH C C O CH2 C NH2+ (CH2)3 O C NH2 C OH NH Figure 2.24a OH (a) • Amino acids differ only in the R group 2-47 Proteins • Conjugated proteins contain a non–amino acid moiety called a prosthetic group • Hemoglobin contains four complex ironcontaining rings called a heme moiety Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 2.25 (4) Beta chain Alpha chain Association of two or more polypeptide chains with each other Heme groups Alpha chain Quaternary structure Beta chain 2-48 Primary Structure of Insulin Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phe Gly Arg Glu Gly Cys Phe Tyr Glu Asn Tyr Thr Leu Pro lle Lys Tyr Asn Leu Ala Glu Glu Ser Gln Val Cys Cys Leu lle Cys Ser Val Figure 2.26 Gly Tyr Val Leu Phe Leu Cys Gln Thr Val His Thr Ser Asn Gln His Leu Cys Gly 2-49 Proteins • Catalysis – Enzymes • Recognition and protection – Immune recognition – Antibodies – Clotting proteins • Movement – Motor proteins—molecules with the ability to change shape repeatedly • Cell adhesion – Proteins bind cells together – Immune cells to bind to cancer cells – Keeps tissues from falling apart 2-50 Enzymes and Metabolism • Enzymes—proteins that function as biological catalysts – Permit reactions to occur rapidly at normal body temperature • Substrate—substance an enzyme acts upon • Naming convention – Named for substrate with -ase as the suffix • Amylase enzyme digests starch (amylose) • Lowers activation energy—energy needed to get reaction started – Enzymes facilitate molecular interaction 2-51 Enzyme Structure and Action • Substrate approaches active site on enzyme molecule • Substrate binds to active site forming enzyme– substrate complex – Highly specific fit—‟lock and key” • Enzyme–substrate specificity • Enzyme breaks covalent bonds between monomers in substrate 2-52 Enzyme Structure and Action • Factors that change enzyme shape – pH and temperature – Alters or destroys the ability of the enzyme to bind to substrate – Enzymes vary in optimum pH • Salivary amylase works best at pH 7.0 • Pepsin works best at pH 2.0 – Temperature optimum for human enzymes—body temperature (37°C) 2-53 Cofactors • Cofactors – About two-thirds of human enzymes require a nonprotein cofactor – Inorganic partners (iron, copper, zinc, magnesium, and calcium ions) – Some bind to enzyme and induce a change in its shape, which activates the active site – Essential to function 2-54 Cofactors • Coenzymes – Organic cofactors derived from water-soluble vitamins (niacin, riboflavin) – They accept electrons from an enzyme in one metabolic pathway and transfer them to an enzyme in another 2-55 ATP, Other Nucleotides, and Nucleic Acids • Three components of nucleotides – Nitrogenous base (single or double carbon– nitrogen ring) – Sugar (monosaccharide) – One or more phosphate groups • ATP—best-known nucleotide – Adenine (nitrogenous base) – Ribose (sugar) – Phosphate groups (3) 2-56 Adenosine Triphosphate Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Adenine NH2 Adenine NH2 C C N N C N N C CH HC CH C HC N N C N N Adenosine Ribose Ribose Triphosphate –O O O O P O P O P –O –O Monophosphate O CH2 O O –O HO H H OH (a) Adenosine triphosphate (ATP) P CH2 O H H OH O H H O H H OH (b) Cyclic adenosine monophosphate (cAMP) Figure 2.30a, b ATP contains adenine, ribose, and three phosphate groups 2-57 Adenosine Triphosphate • Body’s most important energy-transfer molecule • Briefly stores energy gained from exergonic reactions • Releases it within seconds for physiological work • Holds energy in covalent bonds – Second and third phosphate groups have high energy bonds (~) – Most energy transfers to and from ATP involve adding or removing the third phosphate 2-58 Adenosine Triphosphate • Adenosine triphosphatases (ATPases) hydrolyze the third high-energy phosphate bond – Separates into ADP + Pi + energy • Phosphorylation – Addition of free phosphate group to another molecule – Carried out by enzymes called kinases (phosphokinases) 2-59 Sources and Uses of ATP Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glucose + 6 O2 are converted to 6 CO2 + 6 H2O which releases energy which is used for ADP + Pi ATP which is then available for Figure 2.31 Muscle contraction Ciliary beating Active transport Synthesis reactions etc. 2-60 ATP Production Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis Glucose 2 ADP + 2 Pi Stages of glucose oxidation 2 ATP Pyruvic acid Anaerobic fermentation No oxygen available Lactic acid Aerobic respiration Oxygen available CO2 + H2O Mitochondrion 36 ADP + 36 Pi • ATP consumed within 60 seconds of formation • Entire amount of ATP in the body would support life for less than 1 minute if it were not continually replenished • Cyanide halts ATP synthesis 36 ATP Figure 2.32 2-61 Other Nucleotides • Guanosine triphosphate (GTP) – Another nucleotide involved in energy transfer – Donates phosphate group to other molecules • Cyclic adenosine monophosphate (cAMP) – Nucleotide formed by removal of both second and third phosphate groups from ATP – Formation triggered by hormone binding to cell surface – cAMP becomes “second messenger” within cell – Ativates metabolic effects inside cell 2-62 Nucleic Acids • Polymers of nucleotides • DNA (deoxyribonucleic acid) – 100 million to 1 billion nucleotides long – Constitutes genes • Instructions for synthesizing all of the body’s proteins • Transfers hereditary information from cell to cell and generation to generation • RNA (ribonucleic acid)—three types – – – – Messenger RNA, ribosomal RNA, transfer RNA 70 to 10,000 nucleotides long Carries out genetic instruction for synthesizing proteins Assembles amino acids in the right order to produce proteins 2-63