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Transcript
Chapter 2 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes. Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The Chemistry of Life • Atoms, Ions and Molecules • Water and Mixtures • Energy and Chemical Reactions • Organic compounds Atoms, Ions and Molecules • • • • • The chemical elements Atomic structure Isotopes and radioactivity Ions, electrolytes and free radicals Molecules and chemical bonds The Chemical Elements • Element = simplest form of matter with unique chemical properties • Atomic number = # of protons in nucleus – periodic table • elements arranged by atomic number – 24 elements have biological role • 6 elements = 98.5% of body weight • trace elements in minute amounts Minerals • Inorganic elements absorbed from soil by plants • Equals 40% of body weight – structure (teeth, bones, etc) – enzymes Structure of an Atom • Nucleus = center of atom – protons: single (+) charge, mass = 1 amu – neutrons: no charge, mass = 1 amu • Electron shells surround the nucleus – electrons: single negative charge, little mass – valence electrons in the outermost shell • interact with other atoms • determine chemical behavior Planetary Models of Elements p+ represents protons, no represents neutrons Isotopes and Radioactivity • Isotopes – differ in # of neutrons – extra neutrons increase atomic weight – isotopes of an element are chemically similar • have same valence electrons • Atomic weight – average atomic mass of the isotopes • Carbon Isotopes • Contain the same number of protons and different number of neutrons Radioisotopes and Radioactivity • Isotopes – same chemical behavior, differ in physical behavior – breakdown gives off radiation • Radioisotopes – unstable isotopes – every element has at least one radioisotope • Radioactivity – radioisotopes decay to stable isotopes releasing radiation – we are all mildly radioactive Marie Curie • First woman in world to receive a Ph.D. • First woman to receive Nobel Prize (1903) – discovered radioactivity of radium – trained physicians in use of X rays and radiation therapy as cancer treatment • Died of radiation poisoning at 67 Ions and Ionization • Ions - carry a charge due to an unequal number of protons and electrons • An ion is a charged atom • Ionization = transfer of electrons from one atom to another • Forms an ionic bond • ( stability of valence shell) Anions and Cations • Anion – atom that gained electrons (net negative charge) • Cation – atom that lost an electron (net positive charge) • Ions with opposite charges are attracted to each other Anions and Cations Electrolytes • Salts that ionize in water to form body fluids – capable of conducting electricity • Electrolyte importance – chemical reactivity – osmotic effects (influence water movement) – electrical effects on nerve and muscle tissue • Imbalances cause muscle cramps, brittle bones, coma and death Free Radicals • Particle 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 diet (vitamin E, carotenoids, vitamin C) Molecules and Chemical Bonds • Molecules – two or more atoms covalently bonded • Compounds – two or more atoms of different elements covalently bonded • Molecular formula – elements and how many atoms of each • Structural formula – location of each atom – structural isomers revealed Water Molecule Structural Formula Molecular Compound H20 Chemical Bonds • Ionic bonds • Covalent bonds • Hydrogen bonds • Van der Waals force Ionic Bonds • Attraction of oppositely charged ions • No sharing of electrons • Weak bond (easily dissociates in water) Covalent Bonds • Formed by sharing of valence electrons • Types of covalent bonds – single = sharing of single pair electrons – double = sharing of 2 pairs – nonpolar • shared electrons (equal time around each nucleus) • strongest of all bonds – polar • negative charge where electrons spend most time Single Covalent Nonpolar Covalent Double Covalent Polar Covalent Single Covalent Bond • One pair of electrons are shared Double covalent bonds: Two pairs of electrons are shared each C=O bond Nonpolar /Polar Covalent Bonds electrons shared equally electrons shared unequally Hydrogen Bonds • Weakest bond = no sharing of electrons • Attraction between polar molecules – positive hydrogen atoms to negative oxygen atoms in a 2nd molecule • Physiological importance – properties of water created by shapes of large complex molecules – determined by folding due to hydrogen bonds Hydrogen Bonding in Water Van der Waals Forces • Weak attractions between neutral atoms • Fluctuations in electron density create polarity • Only 1% as strong as a covalent bond – folding of large molecules – significant when 2 large surfaces meet Mixtures and Water • Substances physically but not chemically combined • Mixtures in our bodies contain water • Water 50-75% of body weight – depends on age, sex, percentage body fat, etc. Solvency • Solvency - ability to dissolve other chemicals – Hydrophilic (charged substances) dissolve easily in water – Hydrophobic (neutral substances) do not easily dissolve in water • Water = universal solvent – metabolic reactions and transport of substances Hydrophilic & Hydrophobic Water as a Solvent • Polar water molecules overpower the ionic bond in Na+Cl– forming hydration spheres around each ion – water molecules: negative pole faces Na+, positive pole faces Cl- Adhesion and Cohesion • Adhesion – tendency of one substance to cling to another • Cohesion – tendency of like molecules to cling to each other – water is very cohesive due to its hydrogen bonds – surface film on water formed by surface tension Thermal Stability of Water • Water stabilizes internal temperature – has high heat capacity • hydrogen bonds inhibit temperature increases by inhibiting molecular motion – water absorbs heat without changing temperature – effective coolant • 1 ml of perspiration removes 500 calories – calorie: amount of heat required to raise temperature of 1g of water by 1°C Solutions • Mixture of a solute into a solvent • Small solute particles – pass through cell membranes • Solution transparent • Remains mixed Colloids • Mixture of protein and water – change from liquid to gel state within and between cells • Particles too large to pass through cell membranes • Cloudy • Remains mixed Suspensions and Emulsions • Suspension – particles suspended in a solvent – particles exceed 100nm • too large to pass through a cell membrane – cloudy or opaque appearance – separates on standing • Emulsion – suspension of one liquid in another – fat in breast milk Acids, Bases and pH • An acid is proton donor (releases H+ ions) • A base is proton acceptor (accepts H+ ions) • pH = the concentration of H+ ions in solution – a pH of less than 7 is acidic solution – a pH of greater than 7 is basic solution – a pH of 7.0 is neutral pH pH • pH = measurement of molarity of H+ [H+] on a logarithmic scale – 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 • Our body uses buffers to prevent change – pH of blood ranges from 7.35 to 7.45 – tremors, paralysis or even death pH Scale Work and Energy • Energy - capacity to do work • Kinetic energy - energy of motion – heat is kinetic energy of molecular motion • Potential energy- energy due to object’s position (ions on one side only of cell membrane) – chemical energy - potential energy stored in the molecular bonds Chemical Reaction • Process that forms or breaks an ionic or covalent bond • Symbolized by chemical equation – reactants products Classes of reactions • Decomposition reactions • Synthesis reactions • Exchange reactions Decomposition Reactions • Large molecules broken down into smaller ones • AB A + B Synthesis Reactions • Two or more small molecules combine to form a larger one • A + B AB Exchange Reactions • Two molecules collide and exchange atoms or group of atoms • AB+CD ABCD AC + BD Stomach acid (HCl) and sodium bicarbonate (NaHCO3) from the pancreas combine to form NaCl and H2CO3. Reversible Reactions • Go in either direction (symbolized with double-headed arrow) • CO2 + H2O H2CO3 HCO3- + H+ – most common equation discussed in this book • Law of mass action determines direction – side of equation with greater quantity of reactants dominates Reaction Rates • Basis for reactions is molecular motion and collisions – reactions occur when molecules collide with enough force and the correct orientation • Reaction Rates affected by: – concentration • more concentrated, more collisions, faster rate – temperature • higher temperature, greater collision force, faster rate – Catalysts (enzymes) • speed up reactions without permanent change to itself • holds reactant molecules in correct orientation Metabolism • The sum of ll 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 Oxidation-Reduction Reactions • Oxidation – molecule gives up electrons and releases energy – accepting molecule is the oxidizing agent • oxygen is often the electron acceptor • Reduction – molecule gains electrons and energy – donating molecule is the reducing agent • Oxidation-reduction (redox) reactions – Electrons are often transferred as hydrogen atoms Organic Chemistry • Study of compounds containing carbon • 4 categories of carbon compounds – carbohydrates – lipids – proteins – nucleotides and nucleic acids Organic Molecules and Carbon • Only 4 valence electrons – bonds readily to gain more valence electrons • Forms long chains, branched molecules and rings – serve as the backbone for organic molecules • Carries a variety of functional groups Functional Groups • Atoms attached to carbon backbone • Determines chemical properties Monomers and Polymers • Macromolecules = very large molecules • Polymers = macromolecules formed from monomers bonded together • Monomers = an identical or similar subunit Polymerization • Bonding of monomers together to form a polymer • Formed by dehydration synthesis – starch molecules are a polymer of 3000 glucose monomers – protein molecules are a polymer of amino acids Dehydration Synthesis • Monomers covalently bond together to form a polymer with the removal of a water molecule – A hydroxyl group is removed from one monomer and a hydrogen from the next Hydrolysis • Splitting a polymer (lysis) by the addition of a water molecule (hydro) – a covalent bond is broken • All digestion reactions consists of hydrolysis reactions Organic Molecules: Carbohydrates • Hydrophilic organic molecule • General formula – (CH2O)n n = number of carbon atoms – for glucose, n = 6, so formula is C6H12O6 – 2:1 ratio of hydrogen to oxygen • Names of carbohydrates – word root sacchar- or the suffix -ose often used • monosaccharide or glucose Monosaccharides • Simple sugars • General formula is C6H12O6 – structural isomers • Major monosaccharides – glucose, galactose and fructose – produced by digestion of complex carbohydrates • glucose is blood sugar Disaccharides • Sugar molecule composed of 2 monosaccharides • Major disaccharides – sucrose = table sugar • glucose + fructose – Lactose = sugar in milk • glucose + galactose – Maltose = grain products • glucose + glucose Polysaccharides • Chains of glucose subunits • Starch: energy storage in plants – digestible by humans for energy • Cellulose: structural molecule of plant cell walls – fiber in our diet • Glycogen: energy storage in animals – liver synthesizes after a meal and breaks down between meals Carbohydrate Functions • All digested carbohydrates converted to glucose and oxidized to make ATP • Conjugated carbohydrate = bound to lipid or protein – glycolipids • external surface of cell membrane – glycoproteins • external surface of cell membrane • mucus of respiratory and digestive tracts – proteoglycans • gels that hold cells and tissues together • joint lubrication • rubbery texture of cartilage Organic Molecules: Lipids • Hydrophobic organic molecule – composed of carbon, hydrogen and oxygen • Less oxidized and thus has more calories/grams • Five primary types in humans – fatty acids – triglycerides – phospholipids – eicosanoids – steroids Fatty Acids • Chain of 4 to 24 carbon atoms – carboxyl (acid) group on one end, methyl group on the other and hydrogen bonded along the sides • Classified – saturated - carbon atoms saturated with hydrogen – unsaturated - contains C=C bonds without hydrogen Triglycerides (Neutral Fats) • 3 fatty acids bonded to glycerol molecule (dehydration synthesis) • Function - energy storage, insulation and shock absorption Phospholipids • Triglyceride with one fatty acid replaced by a phosphate group • Amphiphilic character – fatty acid “tails” are hydrophobic – Phosphate “head” is hydrophilic Eicosanoids • Derived from arachidonic acid (a fatty acid) • Hormone-like chemical signals between cells • Includes prostaglandins – produced in all tissues – role in inflammation, blood clotting, hormone action, labor contractions, blood vessel diameter Steroids and Cholesterol • Steroid = lipid with carbon atoms in four rings – all steroids are derived from cholesterol • cortisol, progesterone, estrogens, testosterone and bile acids • Cholesterol – important component of cell membranes – produced only in animal liver cells • naturally produced by our body Organic Molecules: Proteins • Protein = polymer of amino acids • Combination determines structure and function • Amino acid = carbon with 3 attachments – Amino (NH2), carboxy (COOH) and radical group (R group) • 20 unique amino acids – -R groups differ – properties determined by -R group Protein Structure and Shape • Primary structure – amino acid sequence • Secondary structure – coiled or folded shape – hydrogen bonds between negative C=O and positive NH groups • Tertiary structure – further folding and bending into globular and fibrous shapes • Quaternary structure – associations of two or more separate polypeptide chains Protein Conformation and Denaturation • Conformation – unique 3-D shape crucial to function – ability to reversibly change their conformation • opening and closing of cell membrane pores • Denaturation – conformational change that destroys function • extreme heat or pH Protein Functions • Structure – collagen, keratin • Communication – some hormones, cell receptors • Membrane Transport – channels, carriers • Catalysis – enzymes Protein Functions • Recognition and protection – antigens, antibodies and clotting proteins • Movement – molecular motor = molecules that can change shape repeatedly • Cell adhesion – proteins bind cells together Enzymes • Proteins as biological catalysts – promote rapid reaction rates • 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 Enzymes – Enzymes are organic catalysts generally consisting of proteins – Catalysts are molecules that speed up reactions by lowering energies of activation Enzymes and Activation Energy Steps of an Enzyme Reaction • Substrate approaches enzyme molecule • Substrate binds to active site forming enzyme-substrate complex – highly specific • Enzyme breaks bonds in substrate • Reaction products released • Enzyme repeats process over and over Enzymatic Reaction Steps Enzymatic Action • Reusability of enzymes – enzymes are unchanged by the reactions • Astonishing speed – millions of molecules per minute • Temperature and pH – change shape of enzyme and alter its ability to bind – 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 Cofactors and Coenzymes • Cofactors – nonprotein partners (iron, copper, zinc, magnesium or calcium ions) – bind to enzyme and change its shape – essential to function • Coenzymes – organic cofactors derived from water-soluble vitamins (niacin, riboflavin) – transfer electrons between enzymes Coenzyme + NAD • NAD+ transports electrons from one metabolic pathway to another Organic Molecules: Nucleotides • 3 components – nitrogenous base – sugar (monosaccharide) – one or more phosphate groups • Physiological important nucleotides – ATP = energy carrying molecule – cAMP = activates metabolic pathways – DNA = carries genetic code – RNA = assists with protein synthesis ATP (Adenosine Triphosphate) ATP contains adenine, ribose and 3 phosphate groups ATP • Holds energy in covalent bonds – 2nd and 3rd phosphate groups have high energy bonds ~ • ATPases hydrolyze the 3rd high energy phosphate bond – separates into ADP + Pi + energy • Phosphorylation – addition of free phosphate group to another molecule Overview of ATP Production • ATP consumed within 60 seconds • Continually replenished Other Nucleotides • Cyclic adenosine monophosphate (cAMP) – formed by removal of both high energy Pi’s from ATP – formation triggered by hormone binding to cell surface – cAMP becomes “second messenger” within cell – activates effects inside cell Nucleic Acids • DNA (deoxyribonucleic acid) – 100 million to 1 billion nucleotides long – contains genetic code • cell division, sexual reproduction, protein synthesis • RNA (ribonucleic acid) – 3 types – transfer RNA, messenger RNA, ribosomal RNA – 70 to 10,000 nucleotides long – involved in protein synthesis coded for by DNA