Bài giảng Biology 25: Human Biology - Chapter 2: Chemicals and the body

Chapter 2 Biology 25: Human BiologyProf. GonsalvesLos Angeles City CollegeLoosely Based on Mader’s Human Biology,7th editionI. Elements: Substances that can not be broken down into simpler substances by chemical reactions.There are 92 naturally occurring elements: Oxygen, carbon, nitrogen, calcium, sodium, etc.Life requires about 25 of the 92 elementsChemical Symbols: Abbreviations for the name of each element.Usually one or two letters of the English or Latin name of the elementFirst letter upper case, second letter lower case. Example: Helium (He), sodium (Na), potassium (K), gold (Au).Main Elements: Over 98% of an organism’s mass is made up of six elements. Oxygen (O): 65% body massCellular respiration, component of water, and most organic compounds.Carbon (C): 18% of body mass. Backbone of all organic compounds.Hydrogen (H): 10% of body mass.Component of water and most organic compounds.Nitrogen (N): 3% of body mass.Component of proteins and nucleic acids (DNA/RNA)Calcium (Ca): 1.5% of body mass.Bones, teeth, clotting, muscle and nerve function.Phosphorus (P): 1% of body massBones, nucleic acids, energy transfer (ATP).Minor Elements: Found in low amounts. Between 1% and 0.01%. Potassium (K): Main positive ion inside cells.Nerve and muscle function.Sulfur (S): Component of most proteins.Sodium (Na): Main positive ion outside cells.Fluid balance, nerve function.Chlorine (Cl): Main negative ion outside cells.Fluid balance.Magnesium (Mg): Component of many enzymes and chlorophyll.Trace elements: Less than 0.01% of mass: Boron (B)Chromium (Cr)Cobalt (Co)Copper (Cu)Iron (Fe)Fluorine (F)Iodine (I)Manganese (Mn)Molybdenum (Mo)Selenium (Se)Silicon (Si)Tin (Sn)Vanadium (V)Zinc (Zn) II. Structure & Properties of Atoms Atoms: Smallest particle of an element that retains its chemical properties. Made up of three main subatomic particles. Particle Location Mass ChargeProton (p+) In nucleus 1 +1Neutron (no) In nucleus 1 0Electron (e-) Outside nucleus 0* -1* Mass is negligible for our purposes.Structure and Properties of Atoms 1. Atomic number = # protons The number of protons is unique for each elementEach element has a fixed number of protons in its nucleus. This number will never change for a given element.Written as a subscript to left of element symbol. Examples: 6C, 8O, 16S, 20CaBecause atoms are electrically neutral (no charge), the number of electrons and protons are always the same.In the periodic table elements are organized by increasing atomic number. Structure and Properties of Atoms:2. Mass number = # protons + # neutronsGives the mass of a specific atom.Written as a superscript to the left of the element symbol. Examples: 12C, 16O, 32S, 40Ca. The number of protons for an element is always the same, but the number of neutrons may vary.The number of neutrons can be determined by: # neutrons = Mass number - Atomic number Structure and Properties of Atoms:3. Isotopes: Variant forms of the same element.Isotopes have different numbers of neutrons and therefore different masses.Isotopes have the same numbers of protons and electrons.Example: In nature there are three forms or isotopes of carbon (6C):12C: About 99% of atoms. Have 6 p+, 6 no, and 6 e-.13C: About 1% of atoms. Have 6 p+, 7 no, and 6 e-. 14C: Found in tiny quantities. Have 6 p+, 8 no, and 6 e-. Radioactive form (unstable). Used for dating fossils.Electron Arrangements of Important Elements of Life1 Valence electron4 Valence electrons5 Valence electrons6 Valence electronsIII. How Atoms Form Molecules: Chemical BondsMolecule: Two or more atoms combined chemically.Compound: A substance with two or more elements combined in a fixed ratio.Water (H2O)Hydrogen peroxide (H2O2)Carbon dioxide (CO2)Carbon monoxide (CO)Table salt (NaCl)Atoms are linked by chemical bonds.Chemical Formula: Describes the chemical composition of a molecule of a compound. Symbols indicate the type of atomsSubscripts indicate the number of atomsHow Atoms Form Molecules: Chemical Bonds “Octet Rule”: When the outer shell of an atom is not full, i.e.: contains fewer than 8 (or 2) electrons (valence e-), the atom tends to gain, lose, or share electrons to achieve a complete outer shell (8, 2, or 0) electrons.Example: Sodium has 11 electrons, 1 valence electron.Sodium loses its electron, becoming an ion:Na -------> Na+ + 1 e-1(2), 2(8), 3(1) 1(2), 2(8)Outer shell has 1 e- Outer shell is fullSodium atom Sodium ionNumber of valence electrons determine the chemical behavior of atoms.Element Valence Combining Tendency Electrons CapacitySodium 1 1 Lose 1Calcium 2 2 Lose 2Aluminum 3 3 Lose 3Carbon 4 4 Share 4Nitrogen 5 3 Gain 3Oxygen 6 2 Gain 2Chlorine 7 1 Gain 1Neon* 8 0 Stable* Noble gasHow Atoms Form Molecules: Chemical BondsAtoms can lose, gain, or share electrons to satisfy octet rule (fill outermost shell).Two main types of Chemical Bonds A. Ionic bond: Atoms gain or lose electrons B. Covalent bond: Atoms share electronsA. Ionic Bond: Atoms gain or lose electrons. Bonds are attractions between ions of opposite charge. Ionic compound: One consisting of ionic bonds. Na + Cl ----------> Na+ Cl- sodium chlorine Table salt (Sodium chloride)Two Types of Ions:Anions: Negatively charged particle (Cl-)Cations: Positively charged particle (Na+)B. Covalent Bond: Involves the “sharing” of one or more pairs of electrons between atoms. Covalent compound: One consisting of covalent bonds. Example: Methane (CH4): Main component of natural gas. H | H---C---H | HEach line represents on shared pair of electrons.Octet rule is satisfied: Carbon has 8 electrons,Hydrogen has 2 electronsThere may be more than one covalent bond between atoms:1. Single bond: One electron pair is shared between two atoms. Example: Chlorine (Cl2), water (H2O); methane (CH4) Cl --- Cl2. Double bond: Two electron pairs share between atoms. Example: Oxygen gas (O2); carbon dioxide (CO2) O=O3. Triple bond: Three electron pairs shared between two atoms. Example: Nitrogen gas (N2) N = N -- Number of covalent bonds formed by important elements: Carbon (4) Nitrogen (3)Oxygen (2)Sulfur (2)Hydrogen (1)Two Types of Covalent Bonds: Polar and NonpolarElectronegativity: A measure of an atom’s ability to attract and hold onto a shared pair of electrons. Some atoms such as oxygen or nitrogen have a much higher electronegativity than others, such as carbon and hydrogen.Element Electronegativity O 3.5 N 3.0S & C 2.5P & H 2.1Polar and Nonpolar Covalent BondsA. Nonpolar Covalent Bond: When the atoms in a bond have equal or similar attraction for the electrons (electronegativity), they are shared equally. Example: O2, H2, Cl2Nonpolar Covalent Bonds: Electrons are Shared EquallyPolar and Nonpolar Covalent BondsB. Polar Covalent Bond: When the atoms in a bond have different electronegativities, the electrons are shared unequally. Electrons are closer to the more electronegative atom creating a polarity or partial charge. Example: H2O Oxygen has a partial negative charge. Hydrogens have partial positive charges.Other Bonds: Weak chemical bonds are important in the chemistry of living things.Hydrogen bonds: Attraction between the partially positive H of one molecule and a partially negative atom of anotherHydrogen bonds are about 20 X easier to break than a normal covalent bond.Responsible for many properties of water.Determine 3 dimensional shape of DNA and proteins.Chemical signaling (molecule to receptor).Water: The Ideal Compound for LifeLiving cells are 70-90% waterWater covers 3/4 of earth’s surfaceWater is the ideal solvent for chemical reactionsOn earth, water exists as gas, liquid, and solidI. Polarity of water causes hydrogen bondingWater molecules are held together by H-bondingPartially positive H attracted to partially negative O atom.Individual H bond are weak, but the cumulative effect of many H bonds is very strong.H bonds only last a fraction of a second, but at any moment most molecules are hydrogen bonded to others.Unique properties of water caused by H-bondsCohesion: Water molecules stick to each other. This causes surface tension.Film-like surface of water is difficult to break.Used by some insects that live on water surface.Water forms beads.Adhesion: Water sticks to many surfaces. Capillary Action: Water tends to rise in narrow tubes. This is caused by cohesion and adhesion (water molecules stick to walls of tubes). Examples: Upward movement of water through plant vessels and fluid in blood vessels.Unique properties of water caused by H-bondsExpands when it freezes. Ice forms stable H bonds, each molecule is bonded to four neighbors (crystalline lattice). Water does not form stable H bonds.Ice is less dense than water.Ice floats on water.Life can survive in bodies of water, even though the earth has gone through many winters and ice agesUnique properties of water caused by H-bondsStable Temperature: Water resists changes in temperature because it has a high specific heat.Specific Heat: Amount of heat energy needed to raise 1 g of substance 1 degree Celsius Specific Heat of Water: 1 calorie/gram/oCHigh heat of vaporization: Water must absorb large amounts of energy (heat) to evaporate.Heat of Vaporization of Water: 540 calorie/gram.Evaporative cooling is used by many organisms to regulate body temperature.SweatingPantingUnique properties of water caused by H-bondsUniversal Solvent: Dissolves many (but not all) substances to form solutions. Solutions are homogeneous mixtures of two or more substances (salt water, air, tap water). All solutions have at least two components:Solvent: Dissolving substance (water, alcohol, oil).Aqueous solution: If solvent is water.Solute: Substance that is dissolved (salt, sugar, CO2).Water dissolves polar and ionic solutes well.Water does not dissolve nonpolar solvents well.Solubility of a Solute Depends on its Chemical NatureSolubility: Ability of substance to dissolve in a given solvent.Two Types of Solutes:A. Hydrophilic: “Water loving” dissolve easily in water.Ionic compounds (e.g. salts)Polar compounds (molecules with polar regions)Examples: Compounds with -OH groups (alcohols).“Like dissolves in like”Solubility of a Solute Depends on its Chemical NatureTwo Types of Solutes:B. Hydrophobic: “Water fearing” do not dissolve in waterNon-polar compounds (lack polar regions)Examples: Hydrocarbons with only C-H non-polar bonds, oils, gasoline, waxes, fats, etc.ACIDS, BASES, pH AND BUFFERSA. Acid: A substance that donates protons (H+). Separate into one or more protons and an anion:HCl (into H2O ) -------> H+ + Cl-H2SO4 (into H2O ) --------> H+ + HSO4- Acids INCREASE the relative [H+] of a solution.Water can also dissociate into ions, at low levels: H2O H+ + OH- B. Base: A substance that accepts protons (H+). Many bases separate into one or more positive ions (cations) and a hydroxyl group (OH- ). Bases DECREASE the relative [H+] of a solution ( and increases the relative [OH-] ). H2O H+ + OH- Directly NH3 + H+ NH4+Indirectly NaOH ---------> Na+ + OH- ( H+ + OH- H2O )Strong acids and bases: Dissociation is almost complete (99% or more of molecules). HCl (aq) -------------> H+ + Cl- NaOH (aq) -----------> Na+ + OH-(L.T. 1% in this form) (G.T. 99% in dissociated form)A relatively small amount of a strong acid or base will drastically affect the pH of solution.Weak acids and bases: A small percentage of molecules dissociate at a give time (1% or less) H2CO3 H+ + HCO3- carbonic acid Bicarbonate ion(G.T. 99% in this form) (L.T. 1% in dissociated form)C. pH scale: [H+] and [OH-]pH scale is used to measure how basic or acidic a solution is.Range of pH scale: 0 through 14.Neutral solution: pH is 7. [H+ ] = [OH-]Acidic solution: pH is less than 7. [H+ ] > [OH-]Basic solution: pH is greater than 7. [H+ ] 2H2O2 Hydrogen Oxygen 2 WaterMolecules Molecule MoleculesOrganic Chemistry: Carbon Based CompoundsA. Inorganic Compounds: Compounds without carbon.B. Organic Compounds: Compounds synthesized by cells and containing carbon (except for CO and CO2).Diverse group: Several million organic compounds are known and more are identified every day.Common: After water, organic compounds are the most common substances in cells. Over 98% of the dry weight of living cells is made up of organic compounds.Less than 2% of the dry weight of living cells is made up of inorganic compounds.Carbon: unique element for basic building block of molecules of lifeCarbon has 4 valence electrons: Can form four covalent bondsCan form single , double, triple bonds.Can form large, complex, branching molecules and rings.Carbon atoms easily bond to C, N, O, H, P, S.Huge variety of molecules can be formed based on simple bonding rules of basic chemistry Diversity of Organic CompoundsHydrocarbons: Organic molecules that contain C and H only. Good fuels, but not biologically important.Undergo combustion (burn in presence of oxygen).In general they are chemically stable.Nonpolar: Do not dissolve in water (Hydrophobic).Examples:(1C) Methane: CH4 (Natural gas).(2C) Ethane: CH3CH3(3C) Propane: CH3CH2CH3 (Gas grills).(4C) Butane: CH3CH2CH2CH3 (Lighters).(5C) Pentane: CH3CH2CH2CH2CH3(6C) Hexane: CH3CH2CH2CH2CH2CH3(7C) Heptane: CH3CH2CH2CH2CH2CH2CH3(8C) Octane: CH3CH2CH2CH2CH2CH2CH2CH3Functional groups play pivotal role in chemical & physical properties of organic molecules Compounds that are made up solely of carbon and hydrogen are not very reactive. Functional groups:One or more H atoms of the carbon skeleton may be replaced by a functional group.Groups of atoms that have unique chemical and physical properties.Usually a part of molecule that is chemically active.Similar activity from one molecule to another.Together with size and shape, determine unique bonding and chemical activity of organic molecules.Functional Groups Determine Chemical & Physical Properties of Organic MoleculesFour Important Functional Groups:Hydroxyl (-OH) Carbonyl (=C=O)Carboxyl (-COOH)Amino (-NH2)Notice that all four functional groups are polar. I. Most Biological Macromolecules are PolymersPolymer: Large molecule consisting of many identical or similar “subunits” linked through covalent bonds.Monomer: “Subunit” or building block of a polymer.Macromolecule: Large organic polymer. Most macromolecules are constructed from about 70 simple monomers.Only about 70 monomers are used by all living things on earth to construct a huge variety of moleculesStructural variation of macromolecules is the basis for the enormous diversity of life on earth.Making and Breaking PolymersThere are two main chemical mechanisms in the production and break down of macromolecules.Condensation or Dehydration SynthesisHydrolysisIn the cell these mechanisms are regulated by enzymes. Relatively few monomers are used by cells to make a huge variety of macromoleculesMacromolecule Monomers or Subunits1. Carbohydrates 20-30 monosaccharides or simple sugars2. Proteins 20 amino acids 3. Nucleic acids (DNA/RNA) 4 nucleotides (A,G,C,T/U)4. Lipids (fats and oils) ~ 20 different fatty acids and glycerol.III. Carbohydrates: Molecules that store energy and are used as building materialsGeneral Formula: (CH2O)nSimple sugars and their polymers.Diverse group includes sugars, starches, cellulose.Biological Functions: Fuels, energy storage Structural component (cell walls)DNA/RNA componentThree types of carbohydrates:A. MonosaccharidesB. Disaccharides C. PolysaccharidesA. Monosaccharides: “Mono” single & “sacchar” sugarPreferred source of chemical energy for cells (glucose)Can be synthesized by plants from light, H2O and CO2.Store energy in chemical bonds.Carbon skeletons used to synthesize other molecules.Characteristics:1. May have 3-8 carbons. -OH on each carbon; one with C=02. Names end in -ose. Based on number of carbons:5 carbon sugar: pentose 6 carbon sugar: hexose.3. Can exist in linear or ring forms4. Isomers: Many molecules with the same molecular formula, but different atomic arrangement.Example: Glucose and fructose are both C6H12O6. Fructose is sweeter than glucose.B. Disaccharides: “Di” double & “sacchar” sugarCovalent bond formed by condensation reaction between 2 monosaccharides.Examples:1. Maltose: Glucose + Glucose. Energy storage in seeds. Used to make beer.2. Lactose: Glucose + Galactose. Found in milk.Lactose intolerance is common among adults.May cause gas, cramping, bloating, diarrhea, etc.3. Sucrose: Glucose + Fructose. Most common disaccharide (table sugar). Found in plant sap.C. Polysaccharides: “Poly” many (8 to 1000)Functions: Storage of chemical energy and structure.Storage polysaccharides: Cells can store simple sugars in polysacharides and hydrolyze them when needed.1. Starch: Glucose polymer (Helical)Form of glucose storage in plants (amylose)Stored in plant cell organelles called plastids2. Glycogen: Glucose polymer (Branched)Form of glucose storage in animals (muscle and liver cells)Structural Polysaccharides: Used as structural components of cells and tissues.1. Cellulose: Glucose polymer.The major component of plant cell walls.CANNOT be digested by animal enzymes.Only microbes have enzymes to hydrolyze.2. Chitin: Polymer of an amino sugar (with NH2 group)Forms exoskeleton of arthropods (insects)Found in cell walls of some fungi Lipids: Fats, phospholipids, and steroidsDiverse groups of compounds.Composition of Lipids: C, H, and small amounts of O. Functions of Lipids:Biological fuelsEnergy storageInsulationStructural components of cell membranesHormonesLipids: Fats, phospholipids, and steroids1. Simple Lipids: Contain C, H, and O only.A. Fats (Triglycerides). Glycerol : Three carbon molecule with three hydroxyls.Fatty Acids: Carboxyl group and long hydrocarbon chains.Characteristics of fats:Most abundant lipids in living organisms.Hydrophobic (insoluble in water) because nonpolar.Economical form of energy storage (provide 2X the energy/weight than carbohydrates).Greasy or oily appearance.Lipids: Fats, phospholipids, and steroidsTypes of FatsSaturated fats: Hydrocarbons saturated with H. Lack -C=C- double bonds.Solid at room temp (butter, animal fat, lard)Unsaturated fats: Contain -C=C- double bonds.Usually liquid at room temp (corn, peanut, olive oils) 2. Complex Lipids: In addition to C, H, and O, also contain other elements, such as phosphorus, nitrogen, and sulfur.A. Phospholipids: Are composed of:Glycerol2 fatty acidPhosphate groupAmphipathic MoleculeHydrophobic fatty acid “tails”.Hydrophilic phosphate “head”.Function: Primary component of the plasma membrane of cellsB. Steroids: Lipids with four fused carbon ringsIncludes cholesterol, bile salts, reproductive, and adrenal hormones.Cholesterol: The basic steroid found in animalsCommon component of animal cell membranes.Precursor to make sex hormones (estrogen, testosterone)Generally only soluble in other fats (not in water)Too much increases chance of atherosclerosis.C. Waxes: One fatty acid linked to an alcohol.Very hydrophobic. Found in cell walls of certain bacteria, plant and insect coats. Help prevent water loss. Proteins: Large three-dimensional macromolecules responsible for most cellular functionsPolypeptide chains: Polymers of amino acids linked by peptide bonds in a SPECIFIC linear sequenceProtein: Macromolecule composed of one or more polypeptide chains folded into SPECIFIC 3-D conformationsProteins have important and varied functions:1. Enzymes: Catalysis of cellular reactions2. Structural Proteins: Maintain cell shape3. Transport: Transport in cells/bodies (e.g. hemoglobin). Channels and carriers across cell membrane.4. Communication: Chemical messengers, hormones, and receptors.5. Defensive: Antibodies and other molecules that bind to foreign molecules and help destroy them.6. Contractile: Muscular movement.7. Storage: Store amino acids for later use (e.g. egg white).Protein function is dependent upon its 3-D shape. Polypeptide: Polymer of amino acids connected in a specific sequenceA. Amino acid: The monomer of polypeptidesCentral carbonH atomCarboxyl group Amino groupV