Y khoa, y dược - Chapter 2: Chemistry comes alive (Part B)

Chapter 2 Part B: Chemistry Comes Alive: Inorganic compoundsWater, salts, and many acids and basesDo not contain carbonOrganic compoundsCarbohydrates, fats, proteins, and nucleic acidsContain carbon, usually large, and are covalently bondedClasses of Compounds60%–80% of the volume of living cellsMost important inorganic compound in living organisms because of its propertiesWaterHigh heat capacityAbsorbs and releases heat with little temperature changePrevents sudden changes in temperatureHigh heat of vaporizationEvaporation requires large amounts of heatUseful cooling mechanismProperties of WaterPolar solvent propertiesDissolves and dissociates ionic substancesForms hydration layers around large charged molecules, e.g., proteins (colloid formation)Body’s major transport mediumProperties of Water Figure 2.12Water moleculeIons in solutionSalt crystal–++ReactivityA necessary part of hydrolysis and dehydration synthesis reactionsCushioningProtects certain organs from physical trauma, e.g., cerebrospinal fluidProperties of WaterIonic compounds that dissociate in waterContain cations other than H+ and anions other than OH–Ions (electrolytes) conduct electrical currents in solutionIons play specialized roles in body functions (e.g., sodium, potassium, calcium, and iron)Salts Both are electrolytesAcids are proton (hydrogen ion) donors (release H+ in solution)HCl  H+ + Cl– Acids and BasesBases are proton acceptors (take up H+ from solution)NaOH  Na+ + OH–OH– accepts an available proton (H+)OH– + H+  H2OBicarbonate ion (HCO3–) and ammonia (NH3) are important bases in the bodyAcids and BasesAcid solutions contain [H+]As [H+] increases, acidity increases Alkaline solutions contain bases (e.g., OH–)As [H+] decreases (or as [OH–] increases), alkalinity increases Acid-Base Concentration pH = the negative logarithm of [H+] in moles per literNeutral solutions:Pure water is pH neutral (contains equal numbers of H+ and OH–)pH of pure water = pH 7: [H+] = 10 –7 MAll neutral solutions have a pH 7pH: Acid-Base ConcentrationAcidic solutions  [H+],  pH Acidic pH: 0–6.99pH scale is logarithmic: a pH 5 solution has 10 times more H+ than a pH 6 solutionAlkaline solutions  [H+],  pHAlkaline (basic) pH: 7.01–14pH: Acid-Base ConcentrationFigure 2.13Concentration(moles/liter)[OH–]10010–1410–110–1310–210–1210–310–1110–410–1010–510–910–610–810–710–710–810–610–910–510–1010–410–1110–310–1210–210–1310–1[H+]pHExamples1M Sodiumhydroxide (pH=14)Oven cleaner, lye(pH=13.5)Household ammonia(pH=10.5–11.5)NeutralHousehold bleach(pH=9.5)Egg white (pH=8)Blood (pH=7.4)Milk (pH=6.3–6.6)Black coffee (pH=5)Wine (pH=2.5–3.5)Lemon juice; gastricjuice (pH=2)1M Hydrochloricacid (pH=0)10–1410014131211109876543210pH change interferes with cell function and may damage living tissueSlight change in pH can be fatalpH is regulated by kidneys, lungs, and buffersAcid-Base HomeostasisMixture of compounds that resist pH changes Convert strong (completely dissociated) acids or bases into weak (slightly dissociated) onesCarbonic acid-bicarbonate systemBuffersContain carbon (except CO2 and CO, which are inorganic)Unique to living systemsInclude carbohydrates, lipids, proteins, and nucleic acidsOrganic CompoundsMany are polymers—chains of similar units (monomers or building blocks)Synthesized by dehydration synthesisBroken down by hydrolysis reactionsOrganic CompoundsFigure 2.14+GlucoseFructoseWater isreleasedMonomers linked by covalent bondMonomers linked by covalent bondWater isconsumedSucrose(a) Dehydration synthesisMonomers are joined by removal of OH from one monomerand removal of H from the other at the site of bond formation.+(b) HydrolysisMonomers are released by the addition of a water molecule, adding OH to one monomer and H to the other.(c) Example reactionsDehydration synthesis of sucrose and its breakdown by hydrolysisMonomer 1Monomer 2Monomer 1Monomer 2+Sugars and starchesContain C, H, and O [(CH20)n]Three classesMonosaccharidesDisaccharidesPolysaccharidesCarbohydratesFunctionsMajor source of cellular fuel (e.g., glucose)Structural molecules (e.g., ribose sugar in RNA)CarbohydratesSimple sugars containing three to seven C atoms(CH20)nMonosaccharidesFigure 2.15aExampleHexose sugars (the hexoses shown here are isomers)ExamplePentose sugarsGlucoseFructoseGalactoseDeoxyriboseRibose(a) MonosaccharidesMonomers of carbohydratesDouble sugarsToo large to pass through cell membranesDisaccharides Figure 2.15bPLAYAnimation: DisaccharidesExampleSucrose, maltose, and lactose(these disaccharides are isomers)GlucoseFructoseGlucoseGlucoseGlucoseSucroseMaltoseLactoseGalactose(b) DisaccharidesConsist of two linked monosaccharidesPolymers of simple sugars, e.g., starch and glycogenNot very solublePolysaccharidesFigure 2.15cPLAYAnimation: PolysaccharidesExampleThis polysaccharide is a simplified representation of glycogen, a polysaccharide formed from glucose units.(c) PolysaccharidesLong branching chains (polymers) of linked monosaccharidesGlycogenContain C, H, O (less than in carbohydrates), and sometimes PInsoluble in waterMain types:Neutral fats or triglyceridesPhospholipidsSteroidsEicosanoidsLipidsPLAYAnimation: FatsNeutral fats—solid fats and liquid oilsComposed of three fatty acids bonded to a glycerol moleculeMain functionsEnergy storageInsulationProtection TriglyceridesFigure 2.16aGlycerol+3 fatty acid chainsTriglyceride,or neutral fat3 watermolecules(a) Triglyceride formation Three fatty acid chains are bound to glycerol bydehydration synthesisSaturated fatty acidsSingle bonds between C atoms; maximum number of HSolid animal fats, e.g., butterUnsaturated fatty acidsOne or more double bonds between C atomsReduced number of H atoms Plant oils, e.g., olive oilSaturation of Fatty AcidsModified triglycerides: Glycerol + two fatty acids and a phosphorus (P)-containing group“Head” and “tail” regions have different properties Important in cell membrane structurePhospholipidsFigure 2.16bPhosphorus-containinggroup (polar“head”)ExamplePhosphatidylcholineGlycerolbackbone2 fatty acid chains(nonpolar “tail”)Polar“head”Nonpolar“tail”(schematicphospholipid)(b) “Typical” structure of a phospholipid molecule Two fatty acid chains and a phosphorus-containing group areattached to the glycerol backbone.Steroids—interlocking four-ring structureCholesterol, vitamin D, steroid hormones, and bile saltsSteroidsFigure 2.16cExampleCholesterol (cholesterol is thebasis for all steroids formed in the body)(c) Simplified structure of a steroidFour interlocking hydrocarbon rings form a steroid.Other fat-soluble vitaminsVitamins A, E, and KLipoproteinsTransport fats in the bloodOther Lipids in the BodyPolymers of amino acids (20 types)Joined by peptide bondsContain C, H, O, N, and sometimes S and PProteinsFigure 2.17(a) Generalized structure of all amino acids.(b) Glycine is the simplest amino acid.(c) Aspartic acid (an acidic amino acid) has an acid group (—COOH) in the R group.(d) Lysine (a basic amino acid) has an amine group (–NH2) in the R group. (e) Cysteine (a basic amino acid) has a sulfhydryl (–SH) group in the R group, which suggests that this amino acid is likely to participate in intramolecular bonding. AminegroupAcidgroupFigure 2.18Amino acidAmino acidDipeptideDehydration synthesis:The acid group of one amino acid is bonded to the amine group of the next, with loss of a water molecule.Hydrolysis: Peptide bonds linking amino acids together are broken when water is added to the bond.+PeptidebondFigure 2.19a(a) Primary structure: The sequence of amino acids forms the polypeptide chain.Amino acidAmino acidAmino acidAmino acidAmino acidPLAYAnimation: Primary StructureFigure 2.19ba-Helix: The primary chain is coiledto form a spiral structure, which isstabilized by hydrogen bonds.b-Sheet: The primary chain “zig-zags” backand forth forming a “pleated” sheet. Adjacentstrands are held together by hydrogen bonds.(b) Secondary structure:The primary chain forms spirals (a-helices) and sheets (b-sheets).PLAYAnimation: Secondary StructureFigure 2.19cTertiary structure of prealbumin(transthyretin), a protein thattransports the thyroid hormonethyroxine in serum and cerebro-spinal fluid.(c) Tertiary structure: Superimposed on secondary structure. a-Helices and/or b-sheets are folded up to form a compact globular molecule held together by intramolecular bonds.PLAYAnimation: Tertiary StructureFigure 2.19dQuaternary structure ofa functional prealbuminmolecule. Two identicalprealbumin subunitsjoin head to tail to formthe dimer.(d) Quaternary structure: Two or more polypeptide chains, each with its own tertiary structure, combine to form a functional protein.PLAYAnimation: Quaternary StructureShape change and disruption of active sites due to environmental changes (e.g., decreased pH or increased temperature)Reversible in most cases, if normal conditions are restoredIrreversible if extreme changes damage the structure beyond repair (e.g., cooking an egg)Protein DenaturationBiological catalystsAn enzyme lowers the activation energy, increases the speed of a reaction (millions of reactions per minute!)EnzymesFigure 2.20Activationenergy requiredLess activationenergy requiredWITHOUT ENZYMEWITH ENZYMEReactantsProductProductReactantsPLAYAnimation: EnzymesDNA and RNALargest molecules in the body Contain C, O, H, N, and PBuilding block = nucleotide, composed of N-containing base, a pentose sugar, and a phosphate groupNucleic AcidsAdenine-containing RNA nucleotide with two additional phosphate groupsAdenosine Triphosphate (ATP)Figure 2.23Adenosine triphosphate (ATP)Adenosine diphosphate (ADP)Adenosine monophosphate (AMP)AdenosineAdenineRibosePhosphate groupsHigh-energy phosphatebonds can be hydrolyzedto release energy.Phosphorylation: Terminal phosphates are enzymatically transferred to and energize other molecules Such “primed” molecules perform cellular work (life processes) using the phosphate bond energyFunction of ATPFigure 2.24SoluteMembraneproteinRelaxed smoothmuscle cellContracted smoothmuscle cell+++Transport work: ATP phosphorylates transportproteins, activating them to transport solutes(ions, for example) across cell membranes.Mechanical work: ATP phosphorylates contractile proteins in muscle cells so the cells can shorten.Chemical work: ATP phosphorylates key reactants, providing energy to drive energy-absorbing chemical reactions.(a)(b)(c)