Bài giảng Biology - Chapter 5: The Structure and Function of Macromolecules

Chapter 5The Structure and Function of MacromoleculesOverview: The Molecules of LifeAnother level in the hierarchy of biological organization is reached when small organic molecules are joined togetherMacromoleculesAre large molecules composed of smaller moleculesAre complex in their structuresFigure 5.1Concept 5.1: Most macromolecules are polymers, built from monomers Three of the classes of life’s organic molecules are polymersCarbohydratesProteinsNucleic acidsA polymerIs a long molecule consisting of many similar building blocks called monomersThe Synthesis and Breakdown of PolymersMonomers form larger molecules by condensation reactions called dehydration reactions(a) Dehydration reaction in the synthesis of a polymerHOH123HOHOH1234HH2OShort polymerUnlinked monomerLonger polymerDehydration removes a watermolecule, forming a new bondFigure 5.2APolymers can disassemble byHydrolysis (b) Hydrolysis of a polymerHO123HHOH1234H2OHHOHydrolysis adds a watermolecule, breaking a bondFigure 5.2BThe Diversity of PolymersEach class of polymerIs formed from a specific set of monomers123HOHAlthough organisms share the same limited number of monomer types, each organism is unique based on the arrangement of monomers into polymersAn immense variety of polymers can be built from a small set of monomersConcept 5.2: Carbohydrates serve as fuel and building materialCarbohydratesInclude both sugars and their polymersSugarsMonosaccharidesAre the simplest sugarsCan be used for fuelCan be converted into other organic moleculesCan be combined into polymersExamples of monosaccharidesTriose sugars(C3H6O3)Pentose sugars(C5H10O5)Hexose sugars(C6H12O6)H C OHH C OHH C OHH C OHH C OHH C OHHO C HH C OHH C OHH C OHH C OHHO C HHO C HH C OHH C OHH C OHH C OHH C OHH C OHH C OHH C OHH C OHC OC OH C OHH C OHH C OHHO C HH C OHC OHHHHHHHHHHHHHHCCCCOOOOAldosesGlyceraldehydeRiboseGlucoseGalactoseDihydroxyacetoneRibuloseKetosesFructoseFigure 5.3MonosaccharidesMay be linearCan form ringsHH C OHHO C HH C OHH C OHH COCH123456HOH4C6CH2OH 6CH2OH5CHOHCHOHH2 C1CHOHOH4C5C3 CHHOHOHH2C1 COHHCH2OHHHOHHOHOHOHH53 24(a) Linear and ring forms. Chemical equilibrium between the linear and ring structures greatly favors the formation of rings. To form the glucose ring, carbon 1 bonds to the oxygen attached to carbon 5.OH3OHOO61Figure 5.4DisaccharidesConsist of two monosaccharidesAre joined by a glycosidic linkageExamples of disaccharides Dehydration reaction in the synthesis of maltose. The bonding of two glucose units forms maltose. The glycosidic link joins the number 1 carbon of one glucose to the number 4 carbon of the second glucose. Joining the glucose monomers in a different way would result in a different disaccharide. Dehydration reaction in the synthesis of sucrose. Sucrose is a disaccharide formed from glucose and fructose.Notice that fructose,though a hexose like glucose, forms a five-sided ring.(a)(b)HHOHHOHHOHOHOHCH2OHHHOHHOHHOHOHOHCH2OHHOHHOHHOHOHOHCH2OHHH2OH2OHHOHHOHOHOHCH2OHCH2OHHOOHHCH2OHHOHHHHOOHHCH2OHHOHHOOHOHHCH2OHHOHHOHOHCH2OHHHOOCH2OHHHOHOO12141– 4glycosidiclinkage1–2glycosidiclinkageGlucoseGlucoseGlucoseFructoseMaltoseSucroseOHHHFigure 5.5PolysaccharidesPolysaccharidesAre polymers of sugarsServe many roles in organismsStorage PolysaccharidesStarchIs a polymer consisting entirely of glucose monomersIs the major storage form of glucose in plantsChloroplastStarchAmyloseAmylopectin1 m(a) Starch: a plant polysaccharideFigure 5.6GlycogenConsists of glucose monomersIs the major storage form of glucose in animalsMitochondriaGiycogen granules0.5 m(b) Glycogen: an animal polysaccharideGlycogenFigure 5.6Structural PolysaccharidesCelluloseIs a polymer of glucoseHas different glycosidic linkages than starch(c) Cellulose: 1– 4 linkage of  glucose monomersHOOCH2OHHOHHHOHOHHHHO4CCCCCCHHHHOOHHOHOHOHHOCH2OHHHHOHOHHHHO4OHCH2OHOOHOHHO41OCH2OHOOHOHOCH2OHOOHOHCH2OHOOHOHOOCH2OHOOHOHHO4O1OHOOHOHOCH2OHOOHOOHOOHOH(a)  and  glucose ring structures(b) Starch: 1– 4 linkage of  glucose monomers1 glucose glucoseCH2OHCH2OH14411Figure 5.7 A–CPlant cells0.5 mCell wallsCellulose microfibrils in a plant cell wallMicrofibrilCH2OHCH2OHOHOHOOOHOCH2OHOOOHOCH2OHOHOHOHOOCH2OHOOOHCH2OHOOOHOOCH2OHOHCH2OHOHOOHOHOHOHOOHOHCH2OHCH2OHOHOOHCH2OHOOOHCH2OHOH Glucose monomerOOOOOOParallel cellulose molecules areheld together by hydrogenbonds between hydroxylgroups attached to carbonatoms 3 and 6.About 80 cellulosemolecules associateto form a microfibril, themain architectural unitof the plant cell wall.A cellulose moleculeis an unbranched glucose polymer.OHOHOOOHCellulosemoleculesFigure 5.8Is a major component of the tough walls that enclose plant cellsCellulose is difficult to digestCows have microbes in their stomachs to facilitate this processFigure 5.9Chitin, another important structural polysaccharideIs found in the exoskeleton of arthropodsCan be used as surgical thread(a) The structure of the chitin monomer. OCH2OHOHHHOHHNHCCH3OHH(b) Chitin forms the exoskeleton of arthropods. This cicada is molting, shedding its old exoskeleton and emergingin adult form. (c) Chitin is used to make a strong and flexible surgical thread that decomposes after the wound or incision heals.OHFigure 5.10 A–CConcept 5.3: Lipids are a diverse group of hydrophobic moleculesLipidsAre the one class of large biological molecules that do not consist of polymersShare the common trait of being hydrophobicFatsFatsAre constructed from two types of smaller molecules, a single glycerol and usually three fatty acids(b) Fat molecule (triacylglycerol)HHHHHHHHHHHHHHHHOHO HCCCHHOHOHHHHHHHHHHHHHHHHHHCCCCCCCCCCCCCCCCGlycerolFatty acid(palmitic acid)HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHOOOOOCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCOO(a) Dehydration reaction in the synthesis of a fatEster linkageFigure 5.11Fatty acidsVary in the length and number and locations of double bonds they containSaturated fatty acidsHave the maximum number of hydrogen atoms possibleHave no double bonds(a) Saturated fat and fatty acidStearic acidFigure 5.12Unsaturated fatty acidsHave one or more double bonds(b) Unsaturated fat and fatty acidcis double bondcauses bendingOleic acidFigure 5.12PhospholipidsPhospholipidsHave only two fatty acidsHave a phosphate group instead of a third fatty acidPhospholipid structureConsists of a hydrophilic “head” and hydrophobic “tails”CH2OPOOOCH2CHCH2OOCOCOPhosphateGlycerol(a) Structural formula(b) Space-filling modelFatty acids(c) Phospholipid symbolHydrophobic tailsHydrophilicheadHydrophobictails –Hydrophilic headCH2Choline+Figure 5.13 N(CH3)3The structure of phospholipidsResults in a bilayer arrangement found in cell membranesHydrophilichead WATERWATERHydrophobictail Figure 5.14SteroidsSteroidsAre lipids characterized by a carbon skeleton consisting of four fused ringsOne steroid, cholesterolIs found in cell membranesIs a precursor for some hormonesHOCH3CH3H3CCH3CH3Figure 5.15Concept 5.4: Proteins have many structures, resulting in a wide range of functionsProteinsHave many roles inside the cellAn overview of protein functionsTable 5.1EnzymesAre a type of protein that acts as a catalyst, speeding up chemical reactionsSubstrate(sucrose) Enzyme (sucrase) GlucoseOHH OH2OFructose3 Substrate is convertedto products. 1 Active site is available for a molecule of substrate, thereactant on which the enzyme acts. Substrate binds toenzyme. 224 Products are released.Figure 5.16PolypeptidesPolypeptidesAre polymers of amino acidsA proteinConsists of one or more polypeptidesAmino Acid MonomersAmino acidsAre organic molecules possessing both carboxyl and amino groupsDiffer in their properties due to differing side chains, called R groups20 different amino acids make up proteinsOO–HH3N+CCOO–HCH3H3N+CHCOO–CH3CH3CH3CCOO–HH3N+CHCH3CH2CHH3N+CH3CH3CH2CHCHH3N+CCH3CH2CH2CH3N+HCOO–CH2CH3N+HCOO–CH2NHHCOO–H3N+CCH2H2CH2NCCH2HCNonpolarGlycine (Gly)Alanine (Ala)Valine (Val)Leucine (Leu)Isoleucine (Ile)Methionine (Met)Phenylalanine (Phe)COO–Tryptophan (Trp)Proline (Pro)H3CFigure 5.17SO O–O–OHCH2CCHH3N+OO–H3N+OHCH3CHCCHO–OSHCH2CHH3N+COO–H3N+CCCH2OHHHHH3N+NH2CH2OCCCOO–NH2OCCH2CH2CCH3N+OO–OPolarElectricallycharged –OOCCH2CCH3N+HOO–O–OCCH2CCH3N+HOO–CH2CH2CH2CH2NH3+CH2CCH3N+HOO–NH2CNH2+CH2CH2CH2CCH3N+HOO–CH2NH+NHCH2CCH3N+HOO–Serine (Ser)Threonine (Thr)Cysteine (Cys)Tyrosine(Tyr)Asparagine(Asn)Glutamine(Gln)AcidicBasicAspartic acid (Asp)Glutamic acid (Glu)Lysine (Lys)Arginine (Arg)Histidine (His)Amino Acid PolymersAmino acidsAre linked by peptide bondsOHDESMOSOMESDESMOSOMESDESMOSOMESOHCH2CNHCHOHOHOHPeptidebondOHOHOHHHHHHHHHHHHHNNNNNSHSide chainsSHOOOOOH2OCH2CH2CH2CH2CH2CCCCCCCCCCPeptidebondAmino end(N-terminus)Backbone(a)Figure 5.18(b) Carboxyl end(C-terminus)Determining the Amino Acid Sequence of a PolypeptideThe amino acid sequences of polypeptidesWere first determined using chemical meansCan now be determined by automated machinesProtein Conformation and FunctionA protein’s specific conformationDetermines how it functionsTwo models of protein conformation(a) A ribbon model(b) A space-filling modelGrooveGrooveFigure 5.19 Four Levels of Protein StructurePrimary structureIs the unique sequence of amino acids in a polypeptideFigure 5.20–Amino acid subunits+H3NAmino endoCarboxyl endocGlyProThrGlyThrGlyGluSeuLysCysProLeuMetValLysValLeuAspAlaValArgGlySerProAlaGlylleSerProPheHisGluHisAlaGluValValPheThrAlaAsnAspSerGlyProArgArgTyrThrlleAlaAlaLeuLeuSerProTyrSerTyrSerThrThrAlaValValThrAsnProLysGluThrLysSerTyrTrpLysAlaLeuGluLleAspOC helix pleated sheetAmino acidsubunitsNCHCOCNHCOHRCNHCOHCRNHHRCORCHNHCOHNCORCHNHHCRCOCOCNHHRCCONHHCRCONHRCHCONHHCRCONHRCHCONHHCRCONHHCRNHOOCNCRCHOCHRNHOCRCHNHOCHCRNHCCNRHOCHCRNHOCRCHHCRNHCOCNHRCHCONHCSecondary structureIs the folding or coiling of the polypeptide into a repeating configurationIncludes the  helix and the  pleated sheetHHFigure 5.20Tertiary structureIs the overall three-dimensional shape of a polypeptideResults from interactions between amino acids and R groupsCH2CHOHOCHOCH2CH2NH3+C-OCH2OCH2SSCH2CHCH3CH3H3CH3CHydrophobic interactions and van der Waalsinteractions PolypeptidebackboneHyrdogenbondIonic bondCH2Disulfide bridgeQuaternary structureIs the overall protein structure that results from the aggregation of two or more polypeptide subunitsPolypeptidechainCollagen Chains ChainsHemoglobinIronHemeThe four levels of protein structure+H3NAmino endAmino acidsubunitshelixSickle-Cell Disease: A Simple Change in Primary StructureSickle-cell diseaseResults from a single amino acid substitution in the protein hemoglobinHemoglobin structure and sickle-cell diseaseFibers of abnormalhemoglobin deform cell into sickle shape.Primary structureSecondaryand tertiarystructuresQuaternary structureFunctionRed bloodcell shapeHemoglobin AMolecules donot associatewith oneanother, eachcarries oxygen.Normal cells arefull of individualhemoglobinmolecules, eachcarrying oxygen    10 m10 m    Primary structureSecondaryand tertiarystructuresQuaternary structureFunctionRed bloodcell shapeHemoglobin SMolecules interact with one another tocrystallize into a fiber, capacity to carry oxygen is greatly reduced. subunit subunit12345673456721Normal hemoglobinSickle-cell hemoglobin. . .. . .Figure 5.21Exposed hydrophobic regionValThrHisLeuProGlulGluValHisLeuThrProValGluWhat Determines Protein Conformation?Protein conformationDepends on the physical and chemical conditions of the protein’s environmentDenaturationIs when a protein unravels and loses its native conformationDenaturationRenaturationDenatured proteinNormal proteinFigure 5.22The Protein-Folding ProblemMost proteinsProbably go through several intermediate states on their way to a stable conformation ChaperoninsAre protein molecules that assist in the proper folding of other proteinsHollowcylinderCapChaperonin(fully assembled)Steps of ChaperoninAction: An unfolded poly- peptide enters the  cylinder from one end. The cap attaches, causing the cylinder to change shape insuch a way that it creates a hydrophilic environment for the folding of the polypeptide. The cap comesoff, and the properlyfolded protein is released.CorrectlyfoldedproteinPolypeptide213Figure 5.23X-ray crystallographyIs used to determine a protein’s three-dimensional structureX-raydiffraction patternPhotographic filmDiffracted X-raysX-raysourceX-ray beamCrystalNucleic acidProtein(a) X-ray diffraction pattern(b) 3D computer modelFigure 5.24Concept 5.5: Nucleic acids store and transmit hereditary informationGenesAre the units of inheritanceProgram the amino acid sequence of polypeptidesAre made of nucleic acidsThe Roles of Nucleic AcidsThere are two types of nucleic acidsDeoxyribonucleic acid (DNA)Ribonucleic acid (RNA)DNAStores information for the synthesis of specific proteinsDirects RNA synthesisDirects protein synthesis through RNA123 Synthesis of mRNA in the nucleusMovement of mRNA into cytoplasm via nuclear poreSynthesisof proteinNUCLEUSCYTOPLASMDNAmRNARibosomeAminoacidsPolypeptidemRNAFigure 5.25The Structure of Nucleic AcidsNucleic acidsExist as polymers called polynucleotides(a) Polynucleotide, or nucleic acid3’C5’ end5’C3’C5’C3’ endOHFigure 5.26 OOOOEach polynucleotideConsists of monomers called nucleotidesNitrogenousbaseNucleosideOOOOPCH25’C3’CPhosphategroupPentosesugar(b) NucleotideFigure 5.26 ONucleotide MonomersNucleotide monomers Are made up of nucleosides and phosphate groups(c) Nucleoside componentsFigure 5.26 CHCHUracil (in RNA)URibose (in RNA)Nitrogenous bases PyrimidinesCNNCOHNH2CHCHOCNHCHHNCOCCH3NHNCCHOOCytosineCThymine (in DNA)TNHCNCCNCCHNNH2ONHCNHHCCNNHCNH2AdenineAGuanineGPurinesOHOCH2HHHOHHOHOCH2HHHOHHPentose sugarsDeoxyribose (in DNA)Ribose (in RNA)OHOHCHCHUracil (in RNA)U4’5”3’OHH2’1’5”4’3’2’1’Nucleotide PolymersNucleotide polymers Are made up of nucleotides linked by the–OH group on the 3´ carbon of one nucleotide and the phosphate on the 5´ carbon on the nextThe sequence of bases along a nucleotide polymerIs unique for each geneThe DNA Double HelixCellular DNA moleculesHave two polynucleotides that spiral around an imaginary axisForm a double helixThe DNA double helixConsists of two antiparallel nucleotide strands3’ endSugar-phosphatebackboneBase pair (joined byhydrogen bonding)Old strandsNucleotideabout to be added to a new strandA3’ end3’ end5’ endNewstrands 3’ end5’ end5’ endFigure 5.27The nitrogenous bases in DNAForm hydrogen bonds in a complementary fashion (A with T only, and C with G only)DNA and Proteins as Tape Measures of EvolutionMolecular comparisons Help biologists sort out the evolutionary connections among species The Theme of Emergent Properties in the Chemistry of Life: A ReviewHigher levels of organizationResult in the emergence of new properties OrganizationIs the key to the chemistry of life