Lecture biology (6e) chapter 5 campbell, reece

CHAPTER5THESTRUCTUREAND FUNCTIONOFMACROMOLECULES SectionA:Polymerprinciples Mostmacromoleculesarepolymers Animmensevarietyofpolymerscanbebuiltfromasmallsetofmonomers Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings Introduction ã Cellsjoinsmallerorganicmoleculestogetherto formlargermolecules ã Theselargermolecules,macromolecules,maybe composedofthousandsofatomsandweighover 100,000daltons ã Thefourmajorclassesofmacromoleculesare: carbohydrates,lipids,proteins,andnucleicacids Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings 1. Most macromolecules are polymers • Three of the four classes of macromolecules form  chainlike molecules called polymers • Polymers consist of many similar or identical building  blocks linked by covalent bonds • The repeated units are small molecules called  monomers • Some monomers have other functions of their own Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • The chemical mechanisms that cells use to make and  break polymers are similar for all classes of  macromolecules • Monomers are connected by covalent bonds via a  condensation reaction or dehydration reaction • One monomer provides  a hydroxyl group and  the other provides a  hydrogen and together  these form water • This process requires  energy and is aided  by enzymes.  Fig.5.2a Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings ã Thecovalentbondsconnectingmonomersina polymeraredisassembledbyhydrolysis ã Inhydrolysisasthecovalentbondisbrokenahydrogen atomandhydroxylgroupfromasplitwatermolecule attacheswherethecovalentbondusedtobe ã Hydrolysisreactions dominatethe digestiveprocess, guidedbyspecific enzymes. Fig.5.2b Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings 2.Animmensevarietyofpolymerscanbe builtfromasmallsetofmonomers ã Each cell has thousands of different macromolecules • These molecules vary among cells of the same individual;  they vary more among unrelated individuals of a species,  and even more between species • This diversity comes from various combinations of  the 40­50 common monomers and other rarer ones • These monomers can be connected in various  combinationslikethe26lettersinthealphabetcanbe usedtocreateagreatdiversityofwords ã Biologicalmoleculesareevenmorediverse Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings CHAPTER5THESTRUCTUREAND FUNCTIONOFMACROMOLECULES SectionB:Carbohydratesư FuelandBuildingMaterial Sugars,thesmallestcarbohydrates,serveasfuelandcarbonsources Polysaccharides,thepolymersofsugars,havestorageandstructuralroles Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings Introduction ã Carbohydratesincludebothsugarsandpolymers ã Thesimplestcarbohydratesaremonosaccharidesor simplesugars • Disaccharides, double sugars, consist of two  monosaccharides joined by a condensation reaction • Polysaccharides are polymers of monosaccharides Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings 1. Sugars, the smallest carbohydrates serve  as a source of fuel and carbon sources • Monosaccharides generally have molecular formulas  that are some multiple of CH2O • For example, glucose has the formula C6H12O6 • Most names for sugars end in ­ose • Monosaccharides have a carbonyl group and  multiple hydroxyl groups • If the carbonly group is at the end, the sugar is an aldose,  ifnot,thesugarsisaketose ã Glucose,analdose,andfructose,aketose,arestructural isomers Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings ã Monosaccharidesarealsoclassifiedbythenumberofcarbonsin thebackbone ã Glucoseandothersixcarbonsugarsarehexoses • Five carbon backbones are pentoses and three carbon sugars are trioses • Monosaccharides may also exist as enantiomers.  • For example, glucose and galactose, both six­carbon aldoses,  differ in the spatial arrangement around asymmetrical carbons Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • While DNA has the information for all the cell’s  activities, it is not directly involved in the day to day  operations of the cell • Proteins are responsible for implementing the instructions  contained in DNA • Each gene along a DNA molecule directs the  synthesis of a specific type of messenger RNA  molecule (mRNA) • ThemRNAinteractswiththeproteinưsynthesizing machinerytodirecttheorderingofaminoacidsina polypeptide Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings ã TheflowofgeneticinformationisfromDNAư> RNAư>protein ã Proteinsynthesisoccurs incellularstructures calledribosomes ã Ineukaryotes,DNAis locatedinthenucleus, butmostribosomesare inthecytoplasmwith mRNAasan intermediary Fig.5.28 Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings 2.Anucleicacidstrandisapolymerof nucleotides ã Nucleicacidsarepolymersofmonomerscalled nucleotides ã Eachnucleotideconsistsofthreeparts:anitrogen base,apentosesugar,andaphosphategroup Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings Fig.5.29 Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings ã Thenitrogenbases,ringsofcarbonandnitrogen, comeintwotypes:purinesandpyrimidines ã Pyrimidineshaveasinglesixưmemberedring ã Thethreedifferentpyrimidines,cytosine(C),thymine (T),anduracil(U)differinatomsattachedtothering ã Purinehaveasixưmemberedringjoinedtoafiveư memberedring ã Thetwopurinesareadenine(A)andguanine(G) Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings ã Thepentosejoinedtothenitrogenbaseisribosein nucleotidesofRNAanddeoxyriboseinDNA ã Theonlydifferencebetweenthesugarsisthelackofan oxygenatomoncarbontwoindeoxyribose ã Thecombinationofapentoseandnucleicacidisa nucleoside ã Theadditionofaphosphategroupcreatesa nucleosidemonophosphateornucleotide Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings ã Polynucleotidesaresynthesizedbyconnectingthe sugarsofonenucleotidetothephosphateofthe nextwithaphosphodiesterlink ã Thiscreatesarepeatingbackboneofsugarư phosphateunitswiththenitrogenbasesas appendages Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings ã ThesequenceofnitrogenbasesalongaDNAor mRNApolymerisuniqueforeachgene • Genes are normally hundreds to thousands of  nucleotides long • The number of possible combinations of the four  DNA bases is limitless • The linear order of bases in a gene specifies the  order of amino acids ­ the primary structure of a  protein • The primary structure in turn determines three­ dimensional conformation and function Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings 3. Inheritance is based on replication of the  DNA double helix • An RNA molecule is a single polynucleotide chain • DNA molecules have two polynucleotide strands  thatspiralaroundanimaginaryaxistoforma doublehelix ã Thedoublehelixwasfirstproposedasthestructureof DNAin1953byJamesWatsonandFrancisCrick Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings ã Thesugarưphosphatebackbonesofthetwo polynucleotidesareontheoutsideofthehelix ã Pairs of nitrogenous  bases, one from each  strand, connect the  polynucleotide chains  with hydrogen bonds • Most DNA molecules  have thousands to  millions of base pairs.  Fig. 5.30 Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings ã Becauseoftheirshapes,onlysomebasesare compatiblewitheachother ã Adenine(A)alwayspairswiththymine(T)andguanine (G)withcytosine(C) ã Withthesebaseưpairingrules,ifweknowthe sequenceofbasesononestrand,weknowthe sequenceontheoppositestrand ã Thetwostrandsarecomplementary. Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings ã Duringpreparationsforcelldivisioneachofthe strandsservesasatemplatetoordernucleotides intoanewcomplementarystrand ã Thisresultsintwoidenticalcopiesoftheoriginal doubleưstrandedDNAmolecule ã Thecopiesarethendistributedtothedaughtercells ã Thismechanismensuresthatthegenetic informationistransmittedwheneveracell reproduces. Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings 4.WecanuseDNAandproteinsastape measuresofevolution • Genes (DNA) and their products (proteins)  document the hereditary background of an  organism • Because DNA molecules are passed from parents to  offspring, siblings have greater similarity than do  unrelated individuals of the same species • This argument can be extended to develop a  moleculargenealogybetweenspecies Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings ã Twospeciesthatappeartobecloselyưrelatedbased onfossilandmolecularevidenceshouldalsobe moresimilarinDNAandproteinsequencesthanare moredistantlyrelatedspecies ã Infact,thesequenceofaminoacidsinhemoglobin moleculesdifferbyonlyoneaminoacidbetweenhumans andgorilla ã Moredistantlyrelatedspecieshavemoredifferences. Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings ... fructoseandisthemajortransportformofsugarsinplants. Fig .5. 5a Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings ã Whileoftendrawnasalinearskeleton,inaqueous solutionsmonosaccharidesformrings. Fig .5. 5 Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings... OnegroupofaminoacidshashydrophobicR groups. Fig .5. 15a Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings ã AnothergroupofaminoacidshaspolarRgroups, makingthemhydrophilic. Fig .5. 15b Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings... Chitinalsoforms thestructural supportforthe cellwallsof manyfungi Fig .5. 9 Copyrightâ2002PearsonEducation,Inc.,publishingasBenjaminCummings CHAPTER? ?5? ?THE STRUCTURE AND  FUNCTION OF MACROMOLECULES Section C: Lipids ­ Diverse Hydrophobic Molecules