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Summary
This document contains notes on Chapters 7 and 8, focusing on molecular biology concepts including the Central Dogma, DNA structure, replication, transcription, translation, and bacterial genetics. It provides an overview of the flow of genetic information and molecular mechanisms within cells.
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HAPTER7&8;CoursePart2:TheBlueprintofLife& C BacterialGenetics A)Chapter7:TheBlueprintofLife,fromDNAtoprotein C entralDogmaofMolecularBiology(picturebelow) Genetics–thescienceofheredity Mole...
HAPTER7&8;CoursePart2:TheBlueprintofLife& C BacterialGenetics A)Chapter7:TheBlueprintofLife,fromDNAtoprotein C entralDogmaofMolecularBiology(picturebelow) Genetics–thescienceofheredity MolecularBiology–thesciencedealingwithDNAand proteinsynthesis ○ ThetotalDNAcontainedinthecell–genome Consistsofthechromosome(s)andany plasmids ○ Chromosomescontainthegenes Genes–sectionsofDNAthatcodefora functionalproduct ○ DNA–macromoleculemadeofnucleotides EachnucleotideinDNAhas: Nitrogenousbase(A,T,G,C) Sugar(deoxyribose) Numbered1ʹto5ʹ Aphosphate. B)Chapter7:DNAformsadoublehelix T wostrandsareheldtogetherbyhydrogenbondsbetweenbases Thebasepairingrule: ○ AalwayspairswithT(A–T) ○ GalwayspairswithC(G–C) StrandsofDNAarecomplementary ○ Sequenceofonestranddeterminesthesequenceoftheother. Nucleotidesarelinkedtogetherbycovalentphosphodiesterbonds 5ʹcarbonofonenucleotideisjoinedto3ʹcarbonofthenextnucleotide,withaphosphate betweenthem WeusuallyconsiderDNAinthe5'to3'direction ○ Startingat5'end ○ Finishingat3'end TwostrandsofDNArunantiparallel. C)Chapter7:Theflowofgeneticinformation&DNAReplication Theflowofgeneticinformation 1.DNAiscopiedbeforecelldivision-Replication ○ ○ 2.DNAisusedtomakeproteins-Geneexpression ○ 3.DNAcanflowbetweentwodifferentbacterialcells–Recombination. DNAreplication ○ OneparentaldoublestrandedDNAmoleculeisusedtomake2identicaldouble strandedDNAmolecules ○ Becausethestrandsarecomplementary: Onestrandcanserveasatemplateforsynthesisoftheotherstrand DNApolymerasereadstheorderofnucleotidesinthetemplatestrandto makeacomplementarynewstrand. 1. AsmallsegmentofthedsDNAunwindsandthestrandsareseparated ○ Formsthereplicationfork Eachseparatedstrandservesastemplateforsynthesisofacomplementarystrand ○ AShortRNAprimer*isproducedbytheenzyme:Primase ○ ServesasstartingsitefornucleotidestoformnewstrandofDNA. 2. SynthesisoftheLeadingstrand ○ DNApolymerasecanonlysynthesizeDNAinonedirection=5′→3′ i. Templatemustbereadinthe3'→5'direction ii. Followsthereplicationfork iii. Synthesisoftheleadingstrandiscontinuousinthe5'to3'direction. 3. SynthesisoftheLaggingstrand ○ DNApolymerasecanonlymakeDNAin5'to3'direction i. Butthesecondstrandmustbemadeintheoppositedirection ○ DNApolymerasesynthesizessmallfragmentsofDNA:Okazakifragments Madeinthe5'to3'direction Afterwards,theRNAprimersareremovedandthefragmentsarejoined togetherbyenzymeDNAligase. C)Chapter7:Geneexpression/Transcription&Translation Twoparts: ○ 1.Transcription–informationstoredinDNAiscopiedintoRNA SynthesisofRNAfromaDNAtemplate Sequenceiscomplementarytoagene Except:itcontainsUinsteadofT ○ ThreetypesofRNA MessengerRNA(mRNA)–carriesinformationformakingspecificprotein RibosomalRNA(rRNA)–formspartoftheribosome TransferRNA(tRNA)–transportsspecificaminoacidsforproteinsynthesis 1. Initiation a. RNApolymerasebindstothegeneatspecificsitecalledthepromoter b. Separates(melts)thetwostrands c. OnlyoneDNAstrandiscopied–thetemplate d. Thetemplateisreadinthe3'→5'directionsothatRNAcanbemadeinthe5'→3' direction. 2. Elongation a. RNApolymerasemovesalongthetemplatesynthesizingnewRNA b. AllowstheDNAtorewindbehindit 3. Translation–informationinRNAisdecodedtomakeprotein. a. WhenRNApolymeraseencounterstheterminator(endofthegene)itfallsoffthe templateandreleasesthenewlysynthesizedRNA. Thegeneticcode ○ InformationinmRNAmustbetranslatedtomakeproteins ○ Organizedintosetsof3nucleotides–codons ○ Eachcodonspecifiesanaminoacidtobeaddedduringproteinsynthesis ex.GGCspecifiestheaminoacidglycine ○ SequenceofcodonsinanmRNAdeterminessequenceofaminoacidsintheprotein ○ Threecodonsspecifynoaminoacid: –UAA,UAG,UGA –“Stopcodons” –Signaltheendofproteinsynthesis. 2.Translation ○ informationinRNAisdecodedtomakeprotein. 1. Initiation a. AribosomeassemblesonthemRNA b. atRNAcarryingtheaminoacidformyl-methionineentersthePsite c. atRNAcarryingasecondaminoacidenterstheribosome d. SpecifiedbythecodonintheAsite e. Theribosomejoinstheaminoacidstogetherbyapeptidebond. . Elongation 2 a. TheribosomemovesadistanceofonecodondownthemRNA Thenextcodonis nowinplaceintheAsite b. ThecorrecttRNAenterstheAsite,bringingwithitthenextaminoacidtobeadded c. Theaminoacidisjoinedtothechain d. Formsapolypeptide e. Elongationcontinuesuntila“stopcodon”isreached. 3. Termination a. WhenastopcodonenterstheAsite,theribosomedisassemblesandreleasesthe polypeptide b. Thepolypeptideisfoldedintothecorrectshapeandbecomesaprotein c. TheribosomecaninitiatetranslationofanothermRNA. D)Chapter8:MicrobialGenetics GeneticChangeinBacteria ○ Twomethods:Mutation*,Horizontalgenetransfer Mutation ○ AchangeinthenucleotidesequenceofDNA Maycauseachangeinaproteinencodedbyagene ○ Horizontalgenetransfer ○ Geneticinfoispassedfromonelivingcelltoanothercellofthesamegeneration ○ Ex.Plasmidtransfer Ineithercase: ○ Changeisstable,andpassedontoprogeny. E)Chapter8:Mutations Mutations ○ 1.Basesubstitution(pointmutation) Asinglenucleotideisreplacedbyanothernucleotide WhenDNAreplicates–resultsinasubstitutedbasepair ○ WhenDNAistranscribedandtranslatedcanresultinanincorrectaminoacidinthe protein Missensemutation. ○ 2.Frameshiftmutation Insertion–oneortwonucleotide(s)addedtothegene Deletion–oneortwonucleotide(s)removedfromthegene ChangesthereadingframeofthemRNA –Sequenceofaminoacidsischanged“downstream”ofmutation site –Almostalwaysresultsinanon-functionalprotein. Howdomutationsoccur? ○ Spontaneousmutation Occurinabsenceofmutagens,duetooccasionalmistakesduringDNA replication ○ Inducedmutation OccurwhenDNAdamagingagentscausechangesinDNAsequence– mutagens Ex:Radiation,somechemicals ○ Regardlessoforigin,mutationscanresultin: 1.Noeffectontheprotein(remainsfunctional)–silentmutation 2.Aproteinwithadifferentaminoacidsequencethatmayhaveanaltered function–missensemutation 3.Prematurestopcodon–Incomplete(truncated)protein,usually nonfunctional–nonsensemutation. F)Chapter8:Plasmids Plasmids ○ Selfreplicating,dsDNAmolecules ○ Containnon-essentialgenes ex.Genesfortoxinproduction ○ Fplasmids–Fertilityfactors CarrygenestomakeFpilus(orsexpilus) Involvedinconjugation(transferofgeneticmaterialbetween bacteria) ○ Rplasmids–Resistancefactors Carrygenesforantibioticresistance ○ VirPlasmids–Virulencefactors Carrygenesfortoxinproduction. Horizontalgenetransferinbacteria ○ Threebasicmethods: 1.Transformation Piecesof“naked”DNAaretakenupbyabacterialcell ie.fromdeadcells,orfromreleasedplasmids Thesepiecescanbeintegratedintothechromosome ○ Recombination ○ Canthenbepassedtoprogeny,andbecomeastablepartof thegenome. 2.Transduction SmallfragmentsofDNAtransferredbetweenbacteriaby bacteriophage ○ Virusesthatinfectbacteria Phageattachestobacterialcellwall–injectsitsDNAintothecell PhageDNAisreplicatedinsidebacterialcell PhageDNAalsoencodesenzymesthatcutthebacterium’sDNAinto fragments Asnewphagesarebeingassembled,someaccidentallyreceivea pieceofbacteriaDNAinsteadofphageDNA ○ Transducingparticle Thetransducingparticlecanthencarrybacterialgenestoanother cell Injectionmechanismisstillfullyfunctional But,bacterialDNAisinjectedintothecell IftheinjectedDNArecombineswiththeexistingchromosome,it becomesastablegeneticelement ○ ie.willbepassedtoprogeny. 3.Conjugation(bacterialmating) MediatedbygenesencodedonanFfactor Transferoccurswhena: ○ Donorcell(F+)–formsanFpilusandusesittoattachtoa recipientcell(F-) ○ Pilusretractsbringingthecellstogether ○ ThedonorcellreplicatestheFfactorasacopyispassedto therecipient ○ TherecipientbecomesanF+cell. CHAPTER13;CoursePart2:Viruses,Viroids,andPrions A)VirusesCharacteristics Viruses(fromtheLatinwordforpoison) ○ Acellularparticlescapableofinfectinghostcellsandcausingdisease ○ Notfree-living–requireahostcellinwhichtomultiply Obligateintracellularparasites Usehostmetabolicsystemsandusuallydisruptnormalhostcellfunction Featuresofviruses ○ Acellular–donothaveaplasmamembrane ○ Containasingletypeofnucleicacid–eitherDNAorRNA Surroundedbyaproteincoat Mayormaynothaveadditionalenvelopeoflipids ○ Haveveryfewoftheirownenzymes Takeoverenzymesoftheirhost. HostRange ○ VirusescaninfectAnimals,Plants,Fungi,ProtozoaandBacteria ○ Mostvirusesarespecificforasinglehostspecies* Toinfectacellthevirusmustrecognizefeaturesonthehostcellsurface ex.Somevirusesrecognizethefimbriaeofacertainbacterialspecies VIralSize ○ Electronmicroscopeisrequiredtoviewviruses ○ Rangefrom20–1000nminlength. Viralarchitecture ○ Allviruseshaveatleasttwoparts: 1.Nucleicacid CanhaveeitherDNAorRNAasthegeneticmaterial–notboth Canbesinglestrandedordoublestranded ○ Canbelinearorcircular Canbeinseveralpieces–segmented Totalamountofnucleicacid=afewthousandto250,000basepairs ○ E.colichromosome=~4,600,000basepairs. 2.Capsid Proteincoatsurroundingthenucleicacid Madeupofindividualproteinscalledcapsomeres NucleicacidandCapsid–Nucleocapsid Minimumrequiredstructureforavirus 3.Envelope Notpresentinallviruses Lipidbilayer(membrane)acquiredfromthehostcell Externalcoatingaroundthenucleocapsid Additionalviralproteinsinsertedintoenvelope–calledSpikes B)Morphology/Naming/Classification M orphology(Shape)ofViruses 1.Polyhedral ○ Usuallyicosahedral–shapewith20triangularfaces 2.Helical ○ Longrods–canberigidorflexible 3.Enveloped ○ Roughlyspherical–dictatedbylipidbilayer 4.Complex ○ Polyhedralheadwithahelicaltail ○ Onlyfoundinbacteriophages. ClassificationofViruses ○ Basedon: ○ 1.Nucleicacidtype DNAorRNA Singlestrandedor doublestranded Segmentedorsingle molecule ○ 2.Capsidstructure Polyhedral Helical ○ 3.Presenceofenvelope. C)Multiplicationofanimalviruses Multiplicationofanimalviruses ○ 1.Adsorption–attachmenttohostcell Viruseshaveattachmentsites–recognizeproteinorglycoproteinofhost membrane ○ 2.Penetration–entryintohostcell Mostenvelopedvirusesenterbyfusion–lipidsofenvelopefusewithhost cytoplasmicmembrane. Nakedvirusentersthecellviaendocytosis ○ 3.Uncoating Viralnucleicacidisfreedfromthecapsid ○ 4.Biosynthesis Viralnucleicacidsarereplicated DNAreplicationoccursinthenucleus RNAreplicationoccursinthecytoplasm Viralproteins(capsomeres)aresynthesizedinthecytoplasm Biosynthesisreliesonthehostmetabolicmachinery Ex.Replicationandtranscriptionenzymes,ribosomes. ○ 5.Maturationandassembly Newvirionsareassembled Capsomeresformthecapsid Nucleicacidenterscapsid–formsthenucleocapsid 6.Release ○ Nakedviruses–burstout,rupturehostcell–hostcelldies Envelopedviruses–budout,viruspushesthroughcytoplasmicmembrane Steadyreleaseofmatureviruses Hostcellstaysaliveforalongtime D)Interactionsbetweenvirusesandanimalhosts Interactionsbetweenvirusesandanimalhosts ○ Hostdefenseplaysmajorroleinoutcomeofviralinfection Protectsagainstotherwiselethalinfection ○ Mosthealthyhumanscarryanumberof: Viruses Antibodiestoviruses ○ Ifvirusistransferredfromtheimmunehosttoanotherindividual–canresultin infection. E)Categoriesofanimalvirusinfection Categoriesofanimalvirusinfection ○ Acuteinfections ○ Usuallyshortduration ○ Diseasesymptomsresultfromtissuedamage Lysisofhostcells–releaseandspreadofvirusparticles ○ Hostdefensesystemsgraduallyeliminatevirus Maytakedaysorweeks ○ Hostmaydeveloplonglastingimmunity ○ ex.Mumps,Influenza,Polio*. Acuteinfectionwithlatecomplications ○ Afteracuteperiod,somenon-infectiousparticlesremain Cancauseseriousdiseaseyearslater ○ ex.Measles→subacutesclerosingpanencephalitis ○ Fatalbraindisorder–occursuptotenyearsafterrecoveryfrommeasles Persistentviralinfections ○ Virusiscontinuouslypresentinbody,butmayormaynotcausedisease ie.Maybenosymptoms ○ Infectedhostcanstillserveasareservoir Cantransmitvirustoothers. Chronicviralinfection ○ Aftertheacuteperiod,infectiousvirusremainspresentatalltimes Mayormaynotcausenoticeablesymptoms ○ ex.HepatitisB(serumhepatitisvirus) Transmittedbyblood,orsexuallytransmitted Mayhaveacuteperiod–fever,nausea,jaundice Aftertheacuteperiod,virusnumbersstayhighfortherestofthepatient’s life Maycausecirrhosisorlivercanceraftermanyyears. Latentviralinfections ○ Acuteinfectionfollowedbysymptomlessperiod ○ Thevirusintegratesacopyofit’sDNAintoahostcellchromosomeandremains dormant Provirus* Diseasecanbereactivatedyearslater Symptomsmaybedifferent ○ ex.Varicella-Zostervirus(Herpesfamily) Causes–Chickenpox(Varicella)inchildren Remainslatentforyears–nodisease Canreactivatelatertocauseshingles(Herpes-Zoster). VirusesandHumanTumors ○ Tumor–abnormalgrowthoftissue ○ Benigntumor–doesnotspread Malignanttumor–metastasizeandinvadenearbytissues(ie.Cancer) ○ Cellgrowthiscontrolledbytwotypesofgenes: Genesthatstimulatecellgrowth–proto-oncogenes* Genesthatinhibitcellgrowth–tumorsuppressorgenes Mutationsinthesegenescanleadtouncontrolledcellgrowth,tumor formationandcancer ○ Cancercausingviruses(oncogenicviruses) Carryoncogenes–genesthatinterferewiththecell’scontrolmechanisms MostareDNAviruses IntegrateviralDNAintothehostchromosomeasaprovirus Oncogenescontinuetobeexpressed Virusesassociatedwithcancersinhumans ○ HepatitisBandHepatitisC Believedtocausealmostallcasesoflivercancer ○ Epstein-Barrvirus Causesinfectiousmononucleosis Maycauselymphoma(cancerofwhitebloodcells)andsomecancersofthe noseandthroat ○ HumanPapillomavirus(HPV) Sexuallytransmitted–genitalwarts Believedtocausealmostallcasesofcervicalcancer. Virus-likeinfectiousparticles ○ Viroids NakedRNA Noproteincoat* Resultsinsomediseasesinplants notyetfoundinanimals ○ Prions Infectiousproteinparticles N ogeneticmaterial(RNAorDNA) Linkedtoseveralhumanandanimaldiseases Transmissiblespongiformencephalopathies Sponge-likeholesinthebrain E)Modeofinfection Modeofinfection ○ Seemtobetransmittedthroughfood ○ ex.Sheepinfectedwithprions–Scrapie* Eatenbycows–MadCowDisease Eatenbyhumans–variantCreutzfeldt-Jakobdisease ○ Notusuallydestroyedbyhightemperatures Canbedestroyedbyheat(480C)oracombinationofautoclavingina solutionofsodiumhydroxide(strongbase) ○ Onsetofdiseaseinhumansoccursseveralyearsafterinfection Notclearwhy–orhowitaccumulatesinthebrain Alwaysfatal–notreatmentorcure. CHAPTER14;CoursePart2:TheInnateImmuneResponse A)OverviewofInnateimmunity OverviewofInnateimmunity ○ Referstodefensesthatarepresentatbirth ○ Non-specific–actagainstall(most)microbesinthesameway ○ Nomemorycomponent–cannotrecallpreviouscontactwithaninvader ○ Alwayspresent-Itisactivebeforeaninfectionoccurs Respondsrapidly Includes: ○ Firstlinedefenses Physicalandchemicalbarriersthatpreventmicrobesfromenteringthebody ○ Secondlinedefenses Componentsthatacttoeliminatemicrobesthathaveinvadedbodytissues Cellulardefenses Moleculardefenses Feverandinflammation. B)Thefirstlineofdefense Thefirstlineofdefense ○ Physicalbarriers 1.Skin O utersurfaceofskinconsistsofdeadcellsandkeratin(aprotective protein) Frequentlyshed–removesmicrobes Dry–inhibitsgrowthofmicrobes ○ Skininfectionsaremorecommononmoistareasofskin,or inmoistenvironments Outerlayerofskinisanexcellentdefense–rarelypenetratedby microbes ○ Mostinfectionsoccurundertheskin–afterskinhasbeen broken Somemicrobesareabletoeatdeadskincellsandoilssecretedby theskin ○ Resultsinbodyodour. 2.Mucousmembranes Involvedinfluidorgasexchange Offerlessprotectionthantheskin Lineour“tracts”–ex.Digestivetract Secretemucous–aglycoprotein–keepsmembranefromdrying (cracking) ○ Trapsmicrobes Mucocilliaryescalator ○ Ciliasweepmucousaway 3.Fluidflow Saliva,tears,urine*,vaginalsecretions–movemicrobesawayfrom thebody. Antimicrobialsubstances(Chemicalbarriers) ○ 1.Acidityofbodyfluidsandskin Stomachacid–pH2 ○ Destroysmanybacteriaandtoxins Skin–fattyacidsandlacticacid–pH3–5 ○ Preventsgrowthofmanymicrobes 2.Lysozyme Enzymethatdegradespeptidoglycan Foundinsweat,tears,saliva,nasalsecretions. 3.Lactoferrin Ironbindingproteinsinmilk,mucous ○ Makesironunavailabletoslowgrowthofmicrobes 4.Defensins Shortpolypeptides Pokeholesinmicrobialmembranes Producedbyepithelialcells* 5.Thenormalmicrobiota* Acquiredshortlyafterbirth Preventgrowthofpathogens ○ CompetitiveexclusionandMicrobialantagonism. C)Thesecondlineofdefense Thesecondlineofdefense ○ Thecellsoftheimmunesystem Leukocytes–whitebloodcells Alwaysfoundinnormalblood,butincreaseinresponsetoinfection Leukocytes–threebroadgroups ○ 1.Granulocytes Havelargegranulesintheircytoplasm–visiblewith lightmicroscope Threesub-groups i.Basophils–weakphagocytes ○ Secretechemoattractants ○ Releasehistamine–causes inflammation,allergies ii.Eosinophils ○ Destroylargepathogens ○ ex.Parasiticworms ○ Produceextracellulardigestive enzymestoattackaparasite iii.Neutrophils–strongphagocytes* ○ Polymorphonuclear ○ Canleavethebloodandmigrate intotissuestodestroyinvading microbes. ○ 2.Mononuclearphagocytes Alsohavegranules–buttheyarenotvisibleunder lightmicroscope i.Monocytes–initiallynon-phagocytic ○ Leaveblood,entertissuesand changeintomacrophages*–strong phagocytes ○ Oftenfoundinorgans–filterout invadingpathogensasbloodpasses through ii.Dendriticcells ○ Phagocytizeforeignmaterialand bringittotheadaptiveimmune systemfor‘inspection’ Antigenpresentation ○ 3.Lymphocytes–Threetypes: Naturalkillercells(NKcells) R esponsibleforkillinginfectedbodycells andtumorcells. Attackanybodycellthatdisplaysunusual proteinsinthecytoplasmicmembrane TandBlymphocytes–partofadaptiveimmunity. P hagocytes–whitebloodcellsthatusephagocytosisto“eat”microbes. D)Moleculardefenses&Resultofactivatingthecomplementcascade Moleculardefenses ○ 1.TheComplementSystem About30Proteinsthatcirculateinblood Worktogetherinacascade Actionofoneproteintriggersactionofthenext Complementcanbetriggeredseveralways: Smallmoleculesbindingtothesurfaceofinvadingmicrobes. Resultofactivatingthecomplementcascade ○ 1.Opsonization Attachtomicrobesandactasaflagtoattractphagocytes Increasesphagocytosisby1000x ○ 2.Enhanceinflammation Increasebloodvesselpermeability Attractphagocytestoinfectionsite. ○ 3.Lysisofforeigncells Formationofmembraneattackcomplexes(MACs) Pokesholesinmembranes KillsGramnegativebacteria,butnotGrampositivebacteria.* E)TheInflammatoryResponse TheInflammatoryResponse ○ Inresponsetotissuedamage:bloodvesselsdilate,fluidsleakandleukocytes migrateintotissues Morebloodreachesarea Allowsphagocytestoentertissues–increasedphagocytosis Bringsplatelets*toformbloodclots,andnutrientsforfasterrepair. Signsandsymptomsofinflammation: ○ Pain,swelling ○ Heat,Redness ○ Edema ○ Lossoffunction. Fever ○ Canbetriggeredbytoxins,LPSorchemicalsproducedbytheimmunesystem ○ Resultsin: Rapidmusclecontraction(shivering) Increasedtemperature ○ Benefits: Fasterphagocytosis Slowsgrowthofheatlimitedmicrobes ex.E.colipreferstogrowat37°C,growthslowsat40°C Fastermetabolism-healing Uptoacertaintemperature,feverisadefenseagainstdisease ○ Drawbacks: Uncomfortable Feverabove43°Ccancausedeath. Anti-viralInterferons(IFNs) ○ ProducedwhencellsdetectviralRNA ○ Releasedbyinfectedcellstowarnneighboringcells Inducesneighboringcellstoenterintoanantiviralstate Doesnothelpcellsthatarealreadyinfected Neighboringcellsundergoapoptosisifinfected. CHAPTER15;CoursePart2:TheAdaptiveImmuneResponse A)Adaptiveimmuneresponse Adaptiveimmuneresponse Canbeacquiredeithernaturallyorartificially Naturaladaptiveimmunity:anorganismortoxinentersthebodyandpromotesanimmune response Artificialadaptiveimmunity:resultsfromimmunizationwithavaccine Bothtypesarespecificandhavememory Specific Adaptiveimmuneresponseprotectsagainstonepathogen Doesnotprotectagainstotherpathogens Onlyexceptioniswhentwopathogensareverycloselyrelated ○ ex.SmallpoxandCowpox Memory Resultinamuchstrongerresponseuponre-exposure Long-termimmunity–possiblyforlife. Overviewofadaptiveimmunity ○ Involvestwogeneralresponsesthatrespondagainstantigens ○ M oleculesthatinteractspecificallywiththeadaptiveimmunesystemandelicitan adaptiveresponse Exogenousantigens ○ Comefromoutside Ex.Bacteria,viruses,toxins Endogenousantigens ○ Generatedinsideabodycell. B)HumoralImmunityvsCellMediatedImmunity 1.Antibodymediatedresponse(Humoralresponse) ○ Bcells Detectexogenousantigensandproliferatetoformplasmacells Producesmallprotectivemolecules–antibodies(Ab) Bindtothesurfaceofbacteria,viruses,toxins,etc. 2.Cellmediatedresponse ○ HelperTcells(TH) Directandassistadaptiveimmunityandupregulateinnateimmunity ○ CytotoxicTcells(TC) Destroyabnormalbodycells Ex.Cellsinfectedbyviruses,cancercells. C)TheNatureofAntigens(Immunoglobulins) Antigen–antibodygenerator ○ Anymoleculethatinducesantibodyproduction,orbindstoaspecificreceptorona BorTcell ○ Eachantibodyrecognizesonlyasmallpartoftheantigencalledanepitope (antigenicdeterminant) ○ Aforeignparticle(likeabacterialcell)hasseveralantigens,andavastarrayof potentialepitopes ○ Someantigensaremoreimmunogenicthanothers Ex.Proteins*oftenelicitastrongimmuneresponse. ○ Y-shapedproteinsthatbindtoantigensinaveryspecificmanner Likea“lockandkey” Onlyanantigenwiththecorrectepitopewillbebound ○ Eachantibodybindstooneandonlyoneantigen. D)Antibodystructure E achantibodyconsistsoffourpolypeptides–2lightchains,and2heavychains,andhastwo generalparts: Twoidenticalarms–Fabregion(variablefragment) Eachwithanidenticalantigenbindingsitespecificforoneepitope ○ Onestem–Fcregion(constantfragment) ○ Bindstocomplementproteins,phagocytes,etc,allowingtheantibodytotrigger othercomponentsofimmunity. E)Sixprotectivefunctionsofantibodies 1.Cross-linking(agglutination) ○ Antigensgetstucktogether ○ Reducesnumberofinfectiousunitstobedealtwith 2.Neutralization ○ Abbindstoandinactivatestoxins,bacteria,viruses ○ Blocksattachmentsites 3.Complementactivation ○ Abbindsbacteria–actsasstartingpointforcomplementpathway ○ MACattack. 4.Opsonization ○ Abflagsdownphagocyticcells–toengulfanddestroytheantigen 5.Abdependentcytotoxicity ○ Abflagsdownimmunesystemcellstodestroyabnormalorinfectedbodycells 6.Immobilizationandpreventionofadherence ○ Abbindstoflagellatostoppathogenfrommoving ○ Topilitostopbacteriafromcolonizing. F)Fiveclassesofantibodies(GAMED/MEGAD) 1.IgG–immunoglobulinG ○ Mostabundant ○ Bindstoantigenverystrongly ○ Foundintheblood–butcanalsoentertissuesinregionsofinflammation Cancrossplacenta–conferspassiveimmunitytofetus* 2.IgM–immunoglobulinM ○ Consistof5unitsofAb–apentamer ○ DoesnotmoveasfreelyasIgG–IgMstaysintheblood OftenattachedtosurfaceofBcells ○ FirstAbproduceduponinfection ○ Verygoodatcross-linkingantigens. 3.IgA–immunoglobulinA ○ Consistsof2unitsofAb–adimer ○ AlsoknownassecretoryAb Foundinbodysecretions–saliva,mucous,tears,milk ○ Functionstoprotectmucosalsurfaces Protectsgastrointestinaltractofnewborns 4.IgD ○ F unctionunknown.FoundinserumandBack-upincaseIgGnon-functionalornot made? 5.IgE ○ Foundonthesurfaceofcertainimmunesystemcells MastcellsandBasophils Whenitbindstoantigens–thecellreleaseshistamine Attractscomplementandphagocytestothearea Histamineisresponsibleforallergysymptoms. G)Cellsoftheadaptiveimmunesystem 1.Lymphocytes ○ B–lymphocytes(Bcells) Antibodyproducingcells* Involvedinhumoralimmuneresponse ○ T–lymphocytes(Tcells) HelperTcells(THcells) HelpBandTccellsprepareforanimmuneresponse CytotoxicTcells(Tccells) Destroyabnormalbodycells Ex.Cellsinfectedbyvirusesandcancercells. 2.Antigenpresentingcells(APC) ○ Macrophages,Bcells,dendriticcells 1.Foreignmaterial(ex.Bacterialcell)isengulfedbyAPC 2.AntigenisprocessedandpresentedtoTcellsalongwithselfantigens Selfantigens–partofMajorhistocompatibilitycomplex(MHC) Checktopreventdestructionofourowncellsbymistake 3.Tcellsbecomeactivatedagainsttheforeignmaterial. H)TheB-CellResponse:Humoralimmunity E achnaïveBcellcarriesIgforoneepitopeonitssurface Circulateinblood,andgatherinlymphoidorgans* Ifitencountersitsspecificepitopeitwillbecomeactivated ○ Bcellreceptorbindstotheepitopeontheantigen Clonalselection ○ Antigenisphagocytized ○ Antigenisdigestedintosmallfragments. SmallfragmentsarepresentedonsurfacealongwithMHCclassIItoT-helpercells(TH) IfaTHrecognizesthefragmentasforeign,itactivatestheBcelltomultiplyanddifferentiate ○ –Bcellundergoesclonalexpansion. I)Clonalexpansion TheactivatedBcelldividesanddifferentiatesinto: ○ 1.Plasmacells Abproducingcells Shortlifespan,producealotofAb ○ 2.MemoryBcells Longliving:20–30years Circulateinblood IfitencountersAgagainitwillquicklymultiplyandchangeintoAb producingplasmacells. J)Immunologicmemory 1.Primaryresponse ○ BcellsproducelowlevelsofAb ○ Slowprocess–takes7–14days ○ IgMfirst,followedbyIgGandIgA ○ Majoroutcome:memoryisbuiltfortheantigen 2.Secondaryresponse ○ HighlevelsofIgG ○ Fastresponsetime:takes1–2days ○ Quicklyovercomestheinfection ○ Memorycellsarereplenished. TheTcellResponse:Cell-MediatedImmunity ○ TC(CytotoxicTcells)–responsiblefordestroyingabnormalcells Ex.cellsinfectedbyvirusesorbacteria,cancercells,foreigncells RecognizeantigenspresentedalongwithMHCclassI ○ Tcellactivation Adendriticcellengulfsforeignantigen,presentsantigentoaspecificTc Tcisactivatedtoundergoclonalexpansion Produces: ○ MemoryTcells ○ CytotoxicTlymphocytes(CTLs). ○ OncetheCTLsareactivated-anybodycellcanserveasAPC ○ EndogenousantigenispresentedonthecellsurfacealongwithMHCclassI CTLattachestoabnormalcellandreleases: Perforins–enzymesthatpokeholesintheabnormalcell’s membrane Granzymes–enzymesthatinduceapoptosis(programmedcell death). CHAPTER16;CoursePart2:Host-MicrobeInteractions A)PrinciplesofDisease Term Definition Example Pathogen rganismthatcancause O Streptococcuspyogenes disease Pathogenicity Abilitytocausedisease Yes,itispathogenic Virulence S everityofdisease(abilityto ighlyvirulent(somestrains H causeharm) aremorevirulentthanothers dependingontheirvirulence factors) Infection rowthofpathogensinthe G Infectiondoesn’talwayslead body toillness/disease Disease bnormalstatewherethe A e.g.,Strepthroat(butsome bodyisnotcapableof morevirulentstrainscancause performingnormalfunctions necrotizingfasciitis) Pathology Thestudyofdisease Studyingstrepthroat Etiology Causeofthedisease S tudyingwhatcausesstrep throat Pathogenesis Howthediseasedevelops S tudyinghowstrepthroat develops B)Thehumanmicrobiota(thehumanmicrobiome)Composition Atypicalhumanbodyhasapprox.10bacterialcellsforeachhumancell ○ Newdataactuallysuggeststheratioiscloserto1:1(itisestimatedtobe3.0x1013 humancellsandharborsapprox.3.8x1013bacteria(Sendersetal.,2016)) YourMicrobiotaisMadeupof: ○ Normalmicrobiota–permanentresidents ○ Transientmicrobiota–notpermanentresidents,butmaybepresentfordays,weeks ormonths C)Thehumanmicrobiota(thehumanmicrobiome)Location M icrobiotaislocalizedtoc ertainpartsofthebody Generallyexposedareas ○ ex.Skin,respiratory,intestinalandurinarytracts Internaltissues(blood,muscle,brain,etc.)arenormallyfreeofmicrobes. D)Roleofthemicrobiota Benefitthehostbypreventinggrowthofpathogens ○ Microbialantagonism–membersofthemicrobiotaproducesubstancesharmfulto invadingmicrobes ○ Competitiveexclusion–microbiotauseupavailablenutrientspreventinggrowthof pathogens E.g.,)Clostridioidesdifficile(previouslyClostridiumdifficile)–isinhibited bythenormalmicrobiotaofthelargeintestine Ifnormalmicrobiotaiseliminated(antibiotictreatments),C.difficilecan causeinfection canleadtofatalinflammationofthecolon Otherbenefitsofthemicrobiota: Somebacteriaproduceenzymesthataiddigestion E.coliinthelargeintestinemakesvitaminsKandB E)Opportunisticpathogens Microbesthatarepartofthenormalmicrobiota ○ Donotnormallycausedisease ○ Cancausediseaseif: Transferredtoanotherpartofthebody Humanhostbecomesimmuno-compromised Normalmicrobiotaisdisturbed ex.E.coli–normalresidentofthelargeintestine ○ iftransferredtourinarytractcancauseinfection ex.Streptococcuspneumoniaeisanormalresidentoftherespiratorytract ○ Whenhostisalreadyweakened(ex.Afterhavingacold) ○ Cancausepneumonia F)Signs,Symptoms,andSyndromes Symptoms–Whatapatientfeels ○ ex.Pain,malaise ○ Subjectiveandvariable Signs–anobjectivechangeaphysiciancanmeasure ○ ex.Lesions,swelling,fever,paralysis Syndrome–aspecificgroupofsymptomsandsignsthatalwaysaccompanyaparticular disease ○ ex.Carpaltunnelsyndrome,downsyndrome G)Classificationofdisease D iseasescanbeclassifiedbasedoneffectonhostandonpopulation Communicableorcontagiousdisease-Adiseasethatspreadsfromonehosttoanother contagiousdiseases–easilyspread ○ ○ ex.Chickenpox,measles,gonorrhea Contagiousdisease–easilyspread ○ ex.Chickenpoxandmeasles Non-communicabledisease–doesnotspreadbetweenpeople ○ ex.Arthritis,diabetes,heartdisease H)Progressionofinfectiousdisease Incubationperiod ○ Timebetweeninfectionandfirstsignsorsymptoms Prodromalperiod ○ Early,mildsymptoms ○ ex.Malaise Periodofillness ○ Mostseveresignsandsymptoms ○ Activeimmuneresponse–maycausesomesignsandsymptoms ex.Fever ○ Ifdiseaseisnotovercome–resultsindeath. Periodofdecline ○ Signsandsymptomssubside ○ Canlasthoursordays ○ Patientvulnerabletosecondaryinfections Periodofconvalescence ○ Recoveryoccurs ○ Thepathogencanstillbepresentandspreadtoothers Cancarrypathogenformonthsoryears. I)Durationofsymptoms Acute–rapidlydeveloping,shortduration ○ ex.Influenza Chronic–slowtodevelop,continualduration ○ ex.Tuberculosis Latent–inactiveforperiodoftime,canbereactivated ○ ex.Coldsores–herpesvirus. J)Numberofmicrobesisimportant/Distributionofthepathogen Numberofmicrobesisimportant ○ Iftoofewmicrobesenter,immunesystemwillfightthemoffandpreventdisease ○ Likelihoodofdiseaseincreasesasmicrobenumberincreases ○ Virulenceandpathogenicityofamicrobecanbeexpressednumerically: Infectiousdose: ID50–Causesinfectionin50%ofthepopulation ex.Bacillusanthracis ○ Byingestion–ID50=250,000to1,000,000endospores ○ Byinhalation–ID50=10,000to20,000endospores ○ Throughacutintheskin–ID50=10-20endospores Potencyofatoxin expressedasLethaldose ○ LD50–Kills50%oftheinfectedpopulation. Distributionofthepathogen ○ Localizedinfection–confinedtosmallareaofthebody ○ Systemicinfection–microbesortoxinsarespreadthroughoutthebody ○ Septicemia–systemicinfectionoftheblood Bacteremia–bacteriaintheblood Toxemia–toxinsintheblood Viremia–virusesintheblood Sepsis*–lifethreateningsystemicinflammatoryresponse,usuallydueto bacteremia ○ Example:Clostridiumtetanicausesinfectionofacut Releasestoxinsintotheblood. K)Establishingthecauseofdisease Koch’sPostulates ○ Basedonthegermtheoryofdisease ○ Allowsdeterminationofspecificmicroorganismsthatcausedisease 1.Thesamepathogenshouldbepresentineverycaseofthedisease 2.Thepathogenmustbeisolatedandgrowninpureculture 3.Pathogenfromthepurecultureshouldcausediseasewheninoculated intoahealthylabanimal 4.Thesamemicrobeshouldbeisolatedagainfromtheinoculatedindividual. ExceptionstoKoch’sPostulates ○ Somebacteriawillnotgrowinpureculture ex.Treponemapallidum–causativeagentofsyphilis* ○ Somepathogenscannotbeusedtoinfectlabanimals** ex.HIV ○ Sometimesseveraldifferentmicroorganismscancausethesamedisease ex.Pneumonia ○ Sometimesonepathogencancausemanydifferentdiseases ex.Streptococcuspyogenes CausesStrepthroat,Skininfections,Scarletfever. Recall:ExamplesofPathogensandDiseases S treptococcus Streptroat roteinF P epiratory R pyogenes *Adhesins* epithelialcells S treptococcus Dentalcaries dhesinP1 A Teeth mutans *Adhesins* eisseria N Gonorrhea T ypeIVpili rethralepithelial U gonorrhoeae *Adhesins* cells E nterotoxigenicE. Traveler’sdiarrhea T ype1fimbriae Intestinal coli(ETEC) *Adhesins* epithelialcells Vibriocholerae Cholera -methlyphenylal N Intestinal aninepili epithelialcells *Adhesins* ○ P athology/Pathogenicity/Disease/Pathologen/Virulence/Infection/Siteof Colonization/VirulenceFactors ○ Colonization–theestablishmentandgrowthofamicrobeinaparticular environment. L)Mechanismsofpathogenesis E stablishingInfection 1.Adherence ○ Surfacemoleculesthatallowapathogentoattach-adhesins Oftensticktospecificreceptorsonhostcellsurface ex.Bacterialcapsules,piliandfimbriae ex.Viralspikes 2.Invasiveness ○ Abilityofapathogentoinvadeandmultiplyintissues ○ Twotypesofmoleculespromoteinvasiveness: ○ Extracellularenzymes–exoenzymes ○ Degradeoralterhostcellsandtissues Fibrinolysin–degradesfibrinclots(S.pyogenes) Collagenase–degradesconnectivetissue(VibrioandClostridium) Coagulase–promotebloodclotsaroundthebacterialcell(Staphylococci) ○ Invasin Surfaceproteinsthatcauserearrangementofhostcellcytoskeleton Forceshostcelltotakeinthebacterium Ex.Salmonellaentericaforces“ruffling”byintestinalcells M)Invasion–portalsofentry 1.Mucousmembranes ○ Respiratorytract–mostcommonportalofentry Microbesinhaledintonoseormouth–ex.Colds,influenza ○ Gastrointestinaltract Germsenterinfoodorwater Mostaredestroyedbyacid(instomach)orbybile(inintestine) Somecansurvive:ex.Vibriocholera ○ Genitourinarytract–STIs Mostpathogensrequireabrokenmucousmembrane ie.acutoramicroabrasion Conjunctiva–membranecoveringtheeye. ○ 2.Skin ○ Unbrokenskinisimpenetrablebymostmicrobes ○ Somemicrobescancauseinfectionsofhairfollicles(Cutibacteriumacnes) ○ Mostrequireawoundforentry 3.Parenteralroute ○ Microbesdepositeddirectlyintotissueswhenskinormembranesarebroken ex.Tickbitecanintroducebacteriaintohost–Lymedisease ex.Intravenousinjectionwithcontaminatedsyringe–HIV. N)Dama
