Lecture 4 CSB351 Virology

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Department
Cell and Systems Biology
Course
CSB351Y1
Professor
Mounir Abou Haidar
Semester
Fall

Description
Lecture4: Pg12contd September-24-09 2:10 PM NucleicAcidEnzymes { Polymerase:enzymethatsynthesizeN.A. Pyrophosphate:needtriphosphate(cytosinetriphosphateCTP,adeninetriphosphateATP,etc)-->triphosphate,brokendownby polymerase,energyfrompyrophosphateusedtomakecovalentbond,RNADNAsynthesizedbecomesachain-likemolecule (covalentbonds,verystrong) { RNApolymerase:Doesntneedprimer a. DNA-dependentRNApolymerase: (DNAviruses) TranscriptionofmRNAfromnuclearDNA Needpromoter:sequenceofDNAthatRNApolymerasebindsto-->tostarttranscription Weakstrongpromoter:howmuchitattractsRNA polymerase Stronger=transcribingmoreRNA Virusmakestheirpromotersmoreattractivethanthatofthecell,socan usecellsmachinerytotranscribetheirown genes-->thusstrongpromotersareusuallyviral b. RNA-dependentRNApolymerase:(RNAviruses) MakenewRNAfromRNAtemplate(copyase) RNAVirusescodefortheirown,fortheirownreplication ALLRNAvirusesencodeforthis { DNA-dependentDNApolymerase:needsprimer MostDNAvirusescodefortheown,makenewDNA copyfrom RNAtemplate(reversetranscriptase) Retroviruses! P13: ModifyingEnzymes Methylases { Modifyingenzymesthataddamethyl(-CH3)group-->modifythefirstnucleotideontheRNA(mRNAor(+)viralRNA)-->first nucleotidenormallyisguanosine,atposition7(m7G)-->addmethylgroup { Getspecialstructureat5 endofall mRNAofcell-->makesriborecognizethem,isacap,likesignal -->readyfortranslation! Viral(+)RNA: majorityofthese+RNAviruseshaveacap at 5 endas well,likethemRNAs (somedont--comebacklater: polio) *MOST(+)RNAviruseshave5cap on theirmRNA!! *Polio:(+)virus,hasnocap! Why?Diffstr
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