protein synthesis: translation and the genetic code · 2010. 4. 20. · protein synthesis:...
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PROTEINSYNTHESIS:TRANSLATIONANDTHEGENETICCODEHLeeYuJsuicoJunsay
DepartmentofChemistry
SchoolofScienceandEngineering
AteneodeManilaUniversity1
NucleicAcidsareimportantfortheirrolesinthestorage,transferandexpressionofgeneCcinformaCon.
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HOW DO YOU TRANSFER INFORMATION TO THE NEXT GENERATION?
HOW DO YOU DECODE THE INFORMATION AND MAINTAIN THE CELL’S STRUCTURE AND FUNCTION?
TransferandinterpretaConofgeneCcinformaConisdescribedinthecentraldogmaofmolecularbiology.
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Transla<onisrequiredtoconvertthelanguageofnucleicacidstothelanguageofproteins.
TRANSLATIONPROCESS
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TranslaConoccursintheribosomes.Ribosomesarecomposedoftwo(2)majorsubunits.EachsubunitisacomplexstructureofrRNAandseveralproteins.
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TranslaConoccursintheribosomes.Ribosomesarecomposedoftwo(2)majorsubunits.EachsubunitisacomplexstructureofrRNAandseveralproteins.
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RibosomesmovealongmRNAtemplatesdecipheringthecode,bringalongadaptormoleculescarryingaminoacidscapableofspecificbindingtomRNAtodecodeinformaCon,andcancatalyzetheformaConofthepepCdebond.
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Proteinsynthesisbeginsattheaminoterminus.
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Aminoacidsarecarriedbyt‐RNA
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Aminoacyl‐tRNAsynthetasea[achestheaminoacidtothet‐RNA(veryspecific)
Mechanismandspecificity
DeacylaseacCvity"edits"andhydrolyzesmisacylatedaminoacyl‐tRNAs
DespitecommonfuncCon,thesynthetasesareadiversecollecConofenzymes
Fourdifferentquaternarystructures:α,α2,α4andα2β2
Subunitsfrom334tomorethan1000residues
AminoacidsarecarriedbytRNA.
EachuniqueaminoacidiscarriedbyaspecifictRNA
Specificityisdeterminedbya3‐nucleoCdesequenceinmRNAcalledcodonsandthecorrespondingcomplementarysequenceintRNAcalledan<codons
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ThisspecificinteracConbetweenthecodonandacorrespondingtranslaContoanaminoacidisdeterminedbythegene<ccode.
3nucleoCdes(codon)encodeanaminoacid
Thecodeisnonoverlapping
Thecodehasnopunctua6on
Thecodeisdegenerateanduniversal
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ThisspecificinteracConbetweenthecodonandacorrespondingtranslaContoanaminoacidisdeterminedbythegene<ccode.
GENOME – ENGLISH analogy Nitrogenous Bases (ATCG) Letters (a,s,f,t,r,e,…) Codons Words Gene Sentences Chromosome Chapters Genome Book
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Problem1WhatisthepepCdeencodedbythefollowingmRNA?3’‐AGAAUAUCGAAGCAGGGGUAGUGA‐5’
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Problem2ThefollowingistheparentDNAstrand.AssumingthatsplicingdoesnotoccuranymoreadertranscripCon,givethepepCdeitexpresses.
5’-CTATAGAATCCCCCAATGACCACGCAT-3’
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TranslaConisstartedbyrecogniConofstartcodonofthesmallerribosomalunit,starttRNA,iniCaConfactors(IF)andGTP.
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NOTE:Prokaryotestartisdifferentfromtheeukaryotestart.
ProkaryoteSTART fMet(formylmethionine)boundtoiniCatortRNA
RecognizesAUGandsomeCmesGUG(buttheyalsocodeforMetandValrespecCvely)
AUG(orGUG)onlypartoftheiniCaConsignal;precededbyapurine‐richsequence
ShineDalgarnosequence
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NOTE:Prokaryotestartisdifferentfromtheeukaryotestart.
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NOTE:Prokaryotestartisdifferentfromtheeukaryotestart.
EukaryoteSTART AUGnearestthe5’endisusuallythestartsignal
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WhentranslaConisiniCated,thelargeribosomalsubunitengagestocompletetheribosomalcatalyCcsites
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WhentranslaConisiniCated,thelargeribosomalsubunitengagestocompletetheribosomalcatalyCcsites
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WhentranslaConisiniCated,thelargeribosomalsubunitengagestocompletetheribosomalcatalyCcsites
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AsecondAminoacyl‐tRNAmoleculecomesintotheA‐siteandpep<dyltransferasecreatesthepepCdebond
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AsecondAminoacyl‐tRNAmoleculecomesintotheA‐siteandpep<dyltransferasecreatesthepepCdebond
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AsecondAminoacyl‐tRNAmoleculecomesintotheA‐siteandpep<dyltransferasecreatesthepepCdebond
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AsecondAminoacyl‐tRNAmoleculecomesintotheA‐siteandpep<dyltransferasecreatesthepepCdebond
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mRNAistranslatedbylotsofribosomes,oneadertheother.
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SomeanCbioCcsinhibittranslaContokilloffbacteria.
Streptomycesvenezuelaeproducespuromuycin
RECAP:1. TranslaConoccursattheribosomes(largesubunit
andsmallsubunit)2. t‐RNAscarryspecificaminoacidstoribosomes.3. SpecificinteracConsbetweenmRNAandtRNAallow
forthedecodingandtranslaConofnucleicacidtoproteins
4. RibosomescatalyzereacConofpepCdebondformaCon
POST‐TRANSLATIONALMODIFICATIONSANDPROCESSING
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AdertranslaCon,proteinsfoldduetointermolecularinteracConswithwateranditself.
Chaperonesfacilitateandguideproteinfolding
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Proteinsarealsobiologicallymodifiedbya[achingdifferentgroups
ProteolyCccleavage(Zymogens)
A[achmentofCarbohydrates
AddiConofprostheCcgroups(heme,etc.)
AminoacidmodificaCon
PROTEIN
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ProteinsarethentransportedtodifferentpartsofthecellbymeansofproteintargeKng.
Proteinthatneedtopassthrumembraneshaveanextraaminoacidsequence(cealledsignalsequence)totellthecellthattheyneedtobetransported.
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ProteinsalsoneedtobeconCnuouslydegradedforfuncConregulaConandremovalofdamagedormisfoldedproteins.Theprotein’s“kissofdeath”markerisUbiqui<n.
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ProteinsalsoneedtobeconCnuouslydegradedforfuncConregulaConandremovalofdamagedormisfoldedproteins.Theprotein’s“kissofdeath”markerisUbiqui<n.
REGULATIONOFPROTEINSYNTHESISANDGENEEXPRESSION
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Humanshaveabout20000–25000genes.SomeareneededatallCmes(cons<tu<vegenes).Someareneededonlyatspecificpointsinacell’slife(induciblegenesorrepressiblegenes)…
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AgeneclustercontaininggenescodingfordifferentproteinsofrelatedfuncConsarecalledoperons.
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TheRNAPolymerase‐DNAinteracConisCghtlyregulatedbyac<vatorsanddeac<vators.
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TheRNAPolymerase‐DNAinteracConisCghtlyregulatedbyac<vatorsanddeac<vators.
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RegulatoryproteinshavediscretebindingdomainsthatallowthemtorecognizeandbindtospecificDNA.TheyparCcipateviaH‐bondingtoDNAsequences.
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About80%ofknownregulatoryproteinscanbeclassifiedas:1.Helix‐turn‐helixmo<f
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About80%ofknownregulatoryproteinscanbeclassifiedas:1.Helix‐turn‐helixmoCf;2.Zincfingermo<f
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About80%ofknownregulatoryproteinscanbeclassifiedas:1.Helix‐turn‐helixmoCf;2.Zincfingermo<f
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About80%ofknownregulatoryproteinscanbeclassifiedas:1.Helix‐turn‐helixmoCf;2.ZincfingermoCf;3.LeucineZippermo<f
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About80%ofknownregulatoryproteinscanbeclassifiedas:1.Helix‐turn‐helixmoCf;2.ZincfingermoCf;3.LeucineZippermo<f
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GenesmayalsobesilencedadertranscripCon(Posttranscrip<onalgenesilencing,PTGS)byuseofRNA‐inducedsilencingcomplexes(RISCs)orriboswitches.
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GenesmayalsobesilencedadertranscripCon(Posttranscrip<onalgenesilencing,PTGS)byuseofRNA‐inducedsilencingcomplexes(RISCs)orriboswitches.
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GenesmayalsobesilencedadertranscripCon(Posttranscrip<onalgenesilencing,PTGS)byuseofRNA‐inducedsilencingcomplexes(RISCs)orriboswitches.
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GenesmayalsobesilencedadertranscripCon(Posttranscrip<onalgenesilencing,PTGS)byuseofRNA‐inducedsilencingcomplexes(RISCs)orriboswitches.