PROTEIN SYNTHESIS: TRANSLATION AND THE GENETIC CODE · 2010. 4. 20. · PROTEIN SYNTHESIS:...

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.