Translation:ProteinSynthesis•Proteinsynthesismachinery:–mRNA–tRNA–Aminoacyl-tRNAsynthetases–Ribosome•Geneticcode:–Crackingthegeneticcode–Codonusage•Translationreaction:–Initiation–Elongation–Termination–Differencebetweeneukaryotesandprokaryotesintranslation–Proteinsorting–InhibitionofproteinsynthesisbyantibioticsOutlinePeptidebondformationTranslation:biosynthesisofproteins•Translationisamongthemostconservedmechanismsacrossallorganisms•Itisthemostenergeticallycostlyforthecell.Proteinsynthesisconsumesabout80%energyofthecell•50,000ribosomesperE.colicell•Ribosomesarethemostcomplexpolymerases.MolecularweightofaribosomeinE.coliis2.7millionDaltons•TwothirdsoftheribosomeisRNA;RibosomescanbeenseeunderEM•Translationrequires:–aminoacids,–mRNAs,–tRNAs,–aminoacyltRNAsynthetases,–ribosomesProteinsynthesismachineryThethreerolesofRNAinproteinsynthesis.MessengerRNA(mRNA)istranslatedintoproteinbythejointactionoftransferRNA(tRNA)andtheribosome,whichiscomposedofnumerousproteinsandtwomajorribosomalRNA(rRNA)molecules.ThreerolesofRNAintranslation1.MessengerRNA(mRNA)carriesthegeneticinformationcopiedfromDNAintheformofaseriesofthree-basecode"words,"eachofwhichspecifiesaparticularaminoacid.2.TransferRNA(tRNA)isthekeytodecipheringthecodewordsinmRNA.EachtypeofaminoacidhasitsowntypeoftRNA,whichbindsitandcarriesittothegrowingendofapolypeptidechainifthenextcodewordonmRNAcallsforit.ThecorrecttRNAwithitsattachedaminoacidisselectedateachstepbecauseeachspecifictRNAmoleculecontainsathree-basesequencethatcanbase-pairwithitscomplementarycodewordinthemRNA.3.RibosomalRNA(rRNA)associateswithasetofproteinstoformribosomes.Thesecomplexstructures,whichphysicallymovealonganmRNAmolecule,catalyzetheassemblyofaminoacidsintoproteinchains.TheyalsobindtRNAsandvariousaccessorymoleculesnecessaryforproteinsynthesis.Ribosomesarecomposedofalargeandsmallsubunit,eachofwhichcontainsitsownrRNAmoleculeormolecules.mRNA•ORF(openreadingframe):Theproteincodingregion(s)ofeachmRNAiscomposedofacontinousn...
