Translation in prokaryotes

This pdf encodes a variety of information regarding Molecular biology and its basic concepts like Translation and Protein synthesis. Various factorial details are provided by proper diagrams. This will help students of B.Sc. especially.

1. Translation In Prokaryotes
Assignment-2
10-Mar-20 Prepared And Presented By Apoorva B. Vaghela 1
PreparedBy ApoorvaB.Vaghela
EnrollmentNo.17BMB054
Department MicrobiologyDepartment(GIA)
Semester 6
th
Semester(ThirdYear)
Subject MolecularBiology
College ShreeM.&N.ViraniScienceCollege(Autonomous)

2. What is Translation?
•TranslationistheprocessthatConvertsanmRNAsequenceintoastringof
aminoacidsthatformaProtein.
•Itiscarriedoutinboth,EukaryoticaswellasProkaryoticOrganisms.
•ThisfundamentalprocessisresponsibleforCreatingtheProteinsthatmake
upmostcells.
•ItalsomarkstheFinalStepinthejourneyfromDNAsequencetoa
functionalprotein;thelastpieceofthe“CentralDogma”tomolecular
biology.
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3. The genetic code
•Duringtranslation,acell“reads”theinformationinamessengerRNA
(mRNA)andusesittobuildaprotein.
•AnmRNAdoesn’talwaysencode—provideinstructionsfor—awhole
protein.Instead,whatwecansayisthatitalwaysencodesapolypeptide,or
chainofaminoacids.
•InanmRNA,theinstructionsforbuildingapolypeptideareRNA
nucleotides(As,Us,Cs,andGs)readingroupsofthree.
•Thesegroupsofthreearecalledcodons.
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4. •Thereare61codonsforaminoacids,andeachofthemis"read"tospecifya
certainaminoacidoutofthe20commonlyfoundinproteins.
•Onecodon,AUG,specifiestheaminoacidmethionineandalsoactsasastart
codontosignalthestartofproteinconstruction.
•Therearethreemorecodonsthatdonotspecifyaminoacids.Thesestop
codons,UAA,UAG,andUGA,tellthecellwhenapolypeptideiscomplete.
•Alltogether,thiscollectionofcodon-aminoacidrelationshipsiscalled
thegeneticcode,becauseitletscells“decode”anmRNAintoachainof
aminoacids.
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5. How Codons Are Decided?
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•TheNucleotidesequenceisdividedin
totriplets.
•Thesetripletsarecommonly
combinesasperthistableto
understandthemechanismoffthe
translation.
•Basedonthecombinationofthese
nucleotidesequence,therespective
aminoacidsaredecided.

6. Factors Involved In Translation
•Translationinamulti-stepprocess,performingvariousactivitiesat
differentstages.
•Theprocessrequires,
1.t-RNA
2.m-RNA
3.Ribosome
4.Aminoacids
5.TranslationalFactors
6.VariousEnzymes
7.SourcesofEnergy
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7. t-RNA
•TransferRNAs,ortRNAs,aremolecular"bridges"thatconnectmRNA
codonstotheaminoacidstheyencode.
•OneendofeachtRNAhasasequenceofthreenucleotidescalled
ananticodon,whichcanbindtospecificmRNAcodons.
•TheotherendofthetRNAcarriestheaminoacidspecifiedbythecodons.
•TherearemanydifferenttypesoftRNAs.
•Eachtypereadsoneorafewcodonsandbringstherightaminoacid
matchingthosecodons.
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8. m-RNA
•m-RNAstrandissynthesizedbytheprocessoftranscription.
•Itcontainsnucleotidesarrangedinawaythatiscomplementaryto
templateDNAstrand.
•Itcontainsastartcodon,OpenreadingFramesandaStopcodon.
•Topreventitfrombeingoperatedbyvariousenzymaticactivities,the3’end
isadenylated.
•m-RNAstrandiscommonlyoperatedsimultaneouslywiththetranscription
andtranslationprocess.
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9. Ribosomes
•Ribosomesarethestructureswherepolypeptides(proteins)arebuilt.
•TheyaremadeupofproteinandRNA(ribosomalRNA,orrRNA).
•Ribosomealsoactsasanenzyme,catalyzingthechemicalreactionthatlinks
aminoacidstogethertomakeachain.
•Sometimesmanyribosomesimultaneouslyprocessonasinglem-RNA
strandtoproduceproteins,thesestructureiscalled“POLYSOMES”.
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10. Various Sites of
Ribosome
•Eachribosomehastwosubunits,a
largeoneandasmallone,which
cometogetheraroundanmRNA.
•Theribosomeprovidesasetof
handyslotswheretRNAscanfind
theirmatchingcodonsonthemRNA
templateanddelivertheiramino
acids.
•TheseslotsarecalledtheA,P,andE
sites.
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11. Structure Of
Ribosome
•Largesubunit:(PeptidylTransferase
Center)
1.Comprisesof50swiththeMolecular
Weightof1,60,000Daltons.
2.Possesses34proteins,and2different
rRNAsequences.
•Smallsubunit:(DecodingCenter)
1.Comprisesof30shavingtheMolecular
Weightof9,00,000Daltons.
2.Possesses21proteinsand1540
nucleotidelong16srRNASequence.
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12. General Mechanism of Translation
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13. Translational Factors
•Variousfactorsplaysanimportantroleinwholetranslationprocess.
•Thesefactorsaredividedintogroupsasperthestagesoftheprocess.
•Initiationfactors(IF)arefoundduringInitiationstage.
•Elongationfactors(EF)arefoundduringElongationstage.
•Releasefactors(RF)arefoundduringTerminationstage.
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14. t-RNA Charging
•Itisanimportantprocesswhichhelpsthetranslationprocesstobegin.
•Inthisprocessthefirstt-RNAmoleculehavingMethionineischargedwith
theMethylgroup.
•Asthemethylgroupisassociatedwitht-RNA,nowitisconsideredasformyl
methioninet-RNAorInitiatort-RNA.
•ThenitgoestotheP-Siteofribosomeandgetsacteduponbydeformylase
enzyme.
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15. Process Of Translation
Termination
Elongation
Initiation
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16. Initiation
•InitiationbeginswiththesmallsubunitoftheRibosome,knownas30SSubunit.
•ThisprocessrequiresaspecialtRNAknownastheinitiatortRNA,whichbase-pairswiththestartcodon
usuallyAUGorGUG.
•AUGandGUGhaveadifferentmeaningwhentheyoccurwithinanORF,wheretheyarereadbytRNAsfor
methionine(tRNAMet)andvaline(tRNAVAL),respectively
•Withtheformationof30SInitiationComplex,initiationprocessbegins.
•Firstly30SSubunitwillpairwiththem-RNA.
•Astheybinds,InitiationFactors(IF)comeacrossandthenbindswiththe30SSubunit.
•InitiationFactorsareof3typesmainly:IF1,IF2,IF3.
•IF3BindswiththeESiteofthe30SSubunitandblockit.
•IF1andIF2willcomeandbindtotheASite.
•IF2factorhasGTPaseactivity.
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17. •RibosomeitselfcontainsanRNA[16srRNA]withinit&aparticularsequenceembeddedinitis,
consideredas“ShineDalgarnoSequence”[UCCUC].
•Whenm-RNAwillhaveComplementarySequence[AGGAG]with‘ShineDalgarnoSequence’,itsignalsthat
itisthestartsitefacingtheP-site.
•ThenasonlyP-siteisavailablefree,1rstt-RNA[formylatedmethionine]willcomeandattachwithP-site
ofribosome.
•Uponbindingof1rstt-RNAcorrectlywithP-site,IF3unblockstheE-siteandreleases.
•Thisassemblyisconsideredas30sInitiationComplex.
•Nowlarge50sSubunitcomes,havingE,P,AsitesaswellasTranslationFactorsbindingsites.
•Uponbindingoflargesubunit,GTPishydrolysedandduetoitIF2&IF1willbereleased.
•Thisassemblyisconsideredas70sInitiationComplex.
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Initiation

18. 10-Mar-20 Prepared And Presented By Apoorva B. Vaghela 18
Diagrammatic representation of Initiation

19. Elongation
•Nowaftertheformationof70sInitiationComplex,theribosomewillnowslideone
codonto3’endofthem-RNA.
•Thisprocessalsorequiresseveralfactorslike;
1.EF-TU[GTPaseactivity]
2.EF-G[GTPaseActivity]
3.EF-TS
•NowtheEF-TUalongwithGTPwillattachtothenextt-RNAandbindittotheA-Site,if
thebindingiscorrectthenbyGTPaseactivity,EF-TUwillbereleasedwithGDP.
•ET-TShaveabilitytorecycletheGTPtoGDPanditwillprovideGTPtothereleasingEF-
TUandmakethemabletoagainbindwiththenewt-RNA.
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20. •Nowtheformeraminoacidresiduewillbindtonewaminoacidbyformationofpeptide
bond.
•TranspeptidationreactiontakesplaceinthelargesubunitoftheRibosomebyan
enzymecalled“PeptidylTransferase”.
•Thisenzymehelpstheaminoacidbindingbytranspeptidation.
•EF-Gwillnowbindwiththelargesubunitandasit’sGTPwillhydrolyse,thewhole
assemblywillslide1codonto3’endofthem-RNAandGDPalongwithEF-Gwillbe
releasedandunchargedt-RNAwillbereleasedfromE-Site.
•SonowthepeptidechainwillautomaticallymovetowardsP-SiteandagainA-sitewillbe
freefornewt-RNA.
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Elongation

21. 10-Mar-20 Prepared And Presented By Apoorva B. Vaghela 21
Diagrammatic representation of Elongation

22. •InElongation,whenstopcodonwillappearonm-RNA,insteadofat-RNAthere,a
newmoleculecalledRF(ReleaseFactor)willbeput.
•RF-1(t-RNAmimickingprotein)willcomeandbindwithA-Site.
•RF-1has2domainsinitsstructure,onewillpairwithstopcodonandanother
domainhavingexonucleaseactivity,willbreakthebondbetweenlastt-RNAand
polypeptidechainfromP-Site.
•Asaresult,wholeproteinstructurecomesoutfromtheribosome.
•ThenRF-2alongwithGDPcomesandwillbreakthebondbetweenRF-1andstop
codonandthisenergywillconvertGDPintoGTPandasaresultRF-1isreleased.
•NowbothEandPsiteswillbeoccupiedbyunchargedt-RNAandA-Sitewillbe
empty.
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Termination

23. •ThenRRF(RibosomeReleaseFactor)alongwithEF-GcomesonA-Siteand
EF-GwillconvertGTPintoGDP.
•Thisprocesswilldrivetheribosomedownstreamtom-RNAandasaresult
E-Site’sunchargedt-RNAwillbereleased.
•RRFprovidessomesignalsandduetoittheIF-3comesandbindswiththe
E-Site.
•IF-3preventsattachmentofbothsubunits,souponit’sbindingm-RNAand
bothsubunitswillbeseparated.
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Termination

24. 10-Mar-20 Prepared And Presented By Apoorva B. Vaghela 24
Diagrammatic representation of Termination

25. References
•https://www.sparknotes.com/biology/molecular/translation/summary/
•https://www.khanacademy.org/science/biology/gene-expression-central-
dogma/translation-polypeptides/a/translation-overview
•https://www.youtube.com/channel/UCEPMCywJ6FPZpQ_aPEZt5JA
•[WATSON]MOLECULARBIOLOGYOFTHEGENE
•BECKER[Jeff_Hardin,_Gregory_Paul_Bertoni,_Lewis_J._Klein]
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26. Thank You
What's been gratifying is to live long enough to see
molecular biology and evolutionary biology growing
toward each other and uniting in research efforts.
E. O. Wilson
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