polycistronicandmonocistronic-200503163402 (1).pdf

Polycistronic and monocistronic m RNa .poly cistronic present in prokaryotic organisms.

1. Polycistronic &
Monocistronic
RNA
INDRANI KAR
M.Sc Microbiology
St. George College of Management & Science
Bengaluru North University

2. INTRODUCTION
•RNAusuallyexistsassinglestrandedpolypeptid,anduracilispresent
inseadofthymineinRNAsinglestrand.
•Inbacteriathereare3typeofRNApresentasribosomalRNA,transfer
RNAandmassesRNA.
•RibosomalRNAaremadeofbyribosomalsubunits,massengerRNAalmost
aremanytypes,transferRNAisof50differenttypes.
•Allofthesethreemoleculesresemblesthesinglestrandedstructureofthe
DNA,intramolecularandhavesomedoublestrandsregions.

4. Continue.....
•TypicallyonehalfandtwothirdofbasesinRNAarepaired,thepairing
regionsareshortcontainingsixorfewerbases.
•RNAisalsohydrolyzedtofreenucleotideseitherchemicallyorenzymatically,
atpH1thephosphodiestersbondandtheN-glycosidicbondbetweenthe
sugarsandbasesarebroken,releasingthefreebases.
•Somenucleasecleaveonlyattheendofanucleicacid,eitherthe3'orthe5'
terminus,removingthesinglenucleotideorshortoligonucleotides.

6. Transfer RNA ( t-RNA )
•TransferRNAbindstotheaminoacidstotheribosomeandstart
translation,itcarriestheaminoacidsandbindstothemessengerRNA.
•Inprimarystructureitcontactabout73to93nucleotides,three
anticodonandall4basesaremethylated.
•Inthesecondarystructureitislooklikecloverleafstructure,formsbase
pairsloops,anticodonandfragmentsstrands.
•InthetertiarystructureitisformedasLshapestructure,three
dimensionalstructureformDloop.

8. Ribosomal RNA (r-RNA)
•RibosomalRNAisafibricatepartofthepolypeptideandprovides
mechanismsfordecodingm-RNAandinteractswithtRNAduringtranslation.
•RibosomalRNAisastructurecomponentoftheribosomeandactuallyfound
inthecatalyticelementforproteinssynthesis.
•It'smostabundanttypeofRNAinthecell,itcompromisesthelargeandsmall
subunit.
•ProkaryoticRNAis70svedbergunit,aunitofthemeasurementforthe
sedimentationcoefficientorhowfastmolecularsedimentwhencentrifuged.

9. Ribosomal RNA

10. Messenger RNA (m-RNA )
•MessengerRNAistheblueprintofproteinreproduction,transcribedfromthe
DNA,transfertheinformationfromcelltonucleus.
•Transferoftheinformationisdoneintoproteinnucleotides,thatcanincodonas
geneticinformation.
•Geneticcodonaretriplebasesnucleotides,eachcodonscorrespondingtothe
specificaminoacids,sequenceofcodonendswiththeacodonthatisstopsingle.
•TheproteinsynthesisprocessrequirestransferRNA(t-RNA)fortransferredthe
information.
•Them-RNAmakesuptoonlyonlyabout5%ofthedifferenttypesofRNAfoundin
bothprokaryoticandeukaryotic.

12. Type of messengerRNA
1.PolycistronicmessengerRNA
2.MonocistronicmessengerRNA

13. Polycistronic messenger RNA
•ThemessengerRNAistranslatedintoaminoacidsbyproteinsynthesizing
machineryofthecell.
•IntheprokaryotesthemessengerRNAmoleculesoftencontaininformation
fortheaminoacidssequenceofeachdifferentpolypeptideschain,inthese
casesuchmoleculesarecalledpolycistronicmessengerRNA.
•InpolycistronicmessengerRNAthecistronisusedasthesynonymousofthe
gene----abasesequenceencodingasinglepolypeptidechain.
•ThegenethatcontainpolycistronicmessengerRNAmoleculesareoften
encodedifferenttypesofproteinsofametabolicpathway.ForexampleS.
typhimurium.

15. Continue.....
•InthecellofS.typhimurium10enzymesneededtosynthesizehistidineare
encodedonlyonemessengerRNAmolecule.
•TheuseofpolycistronicmessengerRNAisaneconomicalwayforacellto
regulatesynthesisofrelatedproteinsinacoordinatedway.
•TheprokaryotesaretheexamplesofthesynthesisofthemessengerRNA
molecule,thesynthesisoftheseveralrelatedmolecules.
•WiththepolycistronicmessengerRNAthesynthesisisregulatedbythesingle
signalmadeatthesametimeiscalledcoordinateregulation.

16. Coordinate regulations

20. THANK YOU