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Transcri tionAtifHassanKhirelsiedAtifHassanKhirelsied,BSc,MSc,PhD.,BSc,MSc,PhD.

DepartmentofBiochemistryDepartmentofBiochemistryFacultyofMedicineandHealthSciencesFacultyofMedicineandHealthSciences

InternationalUniversityofAfricaInternationalUniversityofAfrica

K artoum,Su an.K artoum,Su an.

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TranscriptionisthesynthesisofRNA.

DNAservesasthetemplate forRNAsynthesis.

RNAsynthesisiscatalyzedbyRNApolymerase.

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,

Genesaret etranscriptiona y unctiona units.

Genesarepositione in istinct ociin i erent

chromosomes.

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DNAservesasthetem lateforRNAs nthesis.

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TheRNAresemblesthecodin strandofDNA.

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Prokar otictranscri tionunit.

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Prokar otictranscri tionunit.

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Theconserved signalsequencesinprokaryoticr m r .

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Prokar otes roduce ol cistronic mRNA.

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Isamultimeric protein.

Thecoreenzymeconsistsof4subunits(2).

Asigmafactor()bindstotheenzymeatinitiationto

formholoenzyme.

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Transcriptionoccursinthreestages

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.

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.

RNApolymeraserecognizethebeginningofagene.

ItbindstoDNAwithhigh'affinity tothepromoter.

Thepromotercontainssignalsdeterminingthestart

point,frequency anddirection ofsynthesis.

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o RNAPbindingtopromoterismediatedbygenespecific.

sigma()factor.

o TheRNAPthenunwinds thedoublehelixtoexposethe.

o Thefirstincorporatedbaseisalwaysapurine

triphosphate.

beforethesigmasubunitdissociates.

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Successiveincorporationof

basesmatchingthetemplatestran .

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Eachribonucleotide isinsertedintothegrowingRNA

s ran o ow ng e asepa r ngru e.

SynthesisoftheRNAproceedsinthe5 3

direction.

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Elongationcontinuesuntilspecificterminationsignal

.

InE.colitranscriptionalterminationrequiresaprotein(factor).

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Therho()factorrecognizesandbindsterminationsignalinthe3'

endofRNA.

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Simultaneoustranscriptionandtranslationin

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ImportantFeaturesofTranscription

. Transcriptionresem esrep ication.

2. RNAsynthesisrequiresaccurateandefficientinitiation.

' '.

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ImportantFeaturesofTranscription

. erep cat on,transcr pt on stemp ate epen ant.

. ranscr pt oncanoccuratsevera s tes.

. ranscr pt oncon nestospec c segments(genes).

7. TherearemanymoremoleculesofRNApolymerase

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ImportantFeaturesofTranscription

. na ,e ers ran mayserveas emp a e; a is,somegenes"run"oneway,whileothersrun

. ranscr p onprocee sa ara emuc s ower anreplication.

10. Transcriptionhasmuchlowfidelitythanreplication.

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ImportantFeaturesofTranscription

. andDNAbindingproteins..

12. Transcriptionistissuespecific.

13. Transcri tioncanoccurre eatedl to roducemultiplecopiesofRNA.