7.DNA replication and transcription and post trans modification (1).pdf

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DNA REPLICATIONMarch 16, 20211BY:MUKESH DHITAL
II. DNA REPLICATION-Definition:-The process of copying a parental DNAmolecule to form two daughter DNAmoleculesOccurs duringS phaseof cell cycleMarch 16, 20212BY:MUKESH DHITAL
III. DNA replication isSemi conservativeEach strand of parent DNAserves as a template forthe synthesis of a newstrand, producingtwonew DNA molecules, eachwith one new strand andone old strandSemiconservative DNAReplication was proved bythe experiment ofMeselson-Stahl in E.coli byusing heavy nitrogen N15March 16, 20213BY:MUKESH DHITAL
I. OVERVIEW- DNA replicationDNA replication = it isa duplication of DNAThe mechanismof DNA replication involvesStrandseparationStrand copyingThe separated strands serve astemplatefor thesynthesis of the new daughter strandsTemplate strand iscopied in the complementarysense, which is dependent onWatson- Crick basepairingPolymerization of the new strand taking place from5’ to 3’ directionbyDNA PolymeraseMarch 16, 20214BY:MUKESH DHITAL
OverviewDNA replicationMarch 16, 20215BY:MUKESH DHITAL
Some important proteins involved in eukaryoticreplication1.DNA Helicases- Strand separation2.Single stranded DNA binding proteins(SSB proteins)-Stabilization of single stranded DNA3.Topoisomerases- Removal of positivesupercoils4.Primase- Synthesis of short RNA primersthat initiatethe DNA strand synthesisMarch 16, 20216BY:MUKESH DHITAL
5.DNA Polymerases- Enzymes catalyzing template directedDNA synthesis6.Sliding DNA clamp-Processivityfactor’—Increasesprocessivityof DNA Polymerase7.RNAase HandFlap endonuclease1(FEN1)-Enzymesresponsible for excision of RNA primer8.DNA ligase- Nick sealingenzymeMarch 16, 20217BY:MUKESH DHITAL
origins of replicationSpecific start sites-‘Origin ofreplication’(oriC)It is located adjacent to anAT richsequencethat is easy to unwindInprokaryotessinglestart siteIneukaryotesmultiplestartsitesMarch 16, 20218BY:MUKESH DHITAL
March 16, 20219BY:MUKESH DHITAL
Replication bubblesBinding of initiator proteininduceslocal unwindingof DNAat an adjacent A=T rich regionThe unwound sectionappears under electronmicroscope as a bubbleand is known asReplication bubble’Multiple replicationbubblesin eukaryoticDNA- essential forrapidreplication10March 16, 2021BY:MUKESH DHITAL
Unwinding of dsDNA to provide ssDNAtemplateMany Proteins areinvolved in DNA strandseparationto generate single stranded templateDNA.They are:i. DnaA proteins- (Initial local unwinding at thereplication origin)ii. DNA Helicases- (Further unwinding ofdsDNA)iii. Single strandedDNA binding (SSB) proteinsiv. DNA TopoisomerasesMarch 16, 202111BY:MUKESH DHITAL
DNA Helicases:Hexameric proteinsinthe shape ofaringBrings aboutATP mediated unwindingof DNA helixTwo helicasesbind at the replication origin in oppositeorientationsto each of the exposed DNA single strandUsingthe energy providedfrom ATP hydrolysis, the helicasesmove in opposite directions

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DNA, MUKESH DHITAL

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