DNA ReplicationBy : Hazirah, Nadia, Syi, WaniDNA replication
process consists of 3 steps:1. Initiation2. lon!ation3.
"er#ination1. Initiation$eplication %e!ins at partic&lar sites
called origins of replication, 'here the t'o DNA strands are
separated, openin! &p a replication (%&%%le)$eplication
proceeds in %oth directions fro# each ori!in, &ntil the entire
#olec&le is copiedAt the end of each replication %&%%le is
a replication for*, a +,shaped re!ion 'here ne' DNA strands are
elon!atin!Helicases are enzy#es that &nt'ist the do&%le
heli- at the replication for*sSin!le,strand %indin! proteins %ind
to and sta%ilize sin!le,stranded DNA"opoiso#erase corrects
(o.er'indin!) ahead of replication for*s %y %rea*in!, s'i.elin!,
and re/oinin! DNA strands DNA poly#erases III cannot initiate
synthesis of a polyn&cleotide0 they can only add
n&cleotides to the 31 end "he initial n&cleotide strand is
a short $NA pri#er. An enzy#e called pri#ase can start an $NA chain
fro# scratch and adds $NA n&cleotides one at a ti#e &sin!
the parental DNA as a te#plate2"he pri#er is short 34516
n&cleotides lon!7, and the 31 end ser.es as the startin! point
for the ne' DNA strand2. Antiparallel Elongationi.
FormationofLeadingStrand5-3."heantiparallelstr&ct&reofthedo&%leheli-
a8ects replication.DNApolymerasesIIIaddnucleotidesonlyto the free 3
end of a growing strand0 therefore,
anewDNAstrandcanelongateonlyinthe 5 to 3
direction.Alon!onete#platestrandofDNA,theDNA
polymerasesynthesizesaleadingstrand contin&o&sly, #o.in!
to'ard the replication for*ii. Formation of lagging Strand
5-3.Toelongatetheothernewstrand,called
thelaggingstrand,DNApolymerase mustworkinthedirectionawayfromthe
replication fork.Thelaggingstrandissynthesizedasa
seriesofsegmentscalledOkazaki fragments,whicharejoined togetherby
DNA ligase3. TerminationProofreading and Repairing
DADNApoly#erasesproofreadne'ly#adeDNA, replacin! any incorrect
n&cleotidesInmismatchrepairofDNA,repairenzy#es correct errors
in %ase pairin!DNAcan%eda#a!ed%ye-pos&retohar#f&l
che#icalorphysicala!entss&chasci!arette
s#o*eand9,rays0itcanalso&nder!o spontaneo&s chan!esIn
n&cleotide excision repair, a nuclease c&ts o&t and
replaces da#a!ed stretches of DNAProof Reading ProcessMismatch
ProcessNucleotide excision repair of DNA damage!olutionary
"igni#cance of Altered DNA Nucleotidesrror rate after proofreadin!
repair is lo' %&t not zeroSe:&encechan!es#ay%eco#e
per#anentandcan%epassedonto the ne-t
!eneration"hesechan!es3#&tations7arethe
so&rceofthe!enetic.ariation&pon 'hich nat&ral selection
operates
