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University of Ottawa
Kathleen Gilmour

UNIT2 Gene ReplicationEnzymes of DNA ReplicationHelicase unwinds the DNAPrimase synthesizes RNA primer starting point for nucleotide assembly by DNA polymerasesDNA polymerases assemble nucleotides into a chain remove primers and fill resulting gapsDNA ligase closes remaining singlechain nicksgoes 5 to 3 reads 3 to 5semiconservative DNA goes from 2 strands to 4 one is a template one is new remains togetherBASIC PROBLEMDNA polymerase cannot start synthesis de novo need nucleophile primerDNA polymerases require a primer to initiate synthesis The primer can be a suitable DNA molecule one that has a 3OH which can be extendedIn the absence of a primer one must be provided de novo RNA polymerases can synthesize a primer RNA de novo Hence RNA polymerases are used to initiate replicationThis leads to others problems that relate to how the cell deals with these short RNAsends are called pilomeres and systeme is called pilomerase or telomerase without the system you lose the end and for each generation you will dieAssembling Antiparallel StrandsLeading strandcontinuous synthesis of this strand always occurs before the synthesis of the strand coming backDaughter has one old and one new strandLagging stranddiscontinuousbecause you have to open up the helix to synthesize backostaggered synthesis open prime synthesis open up prime synthesis synthesis back only goes as far as the primeromade in short fragments with a RNA primer at one end and extended DNA and extends to the next RNA primeroprimer is removed and gap is filled in by DNA polymeraseoOkazaki fragment use different mechanisms and protein complexeshas to open up so that the complimentary strand is available for DNA synthesis 3 prime to 5 prime on top strand because the thing were relating it to is the strand that is being synthesizedTwo Antiparallel StrandsAs DNA helix unwinds one template strand runs in a direction allowing new DNA strand to be made continuously in the direction of unwindingOther template strand is copied in short lengths that run in the direction opposite to unwindingoDiscontinuous replication produces short lengths then linked into a continuous strand
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