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Lec 18-25 Notes.docx

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Western University
Biology 1002B
Tom Haffie

Lecture 18DNA ReplicationWhere do mutations come from anywaysDNA information is relatively stable and readily replicatedWe looked at the role of epigenetics in cancer but mutation plays a role in cancer as wellMany mutation mechanisms are involved with DNA ReplicationAntiparallel Complementary Base PairingAllows for accurate replication AT CG3 terminal OH group5 terminal Phosphate GroupReplication is SemiDiscontinuousSemiConservativeContinuous on one strandSemiContinuous on the other strandThere is always a new strand and an old strand after replication is completeReplication bubble arises from two forksProkaryotes mitochondriachloroplastOne circular genome creates one replication bubble and continues in both directions until complete Eukaryotes have several originsMore DNA to replicate therefore they have more replication bubblesThese many replication bubbles connect togetherReplication ForkTextbook gives the idea that the replicated strands are replicated in different places but they are actually made by the same replication enzymeIt appears like this because textbooks squash DNA flatElongation by DNA PolymeraseYou must present a properly paired baseIncoming nucleotides are added to the 3 OH of a properly paired previous baseBecause of this rule its the ONLY way to extendClicker x3Polymerase can only do ONE thing extend the 3 end of DNA Replication ForksHelicases unwind the DNAPrimases synthesize short RNA primersThese primers are then extended used as starting points by DNA Polymerase As the replication fork continues the primer on the lagging strand is found stranded and a new RNA primer is addedThese primers what happens to themThey stranded RNA primers are removed and replaced with DNA by anotherThis is possible because there is a 3OH available on a properly paired base The RNA primer on the leading strand only one will be degradedBut there is no 3 OH for the polymerase to use in order to replace that RNAAs a result your chromosomes will shorten after every replicationReplication AnimationA Replisome replicates both strands of DNA at the same timeContinuous strand comes in and leaves oppositeThe discontinuous strand is more complicated and does loopingThe Leading PrimerThe stranded primer will be removed and then replaced this is because there is a 3 end with a free OHThe leading primer can also be removed but it will not be replaced as it is a 5 endEvery time your DNA is replicated your chromosomes DNA shortenAfter Primer Removal telomeraseThere is a gap made or overhand after the RNA primer is removedEverything in your mind wants to extend the 5 end but it cannot be done No polymerase exists that can extend the 5 endThe only work that can be done is extending the 3 endTelomerase is a kind of DNA PolymeraseDNA Polymerase needs a template but telomerase has a built in template in order to extend the 3 endThese repeats added to the end of you chromosome are called telomeres
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