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Lecture 29

BIOL 1020 Lecture 29: Lecture 29

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Biological Sciences
BIOL 1020
Joy Stacey

Lecture 29 Antiparallel elongation The antiparallel structure of the double helix (two strands oriented in opposite directions) affects replication DNA polymerases add nucleotides only to the free 3 end of a growing strand; therefore, a new DNA strand can elongate only in the 5 to 3 direction. Along one template strand of DNA, the DNA polymerase synthesizes a leading strand (it will fashion in an open and continuous manner) continuously moving toward the replication fork. To elongate the other new strand, called the lagging strand, DNA polymerase must work in the direction away from the replication fork building to the 5 end The lagging strand is synthesized as a series of segments called Okazaki fragments, which are joined together by DNA ligase (enzyme that fixes DNA like a DNA bandaid) Primase attaches to exposed DNA strand and adds 34 bases exposing a 3 end Bases it adds are not DNA they are RNA DNA polymerase has 3 prime end that it can grow on goes from 3 to 5 Eventually it gets to a place where another small piece of RNA was added little bit of DNA between RNA sections is called an Okazaki fragment DNA ligase fixes the fragments together Leading strand goes smoothly from 3 to 5 Lagging strand goes 3 to 5 with help of primase and DNA ligase and formation of Okazaki fragments DNA replication complex The proteins that participate in DNA replication form a large complex, a DNA replication machine The DNA replication machine is probably stationary during the replication process (easier to move the DNA than the move the complex) How organisms have existed for 3.5 billion years Has been sustained during this time Proofreading and repairing DNA DNA polymerases proofread newly made DNA, replacing any incorrect nucleotides In mismatch repair of DNA, repair enzymes correct errors in base pairing Now and then a mutation does occur
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