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Lecture 19

Biology Lecture 19 Outcomes

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Biology 1002B
Tom Haffie

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Lecture 19 Polymerase only extend 3’ OHs Primase doesn’t need a 3’ OH that’s properly paired to add bases to RNA polymerases generally don’t require a properly paired 3’ Oh to start, DNA polymerases DO need one. Leading primer?  Is removed by DNA polymerase I  No 3’ OH available to replace the primer  DNA ends up being shorter  Cannot prevent that  Happens every time you replicate Telomerase  It adds telomeres to the ends of your chromosomes  Telomeres are just a repeated segment of DNA over and over again  No coding sequence in here  It makes DNA (kind of DNA polymerase)  All polymerases require a template  Telomerase has its own template (own bit of RNA that is uses as a template)  Extends the 3’ end  Making DNA from an RNA template is unusual THEN….  Once we increase the 3’ end, we can replicate backwards  Cells with short teomoeres have replicated a number of times  Can detect how od cells are from this length  Telomerase is mostly off in most cells most of the time o During gametogenesis, telomeres are added  Very short telomeres= trigger for apoptosis  Telomerase also doesn’t’ prevent cell from getting shorter, it just acts against it by making DNA longer so that it doesn’t matter if they shorten (the garbage added to the end doesn’t matter if it shortens)  Telomerase is a way to kill old cells that may contain mutations to lead to tumours o Intimate connection to tumours o Many tumours express telomerase when they shouldn’t be **so telomerase only acts during gametogenesis? No where else?? Telomerase extends chromosome ends- so they can shorten safely  Most cells replicate 50 times  DOES TELOMERES WORK ON BOTH SIDES??? Ames Test  Test based on salmonella bacteria  Bacteria are already
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