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BIO240 Lecture 3

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Jennifer Harris

Lecture 3 Transcriptional Regulation 1In the last lecture we took a look at 2 chimpswe talked about the role that the transcriptome plays in giving rise to the differences bw those 2 chimpsConsidered a problem with regards to the generation of that transcriptome the diversity of RNA transcripts that one finds in an organism that defines the organism itself different tissue types different cell types or different cells in different points in time or under different conditionsProblem that we had to deal with is this the challenge that the genome has to deal withnot such a big challenge with procaryotes but big challenge with eucaryotesLast lecture considered a model that would allow one to accommodate all of those factors so that one could have a tightly compressed genome within the nucleus but access it at appropriate points in time or in appropriate cells to give rise to differences in the transcriptomeIn circumstances where one does not need to access the info contained in the genome its tightly condensed within the chromosomeheterochromatin But then when genes need to be accessed for the process of transcription theyre decondensed made into euchromatin Take a look at the interplay again bw genome organizationthe regulation of transcription The idea is that we have to access the 4 letter code in the DNA and the idea that the chromatin has to be remodeled and exposed to allow for these RNA polymerase to give them access to the chromosomes Last lecture about transcription of RNA how they were made and now a little more about regulation How is this orchestrated How is it controlled How are specific regions of the genome regulated in such a way that only those genes are expressed Movie organization of nucleosomes octameric core comprising histone proteinstheir interactions with DNA Wavy bits are histone tails DNA is going to interact with the histone proteins Can see the tails whipping off the endwaving outthats the nucleosome with the histone tails wagging off around Important point with regards to those histone tails the 8 histones pairs of 4 different histones present in the nucleosome core 2A 2B 34 have tails that are accessiblecan be posttranslationally modified The chromatin is remodeled for the purposes of gene expression how is this orchestrated Missing slide showing DNA that is going to be wrapped around histone proteins The histones have tails whipping around and what you see is nucleosome with DNA wrapped around and then the nucleosomes are assembling into the 30 nm chromatin fibre
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