341lecture08sept25sakai

341lecture08sept25sakai - Cell Biology 341 Last lecture:...

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Cell Biology 341 Friday, Sept. 25, 2009 Today: chromatin changes structure during gene expression Next: chapter 6 on gene expression RNA polymerase Procaryotic initiation of transcription Tetranucleosome = Nature (London) volume 436, page 138- 141 (7 July 2005) Log into e-journals on the URI library website Last lecture: DNA packaging DNA molecules are too long to fit into the nucleus Mitotic chromosomes are the most highly compacted; interphase chromatin is at least 500-fold condensed The nucleus is surrounded by two membranes = nuclear envelope Nucleosomes are composed of 147 bp of DNA wrapped almost twice around 2 copies each of 4 core histones + 50 bp linker DNA associated with H1 Nucleosomes are packaged into tetranucleosomes and further coiled into the 30 nm fiber The 30 nm fiber is packaged into looped domains, and even further compacted at mitosis
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Chromatin structure changes during gene expression Interphase chromosomes contain regions of less condensed euchromatin in which the genes may be transcribed, and highly condensed heterochromatin regions, in which genes are silenced Heterochromatin is most abundant at the centromere, telomeres and points of attachment to the nuclear lamina Changes in chromatin structure involve c ovalent modification of histone tail domains, replacement of core histones with variant histones , and/or binding other non-histone proteins For example, acetylation of histone tails is correlated with
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341lecture08sept25sakai - Cell Biology 341 Last lecture:...

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