Spring 09 lecture 07

Spring 09 lecture 07 - Signing for midterms: Signing lists...

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11 Signing for midterms : Signing lists are posted on the web site Signing has to be done by June 8 (read the info) You can sign for only one of two offered dates (June 15 or June 22)
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22 Eukaryotic chromatin : eukaryotic genomes organized into chromosomes each chromosome contains single, linear DNA molecule , wrapped up and packed with the help of specific proteins and protein complexes S nucleoprotein material of eukaryotic chromosome is called chromatin ; organized into chromatin fibers by dark field electron microscopy, fiber structure of a chromosome resembles “beads on a string” (Lewin, 2006. Fig. 29.1)
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33 Chromatin Organization “Beads on a string”: The fundamental unit of organization of the chromatin fiber is nucleosome Each nucleosome contains a core particle of histone proteins which are wrapped by DNA. Also : nonhistone proteins are involved and important for chromatin organization http://www.johnkyrk.com/chromosomestructure.html
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44 Chromatin Organization: Histones Present in all eukaryotic nuclei Small proteins rich in lysine and arginine (at normal pH their “extra” amino groups become NH3+) – basic proteins Interact with DNA through electrostatic interactions Five major types H1, H2A, H2B, H3 and H4 H2A, H2B, H3 and H4 form a complex of 8 proteins (octet) (Lewin, 2006. Fig.
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55 Nucleosome = octet of histones and wrapped DNA DNA (147 bp) wraps around octet approximately 1.65 times H1 associates with DNA and octet in linker region – binds two distinct regions of the DNA duplex Chromatin Organization: Nucleosomes
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66 Size of DNA that wraps around octet– can be analyzed/estimated by partial digestion with DNase I (nuclease) Size of the linker – variable - depending on DNase concentration
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77 Chromatin Organization: Nucleosomes (cont.) Core histones alone : ~ 4-fold repression Core histones + H1 : 25- to 100-fold repression Nucleosome is 10 (11) nm in diameter 10 nm fiber is packed into a 30 nm diameter fiber Lower or higher salt concentration during isolation - different forms ( 10 nm nucleosomes - beads or more condensed 30 nm fibers , respectively). Why?
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This note was uploaded on 08/03/2009 for the course BIOL BIOL308 taught by Professor Miskovic during the Spring '09 term at Waterloo.

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Spring 09 lecture 07 - Signing for midterms: Signing lists...

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