12 - Eukaryotic chromosome organization • Chromatin...

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Unformatted text preview: Eukaryotic chromosome organization • Chromatin - condensed / open • Nucleosome structure • Histones • heterochromatin & euchromatin Bacterial chromosome Packing of DNA is crucial • must prevent knotting or tangling of long DNA molecules • must also permit specific DNA sequences to be available for various cellular processes (ex. transcription, DNA replication, DNA repair) “linker” DNA nucleosome DNA packaged into nucleosomes (DNA + histones) Histones: •Small basic proteins (rich in positively charged amino acids) •Interact with negatively charged phosphate groups in DNA • octameric - 2 copies each of H2A, H2B, H3 & H4 • histone core is disk-shaped Nucleosome is a complex of 8 histones http://biology.kenyon.edu/courses/biol114/Chap01/chrom_struct.html H1: • fifth major histone • binds DNA as it enters & exits nucleosome core Structure of a nucleosome based on X-ray crystallography DNA covers much of the histone protein on the lateral surface, but histone proteins can interact on top and bottom and stack together like “coins” “histone code” • Histone post-translational modifications influence chromatin structure and function Less acetylated (hypo-) More acetylated (hyper-) •Formation of heterochromatin •Higher eukaryotes also have co- repressor complexes that contain HMT subunits •Ex. •HP1 •chromodomain Heterochromatin • condensed • “inactive” • centromere • telomere Euchromatin • less condensed • “active” Hetero- vs. Eu -chromatin Important concept:...
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This note was uploaded on 03/31/2010 for the course BIMM bimm 100 taught by Professor Dr.sato during the Winter '08 term at UCSD.

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12 - Eukaryotic chromosome organization • Chromatin...

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