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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12 - Eukaryotic chromosome organization Chromatin -...

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