HO-20 - BIO 320 lecture 20 Reading: Ch 10.2, Ch 13, Ch 14...

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BIO 320 lecture 20 Reading: Ch 10.2, Ch 13, Ch 14 pp 509 - 514 H2A+H2B +H3+H4 2x Many nucleosomes and linking DNA = 10 nm fiber + histone H1, and coil = 30nm fiber Eukaryotic chromatin and chromosomes 4.5 cm - length of DNA in a medium- sized human chromosome Organization of eukaryotic chromatin Furthermore. .. the 2 meters of DNA in the diploid human genome must be packaged into a 5 μ m (5 x 10 -6 m) nucleus – while still being accessible for transcription and replication. histone octamer 145bp DNA coiled twice + core nucleosome Main protein component of chromatin: histones - basic (lys, arg-rich), highly conserved proteins. Higher-order loops and other structures = Nucleosomes and transcription initiation To be transcribed, chromatin must be partly unwound - possibly to a10nm fiber. RNA polymerase can transcribe around nucleosomes, but histones may compete with transcription factors for access to promoters and enhancers (positive regulatory regions). Nucleases can be used to assess the degree to which DNA is protected from digestion by packing in nucleosomes. The transcription-repressing properties of nucleosomes can be reduced by histone acetylation . Euchromatin , containing expressed genes, is dispersed in interphase and condenses into chromosomes at mitotic prophase. Heterochromatin : remains condensed throughout the cell cycle. Typically, gene-poor regions near the centromere and telomeres are heterochromatic. Non-histone proteins form a nuclear matrix that supports the chromatin. DNA topoisomerase II at matrix attachment sites may help unwind DNA loops for replication. Chromatin condensation: euchromatin and heterochromatin.
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This note was uploaded on 06/03/2008 for the course BIO 320 taught by Professor N/a during the Spring '08 term at SUNY Stony Brook.

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HO-20 - BIO 320 lecture 20 Reading: Ch 10.2, Ch 13, Ch 14...

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