24-25_Lieb_Euk_txn_chrom_II-PEV-DC_combined

24-25_Lieb_Euk_txn_chrom_II-PEV-DC_combined - Regulation of...

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Regulation of Eukaryotic Transcription II:  Chromatin J. Lieb Luger et al, Nature 1997 The structure of the nucleosome Reading: 11: 394-412 
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Molecular Biology Occurs at an Unfamiliar Scale If a mouse  were the size of Chapel Hill (10 miles)  a cell would be about the size of a volleyball (8 inches in diameter)   a gene would be on average about an inch long.  genome would be 80 MILES long.  About 10 14  cells in a human body (100 trillion). And 20 times that number of  bacteria! If a cell  were the size of Chapel Hill (10 miles):    an average protein would be the size of a minivan (10 feet)   an average gene would be about 1.5 miles long but the strand of  DNA would only be a few feet wide.   Now, the genome would be ~3 million miles long!  125 times around the earth.
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Every cell contains 2 meters of DNA 10 trillion cells/body = 20 trillion meters 70 round trips from the earth to the sun How is this possible? Nucleus: 6 millionths of a meter in diameter occupies about 10% of the cell 2 nm 2.06 m
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Not like this ! More like this
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The DNA within cells is NOT naked!
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Nucleosomes are spools of DNA
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DNA is Packaged into Chromatin
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Chromatin is organized by many levels of folding or packing Compaction ratio: 10,000
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One model for a 30-nm fiber
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Efficient packing makes it difficult to retrieve information Library Gene
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DNA binding motif DNA binding protein Nucleosome Library X OFF ON Chromatin Being read Not being read To access information encoded in DNA, DNA must be unpacked
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heterochromatin cytology: stains brightly genetics: suppresses gene expression molecular: rich in satellite sequences chromosomal: centromeres of higher eukaryotes are within heterochromatin Drosophila Chromosomes Cytologically, there are two main types of Chromatin:   Heterochromatin and Euchromatin Euchromatin: “Open”, associated with expressed genes
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24-25_Lieb_Euk_txn_chrom_II-PEV-DC_combined - Regulation of...

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