Homework9Solution - without being folded in some way Why or...

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Biology 214/414 Homework #9 Due 10-23-09 Recall that the amount of DNA in one complete nucleosome is the amount of DNA in the core particle (always 146 bp) plus that in the linker (which can vary from 8-114 bp, depending on the species, cell type, etc.). Human chromosome 21 (the one involved in Down’s syndrome) is 45 million bp long. If the average linker length in the nucleosomes in this chromosome is 50 bp, each nucleosome is 6 nm tall, and all the nucleosomes in chromosome 21 are stacked on top of each other in one tremendously tall stack, how tall would this stack of nucleosomes be? Would it be able to fit in a typical human nucleus
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Unformatted text preview: without being folded in some way? Why or why not? The amount of DNA in a core particle is 146-147 bp; for simplicity’s sake, let’s call it 146 bp. Then the length of DNA in the average nucleosome is 146 + 50 = 196 bp. Thus, the total number of nucleosomes in one copy of chromosome 21 is (4.5E7 bp)/(1.96E2 bp/nucleosome) = 2.3E5. If each is 6 nm tall, then the length of the entire “stack” is (6 nm/nucleosome)(2.3E5 nucleosomes) = 1.38E6 nm = 1.38 million nm =1380 μ m. A typical human nucleus is about 5 m in diameter, so that considerable folding in addition to that in the nucleosomes themselves is essential....
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