3_6 - lecture 3/6/07 Packaging 1.) 10nm fiber Euchromatin-...

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lecture 3/6/07 Packaging 1.) 10nm fiber Euchromatin- goes through cycles where it is condensed for cell division (so the chromosomes don’t get tangled up) and then relatively decondensed to allow for transcription. It is the multi-layered “packaging” that makes this possible. DNA is first wrapped around a group of histones (H2A, H2B, H3, and H4- 2 of each kind makes the octomer) . The DNA wrapped around the histones makes up the nucleosome. 8 histone proteins and the DNA. (“Beads on a string”) This is the first level of “packaging”- 10 nm fiber. The diameter across the nucleosome is approximately 10 nm. Book calls it something else, but this is the more common term. Where is DNA binding (non-specific)? The backbone. The negative charge of the phosphates is where the positively charged histones bind. This is what helps the histones stay bound to DNA. 2.) Next, the 10nm fiber folds over and over again. This new folded fiber has a new diameter of 30 nm, so it is called the 30 nm fiber. The histone H1 holds the chromatin in the 30 nm fiber configuration. 3.) Radial loop domains- protein filament that runs across them and anchors the bottom of each loop (this is how they remain in the loopy structure). The filament is not composed of histones; some non-histone proteins participate in packaging! This is the form interphase euchromatin is found in!
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3_6 - lecture 3/6/07 Packaging 1.) 10nm fiber Euchromatin-...

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