BIOL308 Study Guide - Trp Operon, Tata-Binding Protein, Rna Polymerase Iii
13 Jun 2013
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Document Summary
Histones have n terminal tails of 20-40 aa which contain positively charged lysine groups. When lysine is acetylated (by acetyle transferrase aka histone acetylases. Since dna is negatively charged and the neutralization effect of the positive lysine is now lost, repulsion occurs leading to the formation of a less condensed chromatin (euchromatin). Binding sites are now exposed and transcription is activated. (gtfs bind followed by rnap) Deacetylation on the other hand, increases the positive charge on the lysine residues leading to lesser repulsion between the dna strands and therefore, a more condensed heterochromatin structure. Binding sites are now inaccessible for tfs and transcription is inhibited. N. b: deacetylases are present in co-repressor complexes and coactivators have hat activity: describe the role of chromatin remodelling complexes in regulation of transcription. Histone acetylation isn"t sufficient for activation; nucleosomes are still intact and have to be repositioned to expose the promoter elements.
