01:447:380 Lecture Notes - Lecture 11: Heterochromatin, Dna Replication, Gene Expression
Document Summary
Dna packaging: prokaryotes proteins, formation of loops domains: each loop is held in place by dna binding, supercoiling: happens within loop domains. Can be constitutive (always condensed) or facultative (condensed at certain times) Packaging changes during cell cycle (depends on gene expression) Beads (1) simples level of chromatin structure (2) dna double helix wraps around twice on proteins (3) visible under low salt condition. Nucleosomes (1) contains histone proteins (2) small, positively charged. Dna: two ways dna methylation down-regulated gene expression. Methyl group in major groove prevents binding of proteins that stimulate transcription. Important for turning on gene expression: histone modification, heritable. Silences expression of dnmt3 gene (codes for methyltransferase enzyme) Overall genome is less methylated increased gene expression. Express dnmt3 gene so genome is more methylated: x-inactivation. Random event that happens early in development. Contains several important genes: x-ist (x-inactivation-specific transcript) Binds x-chromosome from which it was made. Methylate histones to turn off gene expression.
