GENE 320 Lecture Notes - Lecture 12: Open Reading Frame, Phosphodiester Bond, Pyrimidine
Document Summary
During interphase chromosomes are decondensing and dispersing throughout the nucleus. Cell division condenses the chromatin back together into visible chromosomes. Histones are positively charged proteins associated with chromosomal dna in eukaryotes. They also contain large amounts of lysine and arginine. Makes electrostatic bonding to negatively charged phosphate possible. Main types: h1, h2a, h2b, h3, and h4. Allow for the expression (loose) or silencing (tight) of chromosome gene sequences. Twist and turns of dna superhelix encircle histones. Unstructured histone tails - stick out, accessible to modi cations that control the level of packing. This tails control how tight or loose the chromatin packing with be. To allow replication and gene expression, chromatin must: relax compact structure expose regions of dna to regulatory proteins have a reversal mechanism for inactivity. Chemical modi cations for genetic function: acetylation - allows for expression - euchromatin - uncoiled and active.
