BIOL 2040 Lecture Notes - Lecture 22: Chromatin Immunoprecipitation, Histone Code, Sister Chromatids
Document Summary
In relation to inheritance, these need to be preserved in mitosis: Replication is semi-conservative, once replicated it exists briefly as two sister chromatids which are only half methylated (hemi-methylated). Dna methyl transferase then adds the correct methyl groups diagonally (due to antiparallel structure) to the newly replicated. Histone code: refers to modifications can come in different flavours ; different mods at different sites. This tells you why we have so many antibodies for different histones. Histones exist as an octamer ( dimer of two tetramers). Nucleosome: dna + histone (**remember 147bp to wrap around histones, 80bp between them; so for 1000 bp, approximately 4 histones will be present) Only half of nucleosome (4 histones) on newly replicated dna have histone code. Methylation pattern differences exist between different organs. Epigenome differs between cell types; within the same organ epigenome is basically the same. All liver cells are daughters of previous liver cells.