BIOL1020 Lecture Notes - Lecture 11: Histone Methylation, Methyl Group, Chromatin
Document Summary
Every cell in a eukaryote contains the same dna. Not all genes are required at all times, in all cell types and under different environmental conditions. Certain chemical modifications to chromatin - both to the histone proteins of the nucleosomes around which dna is wrapped and to the nucleotides that make up that dna - can influence chromatin structure and gene expression. Histone acetylation (addition of acetyl group) is associated with active chromatin. Histone methylation (addition of methyl group) leads to the condensation of chromatin, which reduces transcription. Dna methylation occurs when enzymes directly methylate dna bases, usually cytosine. Genes that are heavily methylated are usually not expressed. Removal of these methyl groups can serve to activate these genes. Methyl groups added to c base, when there is a cg sequence (called. Genes within heterochromatin, which is highly condensed, are usually not expressed.
