Health Sciences 1001A/B Lecture 14: Regulation of Gene Expression 2

• School: Western University
• Department: Health Sciences
• Course: Health Sciences 1001A/B
• Professor: Jeannie Samuel

Document Summary

Histone modifications define chromatin: histones are modified by methylation, acetylation, phosphorylation, and other modifications, combinations of specific histone modifications define the function of local regions of chromatin. Histone acetylation: histones have a positive charge, allows binding to negatively charged dna, acetylation masks positive charge. Weakens dna-histone binding: reduces chromatin compaction, allows for transcription. Heterochromatin determined by histone methylation: hp1 is the key protein in forming mammalian heterochromatin, hp1 binds methylated histone h3, binding helps other hp1 proteins to bind, propagates heterochromatin formation. Cytosine methylation: methylation primarily occurs at cpg dinucleotides, methylated cytosines -> gene silencing, directly blocking transcription factors. Epigenetic modifications are heritable: cytosine methylation is maintained by a methylase, histone modifications are also maintained after replication. Epigenetic modifications change over time: ageing, diet, environmental exposures, drugs/ pharmaceuticals, twins that spent time in different environments - their time spent in different environments likely changed their epigenetic marks.