Epigenetics

• Inheritable change to gene function without change to the DNA base sequence.
• These inheritable changes are caused by changes in the gene's environment that inhibit transcription by...

  • increased methylation of DNA
  • decreased acetylation of histones
• Methylation

  Repeated CpG sequences are common in the DNA near gene promotors. The presence of repeated CpG sequences near a gene promotor inhibits the activity of the enzyme RNA polymerase. As a result, the affected gene cannot be transcribed - it is effectively silenced.
• Acetylation

  Histone molecules have side branches, or 'tails'. The tails can be acetylated, i.e. an acetyl group is transferred to it from acetylcoA. When acetylated, the histones become more loosely packed thus allows RNA polymerase to bind to the promotor region more easily in order to transcribe and therefore express the gene.
• A decrease in methylation of protooncogenes and an increase in methylation of tumour suppressor genes can lead to cancer.