epigenetic control

• epigenetic control:

  • determines if gene is transcribed and translated
  • works through attachment/removal of chemical groups to DNA or histones
  • doesn't alter base sequence of dna
  • alters how easily enzymes and transcription proteins bind to DNA
  • can occur in response to changes in environment
• inheritance of epigenetic changes:

  • DNA base sequence is inherited from parents
  • most epigenetic marks are removed but some can be passed onto offspring
  • so expression of some genes in offspring can be affected by environmental changes that affected parents
• methlyation of dna (epigenetics):

  • a methyl group is an example of a genetic mark
  • always attaches at a CpG site, where cytosine and guanine are next to each other and attached by a phosphodiester bond
  • increased methylation changes dna structure so transcription machinery can not interact with the gene so it is not expressed
• acetylation of histones:

  • acetyl (epigenetic mark) attaches to or removes from histones
  • when histones are acetylated the chromatin is less condensed, so the proteins and enzymes can access and transcribe the DNA
  • deacetylation condenses the chromatin so transcription machinery can not access the DNA so it is not transcribed
  • histone deacetylase enzymes remove the acetyl groups
• development of epigenetic diseases:

  • fragile x syndrome is caused by a heritable mutation on the X chromosome
  • results in DNA sequence CGG being repeated more than usual
  • lots more CpG sites to bind to
  • increased methylation switches gene off
  • protein isn't produced causing symptoms
• treatment of epigenetic diseases:

  • epigenetic changes are reversible
  • drugs that stop DNA methylation can prevent genes being switched off
  • HDAC inhibitors prevent removal of acetyl groups so DNA does not condense and can be transcribed
  • the drugs need to be very specific as epigenetic changes play a role in lots of normal cellular processes