epigenetics 1

• • control of gene expression by factors other than DNA sequence
  • switcging on or off of genes without changing genetic code
• chromatin

  • DNA wrapped around histone proteins
  • can be chemically modified via methylation or acetylation
  • these modification are epigenetic tags- all tags in organism called genome
  • epigenome undergoes changes due to enviro factors eg smoking, stress
• methylation

  • methyl group added to cytosine bases of DNA
  • suppresses the transcription of affected gene, inhibting the binding of TFs
  • gene is repressed/inactivated
• acetylation

  • acetyl group added to histone proteins
  • removes positive ions and removes bond between histone protein and DNA- DNA wrapped less tightly
  • RNA polymerase and TFs bind more easily thus gene expression can occur- gene is activated
• epigenome is heritable- when cell divides epigenetic changes may be passed on to daughter cells