Epigenetics

• What are epigenetics?

  The idea that environmental factors can cause heritable changes in gene function by switching genes on or off. The base sequence of DNA is not changed
• What is the epigenome?


  The ‘tags’ that cover the DNA and histones

  They determine the shape of the DNA-histone complex
• When are genes switched on?

  When the DNA-histone complex is less condensed, so the DNA is accessible by transcription factors
• When are genes switched off?

  When the DNA-histone complex is more condensed so DNA is not accessible by transcription factors
• What are the two factors inhibiting transcription?

  Decreased acetylation

  Increased methylation
• What happens in decreased acetylation?


  An acetyl group is removed from a molecule, strengthening the association between the DNA and the histones so the DNA is not accessible to transcription factors
• What happens in increased methylation?


  A methyl group is added to the cytosine bases of a molecule

  This prevents transcription factors binding to DNA
• What can break down mRNA before translation?

  Small interfering RNA
• What does small interfering RNA do?


  Binds with an enzyme that then pairs with a section of mRNA. The enzyme then cuts the mRNA into smaller sections, stopping it from producing a polypeptide