Epigenetics

• Epigenetics

  • Means “Beyond genetics”
  • Refers to factors that make genes more or less likely yo be transcribed and translated
  • While the phenotype changes, the DNA sequence itself remains unchanged
• Chromosome Structure

  • Are made up from DNA which has been condensed
  • The DNA wraps around special proteins called histones, which then coil up and coil up until a chromosome is formed.
  • The Histones decide the shape of the chromosome and which genes are exposed for transcription
• DNA Methylation

  • The addition of a methyl group to a cytosine base
  • DNA polymerase cannot read and bind a guanine base to a methylated cytosine, so transcription does not occur
  • This causes silencing of the gene and stops the protein from being produced (altering phenotype
• • This can be a good thing as we need to turn off genes that aren't required by cells during cell differentiation and specialisation.
  • Certain genes need to be silenced so that normal development can occur 
  • An important source of methyl groups if folate, which prevent Spina Bifida by methylating genes responsible for spinal cord development.
• Sources of Methyl Groups.

  • Diet
  • Stress
  • Heavy metals
  • Pesticides
  • Tobacco smoke
  • Car exhaust
• Histone Acetylation

  • The addition of an acetyl group to a histone
  • Causes DNA to toil more loosely around histones, makes more genes accessible for transcription
  • The causes expression of the gene and more of the protein is produced (altering phenotype).
  • Deacetylation is removal of an acetyl group from a histone
  • Causes DNA to toil more tightly around histones, making then unavailable for transcription
  • This causes decreases expression of the gene and less of the protein is produced (altering phenotype)
• Sources of Acetyl Groups

  • Diet
  • Stress
  • Radiation
  • Pesticides
  • Tobacco smoke
  • Neurotransmitters