Regulation of transcription and translation

• Describe transcriptional factors

  • Transcriptional factors are proteins that control gene expression
  • They are found in the cytoplasm but can move into the nucleus when activated
  • They bind to promoter regions of their target genes
  • This either:
  • Allows RNA polymerase to bind and begin transcription of the gene
  • Inhibits RNA polymerase from binding so transcription can't occur
• Describe the role of oestrogen in regulating transcription

  1. Oestrogen simply diffuses across the cell surface membrane as it's lipid soluble
  2. Oestrogen binds to a transcriptional factor in cytoplasm, causing it to change its shape and expose the DNA binding site
  3. The transcriptional factor move into the nucleus and binds to the promoter region of the proto-oncogene
  4. This allows RNA polymerase to bind, and transcription of the proto-oncogene begins
• Describe oestrogen related to cancer

  1. Oestrogen is mostly produced by the ovaries before menopause
  2. After the menopause, the ovaries stop producing oestrogen and breast tissue takes over instead
  3. This higher concentration of oestrogen in breast tissue activating proto-oncogenes increases the risk of breast cancer developing
• Define epigenetics

  Heritable changes to gene function without changes to the DNA base sequence
• Describe epigenetics

  • DNA is wrapped around histones
  • If the DNA and histones are loosely packed, transcription factors can access promoter regions and genes can be expressed (switched on)
  • If the DNA and histones are tightly packed, transcription factors can access promoter regions and genes are not expressed (switched off)
  • The association of chemical tags, methyl and acetyl groups is what determines how tightly packed the DNA and histones are
• Describe methylation

  1. Methyl groups bind to cytosine bases on DNA
  2. This attracts the histone proteins together which tightly packs the DNA and histones
  3. Transcription factors cannot bind to promoter regions
  4. RNA polymerase cannot stimulate transcription, so genes are not expressed
• Describe deacetylation

  1. Acetyl groups are removed from histone tails which uncovers their positive charge
  2. Histone tails are now attracted to negatively charged phosphate groups on DNA, which tightly packs the histones and DNA
  3. Transcription factors cannot bind to promoter regions
  4. RNA polymerase cannot stimulate transcription so genes are not expressed
• Describe RNA interference

  1. Cells produce double stranded RNA (dsRNA)
  2. An enzyme called DICER hydrolyses dsRNA into smaller interfering RNA (siRNA)
  3. The siRNA can bind to a specific mRNA through complementary base pairing
  4. DICER cuts the mRNA into small fragments to prevent its translation