Transcriptional and translational factors

• Why are transcriptional factors needed?

  To prevent cellular resources being wasted
• What percentage of genes are expressed by human cells?

  3-5%
• What do transcriptional factors do?

  Either stop or promote transcription
• What are transcriptional factors?

  Proteins which move in from the cytoplasm and bind to DNA
• Where are promoters found?

  At the start of their target gene
• What do promoters do?

  Control the rate of transcription
• Which enzyme can promoters activate?

  RNA polymerase
• What are repressors?

  Proteins that bind to a target gene and inhibit transcription
• Which enzyme can repressors prevent?

  RNA polymerase
• How has oestrogen adapted for its function?

  • Lipid soluble
  • Can switch on a gene
  • Complementary in shape to receptor molecules
• How does oestrogen effect the receptor molecule?

  • Changes the shape
  • Complex moves from the cytoplasm into the nucleus
  • Binds to DNA sites at the start of a target gene
  • Complex acts as an activator of transcription
• What is gene expression affected by?

  RNA interference (RNAi)
• What is RNAi?

  Small double-stranded RNA molecules stop mRNA from target genes being translated into proteins
• What molecules are involved in RNAi?

  siRNA (small interfering RNA) and miRNA (micro RNA)
• How does siRNA work?

  1. Combines with enzyme
  2. Guides enzyme to mRNA by pairing up with complementary bases
  3. Enzyme cuts mRNA into small pieces
  4. mRNA cannot be translated
  5. Gene is not expressed
• What is the potential for siRNA?

  • Can be used to identify the role of genes in a biological pathway
  • Genes causing certain diseases can be blocked so that the disease is not expressed