Regulation of transcription and translation

• In eukaryotes, transcription of target genes can be stimulated or inhibited when specific transcriptional factors move from the cytoplasm into the nucleus. The role of steroid hormones, oestrogen, in initiating transcription. ​​​
• How are genes transcribed?

  1. ​Transcription factors move from the cytoplasm to the DNA and bind to a specific base squence on DNA - called the promotor region.
  2. This allows the RNA polymerase to bind.
  3. The gene is transcribed - mRNA​ is made
  4. The mRNA can then be translated into the protein - the gene is expressed
• Oestrogen

  1. The lipid-soluble oestrogen diffuse through the phospholipid bilayer of target cell
  2. Binds to complementary shaped receptor in cytoplasm - this acts as a transcription factor
  3. This allows the receptor-oestrogen complex to bind to the DNA
  4. This allows transcription of the gene
• Oestrogen concentration and breast cancer

  A example of positive feedback

  • Post menopause the fat cells in the breasts produce more oestrogen
  • The oestrogen can control cell division by production of the proteins responsible for this
  • If the cell division becomes uncontrollable then this is now a malignant tumour - breast cancer
  • This, itself produces more oestrogen so the cancer grows faster
• Prevention of translation by siRNA

  • Small interefing strand which I complementary to the mRNA strand, binds to an enzyme and becomes a single strand.
  • Single mRNA strand binds to siRNA by complementary base pairing.
  • mRNA is hydrolysed, so it can't be translated into the protein.