regulation of transcription/lation

• ACTIVATOR


  Activate genes
• REPRESSOR


  Deactivate genes
• How do activators work


  bind to promotor regions which stimulates RNA polymerase

  allows transcription of gene
• Oestrogen only affects target cells. Explain why oestrogen does not affect other cells in the body.

  other cells don't contain the oestrogen receptors
• Use Figure 2 to suggest how endoxifen reduces the growth rate of these breast tumours.

  (figure 2 shows 2 pictures of molecules endoxifen and oestrogen that are similar shapes)

  Similar shape to oestrogen so binds to receptor preventing oestrogen from binding

  this means receptor won't be activated and transcription won't happen
• How do repressors work?

  deactivate genes by binding to genes and preventing RNA polymerase from being stimulated therefore stopping transcription of gene
•  This siRNA would only affect gene expression in cells infected with HIV.

  Suggest two reasons why

  • Only infected cells have HIV protein on surface - So siRNA can only enter these cells;
  • siRNA base sequence is complementary / specific to one mRNA. Only infected cells will contain this mrna
• Explain why steroid hormones can rapidly enter a cell by passing through its cell-surface membrane.

  lipid soluble so can diffuse through phospholipid bilayer
• In the cytoplasm, testosterone binds to a specific androgen receptor (AR).

  An AR is a protein.

  Suggest and explain why testosterone binds to a specific AR

  Has a specific tertiary structure

  structures are complementary
• The binding of testosterone to an AR changes the shape of the AR. This AR molecule now enters the nucleus and stimulates gene expression.

  Suggest how the AR could stimulate gene expression.

  AR is a transcription factor

  binds to promotor region and stimulates rna polymerase
• RNAI


  small strands of rna that bind to mrna to form double stranded structures
• SiRNA

  • associated with proteins in cytoplasm and unwinds
  • single strand binds to complementary target mRNA (siRNA specific to this )
  • Proteins bound to siRNA chop up mRNA into fragments meaning it can no longer be transcribed
  • fragments transported to processing body where they will be degraded
• miRNA

  • miRNA not fully complementary to mRNA therefore less specific and can target multiple mRNA molecules
  • binds to proteins in cytoplasm and forms complex which binds to the target mRNA
  • This blocks ribosomes from translating mRNA
  • mRNA moved to processing body where it is either stored or degraded
•  Explain why the antibody binds to the transcription factor.

  Transcriptional factor has a specific/tertiary structure

  antibody is complementary to this structure