Ras gene

• Ras protein is a component of a signal-transduction pathway -> activates a protein that stimulates cell cycle to promote growth in the organism
• Signal transduction pathway: a series of chemical reactions in the cell that conveys signals from the external environment of the cell to the DNA in the nucleus
• Ras protein -> G-protein that relays a growth signal from a growth factor receptor to a cascade of protein kinases
• end of pathway: synthesis of protein that stimulates cell cycle
• Cell cycle stimulating pathway:

  1. A growth factor binds to its receptor and activates the receptor
  2. The signal is relayed to Ras protein -> activated by binding of GTP
  3. activated RAs protein passes the signal to a series of protein kinases
  4. last protein kinase activates a transcription factor (an activator) that initiates transcription of one or more genes that code for proteins that stimulate the cell cycle

  results in : increased rate of mitosis and cell division occurs at the faster rate
• Ras gene MUTATED -> oncogene produces a hyperactive Ras protein

  • can activate protein kinase even in absence of growth factor
  • genes that stimulate the cell cycle are transcribed continuously -> uncontrolled cell division