• After the ligand binds, the intracellular domain of the receptor protein changes shape, initiating transduction of the signal by converting it into a form that causes cell response
    • Main Idea: molecules interact with each other to relay/amplify signal


  • Small, non-protein molecules that spread through cell via diffusion and relay/amplify the intracellular signal

 2nd Messenger: Cyclic AMP (cAMP)

  • Created using adenylyl cyclase by cutting ATP and two phosphates
    • Can activate protein kinase→ Cell response

2nd messenger: Ca+

  • Ca+ levels stimulate cellular response
  • Cell regulates concentration by actively transporting into ER and mitochondria

Signaling Cascade

  • Many signal transduction pathways include protein modification and phosphorylation cascades
  • Kinase cascade or phosphorylation cascade: Series of enzymatic reactions where a kinase enzyme phosphorylates molecules which phosphorylates another molecule, etc.
    • Benefits: amplify so that small signal made bigger, better regulation/control
  • Signaling cascades relay signals from receptors to cell targets → amplify incoming signals → result in appropriate cell response
  • Scaffold Proteins: large relay proteins attached to each other which improve efficiency of signaling cascade by holding participating enzymes in close proximity
    • Scaffolding also used to keep members of one signaling cascade isolated from members of another cascade