Cyclic AMP


The sequence of events for a protein hormone would be the following:
  1. The hormone binds to the extracellular portion of the receptor.
  2. Binding of the hormone to the receptor activates a G protein associated with the cytoplasmic C-terminal. This initiates the production of a "second messenger". The most common of these are cyclic AMP, (cAMP) and inositol 1,4,5-trisphosphate (IP3).
  3. The second messenger, in turn, initiates a series of intracellular events such as phosphorylation and activation of enzymes
    and release of Ca2+ stores within the cytoplasm
  4. In the case of cAMP, these enzymatic changes activate a transcription factor (CREB, cAMP response element binding protein)
  5. CREB binds to its response element in the promoters of genes that are able to respond to the hormone turning on gene transcription.
  6. The cell begins to produce the appropriate gene products in response to the hormonal signal it had received at its surface.