Cell Signaling and Signal Transduction PP Notes

Signal transduction is the process by which extracellular messages are translated into intracellular responses.

There are two routes by which this can take place:

  1. A trans-membrane receptor receives a ligand from a signaling cell then activates an effector. The effector then generates a secondary messenger which activates a protein.

  2. The trans-membrane receptor activates the protein without an effector or secondary messenger via its cytosolic side


Changes to proteins are accomplished by either kinases via phosphorylation or phosphatases using de-phosphorylation. This has a number of effects:

  • activation/inactivation of proteins

  • increase/decrease protein interaction

  • promote/prevent protein movement

  • initiate protein degradation


Signaling molecles

  • Small molecules

    • glutamate, acetylcholine, glycine, epinephrine, dopamine

  • Steroids

    • cholesterol derivatives

    • regulate sexual differentiation, pregnancy, carbohydrate metabolism

  • Eiconsanoids

    • 20 carbon, nonpolar, arachdonic acid derivatives

    • regulate pain, inflammation, blood pressure and clotting

  • Polypeptides

    • growth hormone, insulin


Receptors

G Protein-coupled receptors (GPCRs)

  • bind an extracellular ligand to activate a membrane protein called G-protein

  • G-protein is guanine nucleotide-binding protein

    • may be monomeric or heterotrimeric (alpha, beta, gamma)

    • Can bind to both GTP and GDP