Signal Regulation and Contact Activation

Response and Signal Regulation

Phosphorylation Cascade

  • Amplification

    • Description: The process where one enzyme activates multiple other molecules, leading to a significant increase in signal strength.

  • Specificity

    • Example: Acetylcholine (ACh) interacts with different receptors in various cells to induce specific responses.

  • Efficiency

    • Folding Proteins: Proper protein structure promotes efficient signaling.

  • Termination:

    1. Degrade/Remove Ligand: Signals must be terminated to prevent constant activation.
    2. Block Receptor: Inhibition of receptors helps stop the signal.
    3. Apoptosis: Programmed cell death can be a response to excessive or inappropriate signaling.

Contact Activation

  • Key Components:

    • Prekallikrein → Kallikrein → Factor XII → Factor XIIa
    • Coagulation Cascade:
    • Activated by thrombin and tissue factor leading to fibrin formation.

  • Zymogens and Activation:

    • Zymogens are inactive precursors activated by proteolytic cleavage, e.g., Prothrombin → Thrombin → Fibrin Polymer.
    • Activation Pathway:
    • Enzyme #1 activates zymogen #2 (1 molecule activates 100 targets).
    • Enzyme #2 acts on zymogen #3 (100 molecules can activate 10,000).
    • Enzyme #3 activates zymogen #4 (10,000 molecules can produce 1,000,000 activated molecules).

Signal Regulation: Specificity

  • Example of Specific Response:
    • Acetylcholine:
    • Heart Muscle Cell: Decreased rate and force of contraction.
    • Skeletal Muscle Cell: Induces contraction.
    • Salivary Gland Cell: Stimulates secretion.
  • Esrogen Signaling Pathway:
    • Involves various intermediary proteins and cascades contributing to gene expression and cell signaling.
    • Components such as GPCR, SHC, Ras, PI3K, ERK, and NF-kB are crucial in signaling pathways.

Signal Regulation: Efficiency

  • Scaffold Proteins:
    • Organize the signaling components facilitating more efficient communication
    • Example: Inactive intracellular signaling proteins activated by receptor engagement can stimulate downstream signals.
  • Extracellular and Cytosol Interaction: The binding of signaling molecules to receptors on the cell surface triggers a cascade of intracellular signaling events leading to cellular responses.