What are the three stages of cell signaling?
Reception
Transduction
Response
Reception
The target cell’s detection of a signal molecule coming from outside the cell
Transduction
The conversion of the signal to a form that can bring about a specific cellular response
Response
The specific cellular response to the signal molecule
Receptors are found in two places. Where are they found?
Intracellular receptors
Plasma membrane receptors
Intracellular receptors
Found inside the plasma membrane in the cytoplasm nucleus. Signal molecule must cross the plasma membrane and therefore must be hydrophobic, like the steroid hormone testosterone
Plasma membrane receptors
Located on the plasma membrane, bind to water soluble ligands
What does a G protein bind to?
G protein-coupled receptor
Receptor tyrosine kinases
A second type of membrane protein
Phosphorylation cascade
Signal transduction pathways are usually a multi step one, the possibility of greater amplifying the signal exists. At each step enzymes (protein kinases) phosphorylate and activate many proteins on the next level.
This greatly enhances the signal, allowing for a large cellular response.
Many signaling pathways involve small, nonprotein water-soluble molecules or ions called
Second messengers
What are the two types of second messengers?
Calcium ions and cyclic AMP
What do second messengers do?
Once activated, can initiate a phosphorylation cascade resulting in a cellular response.
Apoptosis
A program of controlled cell suicide
(Triggered by signals that activate cascade of “suicide” proteins in the cells)
Is a normal part of development in vertebrates and is essential for normal nervous system, for operation of the immune system, and normal morphogenesis of hands and feet in humans.