1. B. Signal Transduction Pathway (cell signaling)
1. Process by which a signal on a cell surface is converted into a specific cellular response
Multistep process
Relies on plasma membrane proteins as receptors
2. Three stages:
Reception
Transduction
response

2. 1. Reception- Target cell’s detection of a signal coming from outside the cell
“Detection “– binding of a signal (ligand) to a cell protein (receptor) at the cell’s surface
Binding causes “conformational change” in receptor
Receptor becomes activated to work with another molecule
3 types of receptors (G-protein receptors, ion channel receptors, kinase receptors

3. 2. Transduction – converts the signal to a form that can bring about a specific cellular response
Usually involves a series of changes in a sequence of molecules
relay molecules - protein kinases that “phosphorylate” the next molecule
“cascade of phosphorylation” activates proteins in a step-by-step manner
Secondary messengers – small, non-protein, water soluble molecules that can readily spread through the cell by diffusion- protein kinases (Ex. cAMP, cGMP, Ca+ ions)

4. 3. Response – two ways
1. Can regulate activities in the cytoplasm i.e. enzyme activation
2. Can activate specific genes by altering transcription factors