AP Syllabus focus:
‘After ligand binding, receptor shape change triggers cascades where enzymes and second messengers like cAMP amplify signals to produce strong cellular responses.’
Cells often respond to very low concentrations of external signals. Signal amplification and second messengers explain how a single ligand-binding event can trigger many intracellular events, producing a rapid, robust, and coordinated cellular response.
Core idea: amplification in signal transduction
Signal amplification occurs when one activated molecule causes the activation or production of many downstream molecules, increasing the magnitude of the response relative to the initial signal.
Amplification is most likely at steps involving:
Practice Questions
FAQ
Cells use microdomains formed by anchoring proteins that hold cAMP-producing enzymes, phosphodiesterases, and cAMP-sensitive targets close together.
This creates local cAMP “hotspots” and prevents widespread activation.
Benefit depends on matching response strength to context: high amplification increases sensitivity and speed.
Harm occurs if amplification outpaces shut-off mechanisms, causing inappropriate activation of downstream targets.
cAMP moves through the cytosol by diffusion.
Its spread is limited by rapid enzymatic breakdown (phosphodiesterases) and physical/structural barriers that compartmentalise the cytoplasm.
Not always. Some second messengers are produced (like cAMP), while others can be released from intracellular stores (for example, ions released from organelles).
Both strategies rapidly increase intracellular messenger concentration.
They can:
Inhibit second messenger synthesis enzymes
Inhibit degradation enzymes (prolonging signals)
Block binding of second messengers to their target proteins
These actions change signal strength and duration without altering ligand concentration.
