Signaling: Can You Hear Me Now?
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What makes receptors similar to enzymes?
Saturation kinetics; if there’s a high enough ligand concentration, the receptors can all become occupied
What is receptor affinity?
relationship between concentration of ligand in solution and the number of receptors occupied
What is high receptor affinity?
when almost all receptors are occupied at low ligand concentrations
What is low receptor affinity?
when it takes a high concentration of ligand for most receptors to be occupied
What is the dissociation constant (Kd)?
concentration of free ligand needed to produce a state at which half the receptors are occupied; quantitative value describing receptor affinity
What is the range of values for Kd?
10^-7 - 10^-10 M
What does a very low Kd mean?
the receptor has a high affinity for the ligand
What does a very high Kd mean?
the receptor has a low affinity for the ligand
What are agonists?
drugs that activate the receptor to which they bind
What are antagonists?
compounds that can bind to receptors without triggering the changes that occur when the normal ligand binds; can inhibit the receptor by preventing the normal second messenger from binding and activating it
What are the similarities and differences between an agonist and an antagonist?
Neither are the normal ligand to a receptor. However, an agonist can still cause a change in the receptor as though it were the normal ligand. Antagonist bind without triggering the changes that occur with the normal ligand; can inhibit the receptor by preventing the natural second messenger from activating
How do cells shut down signaling?
• Can reduce amount of free ligand, reducing total amount of signal • Can reduce the sensitivity of the receptor or the amount of receptor in the cell
How do neurons shut down signals?
They reduce the amount of neurotransmitter present at synapses via reuptake.