Receptors Flashcards
What properties are receptors defined by?
recognition and transduction
Recognition:
Receptors bind reversibly with high affinity
Transduction:
Structure-dependent conversion of binding into a cellular response –> activity of efficacy
Are receptors the same as enzymes?
No
How are receptors and enzymes different?
Ligands are not changed during binding to the receptor
What is required for receptor binding interaction
Specificity
Saturability
Reversability
Specificity:
Ligand is structurally complementary to receptor, specific and high affinity interaction
Saturability:
A finite number of receptors per cell are present
Reversibility
After binding, the ligand must dissociate in an unchanged form
Low affinity –> Kd
Low
High affinity –> Kd
High
What is a saturation isotherm
The concentration of bound ligand plotted against the concentration of free ligand
The concentration of free ligands when 50% binding sites are used = Kd
Ligands that bind to a receptor at the same site have what kind of inhibition
Competitive
What is the effect of a competitive inhibitor
Decreases the apparent affinity of ligand, no effect on maximum binding at saturation
What is the classical receptor theory
Response directly related to receptor occupation
What is the modified classical theory?
The response can occur at lower concentrations of ligands than expected
Amplification of the signal can lead to spare receptors
What is an agonist
A ligand that binds to a receptor and produces a response
What is a partial agonist
A ligand that binds to a receptor and produces less than the maximum response
How is efficacy measured
The response - conversion to activated state
How is potency measured
The binding of the ligand and receptor
What are competitive antagonist
Ligands that bind to the receptor at the same site as the agonist but do not result in activation
What are noncompetitive antagonist
Ligands that bind to the receptor at a different site than the agonists and prevent activation
Which is more common - competitive or noncompetitive antagonist
Competitive
What do competitive antagonists do to efficacy and potency
Potency is decreased, efficacy is unchanged
What do noncompetitive antagonists do to efficacy and potency
Decreases max response without affecting potency
How do receptors desensitize themselves
Slow conformational change
Phosphorylation to inactive state
Binding to an inhibitory protein
What are the ways receptors respond to excess varying amounts of ligands
Desensitization
Downregulation
Upregulation
How does downregulation work
Endocytosis used for temporary sequestration or degradation of receptor
When does upregulation occur
When there is prolonged exposure to antagonists
How does upregulation work
Cells increase the number of receptors they express
