a protein that is able to interact with molecules, whereby changing a cell's physiology
Time frame: milliseconds
Examples: nicotinic, acetylcholine
Time frame: seconds
Examples: muscarinic, acetylcholine
Receptor kinase receptors
Time frame: hours
Time frame: hours
The ability of a cell to respond to a molecule is dependent upon _____?
whether the cell expresses the receptor that the molecule targets
Three characteristics of receptors
- they have finite lifespans
- they undergo processes of synthesis and degradation
- # can be affected by diseases and degree of stimulation (by exogenous or endogenous substances)
What roles do lysosomes play in receptor modification?
they are acidic organelle responsible for protein degradation in the endocytic and secretory pathways
How do proteosomes degrade proteins in a "discriminate fashion?"
they require a signal (e.g. ubiquitination) and typically target cytosolic or nuclear proteins
What is the Ubiquitous Protein System?
seeks and destroys damaged and excessive proteins by marking targets with ubiquitin/enzyme complex acting as a death signal to proteosomes
a decline in the response to repeated or sustained application of an agonist due to changes at the level of the receptor; uncoupling b/t receptor activation and downstream effect (signaling efficiency has changed)
receptors on surface are endocytosed or degraded due to repeated stimulation by an agonist; important for tolerance (e.g. opioid tolerance)
cellular response to repeated stimulation of a receptor is reduced; contributed to by both receptor downregulation and desensitization; is reversible
very acute, sudden decrease in response to receptor stimulation
Increased # of receptors -- can be due to enhanced synthesis or decreased degradation/internalization
less stimulus is needed to produce an effect -- can be due to greater signaling molecules (increased signaling efficiency)
Molecules that activate receptors; can be partial or full
What is the mechanism of action for partial agonists?
they compete for the same receptor and decrease a full agonist's activity