1.7 Receptors Flashcards
What are the 4 mains receptor types
-ligand gated ion channels
-G protein coupled receptors
-nuclear receptors
-kinase linked receptors
What is the receptor type that is inside the cell
Nuclear receptors
Which receptors use only direct coupling with the signalling molecule
-ligand gated ion channels
-kinase linked receptors
Which receptor can mediate long term effects
nuclear receptor
How long do ligand gated ion channels take to go into effect
milliseconds
How long do g protein coupled receptors take to go into effect
seconds
How long do nucelar receptors take to go into effect
hours
How long do kinase linked receptors take to go into effect
hours
Describe ligand-gated ion channels
Membrane bound channels that are an oligomeric assembly of protein subunits around a central pore. Ligands can bind to one or more sites on the channel to open or close the pore gate
Give examples of ligand gated ion channels
ionotropic glutamate, nicotinic cholinergic, GABA and 5-HT
Give an example of drug use with ligand gated ion channels
Barbiturates bind to GABA receptors to increasee Cl- influx, this causes IPSPs and cell excitability decreases
Describe G protein coupled receptors
They are large transmembrane alpha helix proteins that span the membrane 7 times and are attached to a G protein. They either activate or inhibit signal transduction stages
What can the effectors of GCPRs be
Either channels opening/closing or enzymes
What happens once a GPCR is bound to
There is a conformational change in the receptor which activates the G protein. The G protein then releases GDP and binds to GTP. The GTP-G protein can then split into the GTP bound a subunit and the B dimer. These can then interact with downstream effectors, using cAMP as the secondary messenger.
Give examples of some signalling molecules that bind to GPCRs
adrenaline, noradrenaline, dopamine, 5-HT, opiods and Ach
Describe kinase linked receptors
Composed of an extracellular receptor domain, a transmembrane helix region and an intracellular kinase domain (which is the effector)
What types of responses do kinase linked receptors usually mediate
Cell growth and responses to metabollic stimuli
What happens once the kinase domain in the kinase linked receptors are activated
The kinase catalyses the autophosphorylation of tyrosine residue in target proteins in the cell, then the tyrosine residues then bind to tyrosine kinase enzymes which remove a phosphate group from ATP.
Describe nuclear receptors
Receptors inside the cell (either in the nucleus or the cytoplasm) that can only mediate the effects of lipid soluble hormones
Give some examples of signalling molecules that can activate nuclear receptors
Steroid hormones, thyroid hormones and vitamin D
What happens once nuclear receptors are activated
They bind to DNA and promote or supress the transcription of certain genes
Give examples of drug use with nuclear receptors
Many agonists can bind to the receptors and increase the receptor interactions so that the effects on transcription are furthered. However, many antagonists can bind to the receptors and block the receptors from being activated by any signalling molecules, thus reducing the effects on transcription.
What shape do dosage response curves usually take on
Sigmoidal (S shaped)
Describe the 3 stages in a sigmoidal curve
lag phase- at low doses, there is little response in effect
linear phase- at intermediate doses, the response increases proportionately
plateau phase- at higher doses, the response levels off
What is EC50
The dosage needed to give half of the maximum response
What is EC50 used to measure and what would a high EC50 indicate
It is used to measure potency and a high EC50 would indicate a low potency
What is efficacy at the molecular level
The ability of a drug to produce an effect
What is efficacy at the organism level
The maximum effect of a drug (seen by how high up the y axis of the dosage response curve it goes)
