Flashcards in Intracellular Signalling Deck (24):
Describe paracrine signalling
Local, uses chemical mediators
Describe endocrine signalling
Utilises the blood stream, uses hormones
Describe synaptic signalling
Uses neurotransmitters, between a neuron and either another neuron or effector tissue
Describe a receptor
A molecule which specifically recognises a ligand or family of, and in response to this binding brings regulation of a cellular process.
In its unbound state, receptors are functionally silent.
Describe a ligand.
Any molecule that binds specifically to a receptor site.
What is the difference between an agonist and antagonist?
An agonist activates a receptor
An antagonist binds without causing a response.
Describe the difference between the affinity of a ligand at receptor sites, and the affinity of a substrate to an enzyme site.
The affinity of a ligand is generally much higher.
How are receptors classified?
Primarily by specific signalling molecules, then sub-classified by their affinity for a specific series of antagonists.
What are the four methods of signal transduction?
Receptor with integral ion channel
Receptor with integral enzyme
Receptor coupled to effectors through transducing enzymes
Intracellular receptor with DNA binding site
Decribe the difference between a receptor and acceptor
Receptors are silent at rest and stimulate biological responses with ligand binding.
Acceptors operate in the absence of a ligand, binding alone has no response.
Describe the methotrexate receptor
Modulated by methotrexate.
Is the enzyme dihydrofolate reductase.
Is an acceptor
Describe the nicotinic acetylcholine receptor
Causes depolarisation on ligand binding
Is an integral ion channel
Permeable to sodium, potassium and calcium.
Pentameric with two alpha subunits that ACh binds to.
The change in conformation on binding increases the negative charge in the channel, allowing selectivity for ions.
Multiple transmembrane domains.
Describe the GABA recepor
Integral ion channel
Amino acid gated
Permeable to chloride ions
Describe the implication of glutamate receptors in brain damage.
Integral ion channel
Glutamate is released in the brain when it is damaged, causing calcium influx into the cells which is toxic.
Describe the ATP-sensitive potassium channel.
A non-classical integral ion channel
Closes on intracellular ligand binding
Found in beta cells of the pancreas.
Describe a ryanodine receptor
Is actually an acceptor.
Causes muscle block and activation by increasing calcium release from the ER.
Calcium is also a ligand.
Describe the general structure of a receptor with integral enzyme activity.
One transmembrane domain with a binding domain extracellularly and a catalytic domain intracellularly.
Have a partner subunit.
Describe growth factor receptors
Linked to tyrosine kinase which allows autophosphorylation
Then an enzyme can bind and take the receptor into the cell, or it binds to a transducer protein which then phosphorylates the start point for an enzyme cascade.
Describe the insulin receptor.
Two alpha subunits extracellularly at the N-terminus which contains the insulin binding domain. This is attached to a beta subunit, which is bonded to the transmembrane domain.
The tyrosine kinase domain within the cell is near the C terminus.
What does G-protein stand for?
GTP-binding regulatory protein
Describe the use of GPCR in the heart (briefly) by the sympathetic and autonomic nervous systems.
Sympathetic - adrenaline or noradrenaline binds to beta-adrenoceptors. Gs activates adenylyl cyclase which increases cAMP production.
Parasympathetic - ACh binding to M2 uses Gi to inhibit adenylyl cyclase, decreasing cAMP production. The beta-gamma subunit stimulates potassium channel opening.
Where is the binding domain in a GPCR?
In the bilayer as a cleft formed by the transmembrane domain
What terminus is the G-protein coupling domain nearest?