M&R Session 6- Structure Of Receptors- Common Structural Motifs Flashcards
What is endocrine signalling?
Hormone release by a signal cell goes into the bloodstream and acts on a target cell.
What is paracrine signalling?
The release of a local chemical mediator by one cell then effects nearby cells of the same tissue.
What is synaptic signalling?
The neurotransmitter released by the presynaptic bouton travels across the synapse and acts on the post synaptic membrane receptor.
What type of signalling molecule can cross the plasma membrane and bind to intracellular receptors? Give an example.
Hydrophobic.
Steroid hormones and thyroxine
What type of signalling molecule requires a cell surface receptor?
Hydrophilic
Define receptor
A molecule that recognises specifically a second molecule (ligand) and that brings about regulation of a cellular process as a result of its binding.
When is a receptor silent?
In the unbound state
Define ligand
A molecule that specifically binds to a receptor.
When is a ligand an agonist?
When its binding brings about activation of the receptor
When is a ligand an antagonist?
When its binding doesn’t cause activation, but prevents an agonist from binding.
What is an acceptor?
A molecule often classed as a receptor.
It can however, function without the binding of a ligand.
Why is the ligand binding to receptors of higher affinity that substrate binding to enzymes?
Receptors can detect their ligand a at lower concentrations.
What is the agonist of nicotinic and muscarinic receptors respectively?
Nicotine and muscarine
What is the highest affinity antagonist of M1 receptors?
Pirenzipine
What is the antagonist of M2 receptors?
Gallamine
What is antagonist of M3 receptors?
Hexahydrosiladiphenol
What are the similarities between receptor binding sites and active sites of enzymes?
- binding at both is specific
- specificity of binding is governed by the shape of the binding site
- binding to both is often reversible
- induce a conformational change
- there is no conformational change of the ligand/ substrate
What are the differences between receptor and enzyme binding?
-affinity of ligand binding compared to substrate binding is higher.
What is auto phosphorylation?
When the binding of an agonist to the extracellular receptor site activates protein kinase and causes the receptor to phosphorylate tyrosine residues on its partner receptor.
What are the 4 signal transducers of hydrophilic signals to intracellular events?
- Membrane bound receptors with integral ion channels
- Membrane bound receptors with integral enzyme activity
- Membrane bound receptors without enzymes or ion channels (7tmdr)
- Intracellular receptors
Give an example of a membrane bound receptor with integral ion channel and explain how it works
nAChR - binds to 2 alpha subunits which causes conformational change and opening of the channel, allowing sodium and potassium ion movement.
Give an example of a membrane bound receptor with integral enzyme activity and briefly explain how it works
Tyrosine kinase-linked receptor
Binding of an agonist to extracellular site causes conformational change that activates protein kinase enzyme.
This auto-phosphorylates tyrosine residues on the receptor.
These phosphorylated tyrosine are recognised by a transduction protein or enzymes.
Explain how membrane bound receptors with no enzyme or channel activity work. - 7 transmembrane domain receptors
They are coupled to G proteins.
The binding of a receptor causes a conformational change which activates GDP/GTP exchanged in G proteins. They then transduce the message to an enzyme/channel in the membrane.
Give an example of an intracellular receptor and explain their mechanism
Steroid hormones
They are hydrophobic therefore cross the plasma membrane and bind to intracellular receptors in the cytoplasm or nucleus.
Then bind to DNA binding site and regulate gene expression
How does amplification of a signal occur?
Stimulating enzyme activity
What does noradrenaline bind to in cardiac pacemaker cells to increase heart rate?
Beta -1 adrenoceptors
What does ACh bind to in cardiac pacemaker cells to decrease heart rate?
M2 muscarinic receptors
