Session 6 - Receptors + Membrane Turnover Flashcards
What is the affinity of a ligand to a receptor in comparison to enzymes and substrates? And why is this necessary?
Much higher
This is required because Ligands are often present in much smaller concentrations than substrates
What is an acceptor? How are receptors different?
An acceptor operates in the absence of its ligand
Receptors are silent are rest
Define a ligand
Any molecule that binds specifically to a receptor site
Differentiate agonists and antagonists?
An agonist causes activation of a receptor
An antagonist binds without causing activation
What kind of molecules require signal transduction to exert their actions?
Hydrophilic signalling molecules
What three ways can a membrane transduce a signal to the inside of the cell?
- Intergral ion channels
- Integral enzyme activity
- By coupling to effectors through transduce get proteins
Describe the classical ligand-gated ion channel and give an example
Petameric subunit structures with 4 transmembranous domains
E.g. Nicotinic Ach receptors
How does binding of a ligand to a receptor with integral enzyme activity cause a cellular response? And give an example
- binding causes a conformational change
- this change activates intrinsic enzyme activity
E.g. Tyrosine kinase linked receptors
How do tyrosine kinase receptors cause a cellular response upon activation by a ligand?
- dimers auto phosphorylate each other
- phosphorylated receptors are recognised either by transduce get proteins or directly by enzymes
- Effector enzymes become activated allosterically/ or by tyrosine phosphorylation by the receptor
Describe the structure of G-protein coupled receptors
7 transmembranous domains coupled to an effector molecule via a transducing molecule
Name some examples in the body where G-protein coupled receptors are present
Muscarinic Ach receptors, dopamine receptors, light, smell + taste receptors
What is integrated signalling?
Seperate G-protein coupled receptors act simultaneously to both inhibit and activate the effector
Name some hydrophobic Ligands
Cortisol, oestrogen, testosterone + T3+4
How do hydrophobic Ligands cause a cellular response?
- pass through plasma membrane, into the cell
- activated receptors are usually bound to chaperone proteins which dissociate upon activation
- receptors translocates into nucleus, binds to control regions, regulating gene expression
- usually slower
Name the ligand and receptors that can increase and decrease heart rate
Increase = Beta-1 adrenoreceptors - Noradrenaline
Decrease = M-2 Muscarinic receptors - Ach
Name the ligands and that can cause glycogen breakdown and synthesis in hepatocytes
Synthesis = Insulin
Breakdown = Glucagon
Describe the process of phagocytosis
- binding of specific cell surface receptors
- cell extends pseudopods that permit further receptor interactions + membrane invagination
- phagosomes fuse with lysosomes to form phagolyosomes which permits the degradation of the material
Describe the process of pinocytosis
- invagination of plasma membrane to form lipid vesicle
- this permits uptake of impermeable extracellular salutes + retrival of plasma membrane
- RME is a sub type
How does a non-functioning receptor effect effect the uptake of LDLs?
- prevents binding and hence uptake of LDL
- will occur if there is a mutation in the LDL binding site
- can cause a Hypercholesterolaemia
How can Hypercholesterolaemia still occur even if the receptor functions perfectly well?
- if the is a deletion mutation in C-terminal sequence
- prevents interaction of receptor with clathrin coat
- LDL receptors distributed over entire cell surface
- need to be concentrated to clathrin coated pits for efficient uptake
What is the fate of the receptor and ligand in LDL uptake and what’s is the function of the mechanism?
- Receptor is recycled
- Ligand is degraded
- Function is for metabolite uptake
What is the fate of the receptor and ligand in transferrin uptake and what’s is the function of the mechanism?
- Receptor is recycled
- Ligand is recycled
- Function is for iron uptake (metabolite uptake)
What is the fate of the receptor and ligand in Insulin uptake and what’s is the function of the mechanism?
- Receptor is degraded
- Ligand is degraded
- Function is to down regulate the amount of insulin receptors on the cell surface to stop over absorption of glucose
What is the fate of the receptor and ligand in IgA uptake and what’s is the function of the mechanism?
- Receptor is transported
- Ligand is transported
- Function is transfer large molecules across the cell
What is mechanism by which some enveloped viruses can take advantage of RME?
- adventitious binding to cell surface receptors allows them to be endocytosed
- once in endosome low pH allows viral membrane fusion with that of enzyme, releasing viral RNA into cell
- uses hosts machinery to form new particles
Give two examples of viruses that take advantage of RME
Cholera toxin and Diptheria toxin
Define receptor
A molecule that specifically recognises another molecule or family of molecules, and in response to binding brings about the regulation of a cellular process
