ICPP - Intracellular Signalling Pathways Flashcards
Why are many receptors located at the cell membrane rather than within the cell?
The majority of extracellular signalling molecules do not easily cross the cell membrane due to being hydrophilic.
What is signal transduction?
Any process by which a biological cell converts one kind of signal or stimulus into another.
What happens when a ligand binds to a receptor?
It brings about a change in cellular activity (directly or indirectly).
True or false - receptor sub-types are not general and work for many different types of ligand?
False - they are specific for one (or a limited number of) ligands.
What do agonists do?
Bind to the receptor and activate it (leading to intracellular signal transduction events).
What do antagonists do?
Bind to the receptor but do not activate it, blocking the effects of agonists at the receptor.
What do sensory GPCRs sense?
Light, odours and tastes
Which of these can GPCRs not respond to?
Ions, neurotransmitters, peptide and non-peptide hormones, large glycoproteins.
Trick question, all of them.
What is the basic structure of a GCPR?
Single polypeptide chain, 7 transmembrane spanning regions, extracellular N-terminal, intracellular C-terminal.
Which two regions of GPCRs can be responsible for ligand binding?
2-3 of the transmembrane domains, or the N-terminal region
Why are GPCRs also known as 7TM receptors?
They pass through the membrane seven times.
How do GPCRs respond to ligand binding?
They change the conformation of the protein structure.
What happens to the G protein when the GPCR changes conformation?
The GDP which is attached to it is swapped for GTP, causing it to split into an alpha and beta-gamma subunit.
Why are G proteins described as “structurally trimeric but functionally dimeric”?
They are made up of three subunits but they only split into two.
What do the alpha-GTP and beta-gamma subunits do once a G protein has split up?
They interact with effector proteins (second messenger-generating enzymes, ion channels)
How is G protein signalling terminated?
GTPase hydrolyses the GTP on the alpha subunit, turning it back to GDP. The subunits reform the inactive heterotrimeric complex.
The human genome encodes 20 G alpha, 5 G beta and 12+ G gamma proteins. How many possible combinations are there?
Over 1000
True or false - the alpha subunit is the primary determinant of which G protein the GCPR interacts with.
True
Adrenaline/noradrenaline can bind to beta-adrenoceptors, alpha 1 and alpha 2 adrenoceptors, all using the alpha subunit. What are the respective effectors?
Adenylyl cyclase (increase), adenylyl cyclase (decrease), phospholipase C (increase)
Acetylcholine can decrease adenylyl cyclase and increase phospholipase C using the alpha subunit. Which GCPR does it respectively bind to?
M2/M4 muscarinic receptor, M1/M3 muscarinic receptor.
What is the common name of the illness caused by the pertussis toxin?
Whooping cough
Which stage of the G protein function cycle does the pertussis toxin interfere with?
It prevents the GDP on the alpha unit from being swapped for GTP, meaning the subunits never separate.
Which stage of the G protein function cycle does the cholera toxin interfere with?
It prevents the GTP on the separated alpha subunit from being hydrolysed, so the subunits never rejoin and the CTFR proteins remain stuck open.
