Intracellular Signalling Pathways Flashcards
What is signal transduction?
extracellular/Intracellular receptors, ligand binding, generates response
What are the 3 receptor superfamilies?
GPCRs.
Ligand-gated ion channels.
Receptors with intrinsic enzymatic activity
Describe what a ligand is
term used for something that interacts with a receptor without knowing what it does, binding activates, directly/indirectly brings about change
What is the difference between and agonist and an antagonist?
Antagonist: bind to receptor = do not activate it (high degree of affinity but no efficacy) = blocks effects of agonist
Agonist: bind to receptor = activate it = intracellular transduction
What does GPCR stand for?
G protein-coupled receptors
What is the structure of a GPCR?
7 transmembrane regions. Linked by short sequences. N + C terminal –> variation in size of GPCR comes from size of N + C.
Binding: buries between AA side chins in middle of TM proteins, or at N terminus
List the stages of how a GPCR works
Ligand binds, changes conformation of receptor = interaction with G protein (specific), G protein activates, exchange of GDP –> GTP on Gα subunit, α and βγ subunits dissociate (type of subtype = diff signalling) –> each can interact with effector proteins (effector).
Termination: α subunit GTPase activity hydrolyses GTP –> GDP. α-GDP and βγ subunits reform to inactive complex
Where does GPCR ligand binding take place?
The cell membrane
How does cholera work?
toxin = GTPase unable to hydrolyse GTP, permanent on state = high levels cAMP
How does pertussis work?
stops GDP swapping for GTP
What is cAMP?
α-GTP (from GPCR pathway) stimulates adenylyl cyclase, ATP changes to cyclic AMP, cAMP exerts actions through cyclic AMP-dependent protein kinase (PKA): secondary messenger
What is PKAs structure?
4 subunits. 2 – R: regulate activity of C units. 2 – C: catalytic (kinase activity). Catalytic C subunits phosphorlyates target proteins in cell
Activated by the binding of 4 cAMP.
Via what method is Ca2+ increased in the cell from across the cell membrane?
LGIC: ligand gated ion channel, most activated by neurotransmitters, they bind = open, influx of Ca2+.
VOCC: voltage operated Ca2+ channel, depolarisation allows Ca2+ to flow down conc gradient.
SOC: Ca2+ sensor on ER/SR detects storage is low, gives off SER signal, SOC channel lets Ca2+ in
How is Ca2+ increased from the ER/SR?
Ryanodine receptors: Ca2+ induced Ca2+ release (CICR)
IP3R: α-GTP (from GPCR pathway) stimulates phospholipase C = cleavage of PIP2 –> IP3 (secondary messenger) + DAG, IP3 binds ER/SR receptors = Ca2+ release from storage = increase conc 5-10 fold
How is [Ca2+] lowered in the cell?
PMCA: use 1 ATP to transfer 1 Ca2+ out of cell
NXC: (Na/Ca exchanger) 3 Na+ in for 1 Ca2+ out
SERCA: use 1 ATP to transfer Ca2+ into ER/SR storage
Other than pumps, how can a Ca2+ increase be opposed?
Relative impermeability of the plasma membrane to Ca2+. Ca2+ ‘buffer’ proteins (Ca2+ -binding proteins)
What is signal amplification?
key feature of many cell signalling pathways, allow small changes in extracellular signals to elicit significant changes in cellular behaviour
Give an example of a signalling pathway in action
Inotropy (force which the heart contracts) in the heart:
nor/adrenaline binds to GPCR B1 = +cAMP = triggers VOCC to let in more Ca2+ = bigger contraction
Smooth muscle contraction:
noradrenaline binds GPCR A1 = vasoconstriction
ACh binds GCPR M3 = bronchoconstriction
Where is there high and low concs of Ca2+?
High = extracellular and ER/SR
Low = cytoplasmic
What ligands bind GPCRs?
ions, neurotransmitters, peptide/non-peptide hormones, large glycoproteins
Explain QISS QIQ
sympathetic
Q: A1, +PLC = PIP2 –> IP3 (IP3R +Ca) + DAG (PKC)
I: A2, -AC = -ATP –> -cAMP = -PKA
S: B1, +AC = +ATP –> +cAMP = +PKA (VOCC+P = Ca)
S: B2, +AC = +ATP –> +cAMP = +PKA
parasympathetic
Q: M1, +PLC = PIP2 –> IP3 (IP3R +Ca) + DAG (PKC)
I: M2, -AC = -ATP –> -cAMP = -PKA
Q: M3, +PLC = PIP2 –> IP3 (IP3R +Ca) + DAG (PKC)
Why does Ca2+ need to be tightly monitored?
high levels = toxic
How can GPCRs modulate neurotransmitter release?
GPCRs on presynaptic membrane activated e.g. morphine on opioid receptor, gamma-beta subunit inhibits VOCC = reduce influx of Ca2+ = reduce neurotransmitter release
What is the actual name of a G protein?
guanine nucleotide binding protein
Why do GPCR reactions occur on the plasma membrane?
all the substances are localised for a more efficient response
