Session 7.4: Intracellular signalling pathways 1

Question 1

what is the general outline of signalling pathway

Answer 1

receptor (GPCR) -> G protein -> effector

Question 2

what can effectors be

Answer 2

enzymes

ion channels

Question 3

what are some examples of enzymes that can act as effectors

Answer 3

adenylyl cylase (ATP-> cAMP)
phospholipase C (PIP2-> IP3 +DAG)
phosphoinositide 3-kinase (PIP2-> PIP3)
cGMP phosphodiesterase (cGMP -> 5'-GMP)

Question 4

what are some examples of ion channels that can act as effectors

Answer 4

voltage operated calcium channels (VOCCs)

G protein regulated inwardly-rectifying potassium channels (GIRKs)

Question 5

how is adenylyl cylase activity produced

Answer 5

GPCR activated by agonist, receptor interacts with G protein (alpha S), the G protein undergoes GDP -> GTP exchange, alpha S-GTP moves along plane of membrane and interacts with adenylyl cylase and activates it, converts ATP-> cAMP, which can then regulate cellular activity

Question 6

what proteins does adenylyl cyclase regulate

Answer 6

cyclic AMP-dependent protein kinase (PKA) - binds to this. contains two C subunits = catalytic, and two R subunits = regulatory. when cyclic AMP conc low, regulatory subunits bind to catalytic subunits to inhibit it, then when high - cAMP binds to regulatory subunits and weakens the bond between them, releasing regulatory subunits (inhibitory) to active catalytic subunits. the catalytic subunits phosphorylate target proteins in the cell (less or more active etc of protein - diff outcomes)

Question 7

what different GPCR mediate the pathway involved with adenylyl cyclase

Answer 7

interact with G protein S

• beta adrenoreceptors
• D1 dopamine receptors
• H2 histamine receptors

Question 8

how is adenylyl cyclase activity inhibited

Answer 8

different types of GPCR interact with Gi type G proteins to facilitate GDP-> GTP exchange, active alpha I component which interact with adenylyl cyclase, inhibiting it and its affect on protein kinases

Question 9

how do agonists regulate phospholipase C

Answer 9

agonist binds to GPCR, interacts with G protein that contain alpha q subunits, stimulating GDP->GTP exchange. this interacts with and activates phopholipase C, which interacts with membrane phospholipid called PIP2, causing cleavage of PIP2-> IP3 + DAG. DAG remains in membrane and IP3 moves through cytoplasm and interacts with IP3 receptors in ER, calcium moves out into cytoplasm down conc gradient (increase by 5-10 fold)
DAG interacts and binds with protein kinase C - phosphorylates substrates proteins

Question 10

what different GPCR mediate the pathway involved with phospholipase C

Answer 10

types of GPCR that interact with Gq coupled receptors:

• alpha 1- adrenoreceptors
• M1-muscaranic receptors
• H1-histamine receptors

Question 11

how is a signal amplified

Answer 11

a small change in initial stimulus - large physiologically relevant change in cell
eg: few molecules of adrenaline binding to cell surface beta-adrenoreceptors = large cellular response
the activation of adenylyl cyclase generates many molecules of cAMP which binds and activates protein kinase A, which can in turn phosphorylate lots of target proteins