CellSig6 - 20 Flashcards Preview

Y2S2 - Cell Signalling > CellSig6 - 20 > Flashcards

Flashcards in CellSig6 - 20 Deck (20):
1

Outline three forms of desensitisation

Receptor inactivation, sequestration, down-regulation

2

What causes desensitisation?

Prolonged exposure to high concentrations of signal, adaptive/protective response, reversible process

3

What is the role of cAMP?

Small intracellular mediator

4

What is the normal IC [cAMP]?

10-7M

5

What [cAMP] can be reached when EC signal attaches?

Increases by >20 fold

6

How is cAMP synthesised?

From ATP by PM bound adenylyl cyclase

7

What is cAMP continually degraded by?

cAMP phosphodiesterase

8

How does cAMP phosphodiesterase function?

Hydrolyses cAMP to 5'AMP

9

Outline the regulation of adenylyl cyclase

Gs activates, Gi inhibits

10

How does cholera toxin affect cAMP function?

Transfers ADP ribose from NAD+ to Gs-a, inhibiting GTP hydrolysis, and causes continuous cAMP production

11

How does pertussis toxin affect cAMP function?

Transfers ADP ribose from NAD+ to Gi-a, preventing receptor interaction, and halts all cAMP production

12

How does PKA work?

4 subunits, 2 to bind with cAMP, two catalytic; cAMP binds, catalytic subunits activate

13

What is PKA's role in gene transcription?

Activates CREB in nucleus, whichis phosphrylated and binds CREB-binding protein (CBP), leading to activated target gene transcription

14

How can G-proteins directly regulate ion channels?

Direct binding of b-g to ion channels such as muscarinic acetylcholine receptors

15

How can G-proteins indirectly regulate ion channels?

Phosphrylation of ion channels by G-protein regulated kinases such as PKA/PKC; OR cyclic-nucleotide gating of ion channels

16

What is Golf involved in?

Olfactory sensation

17

How is Golf involved in olfactory sensation?

Activated by GPCR, activates adenylyl cyclase, cAMP produced opens Na channels, allowing depolarisation of neuron

18

Outline G-protein involvement in response to light

1 photon + 11-cis trans > all-trans > activates rhodopsin (GPCR) > G-transducin (Gt) release > closing of cGMP-gated Na channels

19

Outline amplification of the G-transducin pathway

1 photon > 1 rhodopsin > 500 Gt > 500 cGMP activation > 10^5 cGMP hydrolysed > 250 channels close > 10^7 cations prevented from entry > membrane-pot altered by 1mV

20

How is rhodopsin desensitised?

Phosphorylated by GPCR kinase (GRK), then bound by arrestin, uncoupling it