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211: Cell Biology > 10. GPCRs > Flashcards

10. GPCRs Flashcards

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1
Q

how many TMS alpha helices in GPCRs

A

7

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2
Q

how many extra- and intracellular domain

what is each used for?

A

4 extracellular domains
- used to interact with stimulus

4 intracellular domains
- used to interact with G-proteins

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3
Q

GPCRs have an 8th alpha helix, where is this located

A

at the c-terminal end on the cytosolic side of the plasma membrane

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4
Q

what is the 8th alpa helix (H8) covalently bound to

A

a membrane phospholipid called palmitic acid

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5
Q

name 3 functions mediated by GPCRs

A

hormone action
hormone secretion
cell growth

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6
Q

what % of medicines exert their effects by influencing G-protein pathways

A

60%

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7
Q

give 2 examples of GPCRs

A

beta-adrenergic receptor

alpha adrenergic receptor

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8
Q

what hormone do beta-adrenergic receptors respond to

A

epinephrine (fight or flight hormone)

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9
Q

describe the structure of beta-adrenergic GPCRs

A

7 alpha helices that form a barrel structure

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10
Q

where on beta-adrenergic receptors does epinephrine bind

A

in the centre of the barrel

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11
Q

what happens when epinephrine binds to beta-adrenergic GPCRs

A

interacts with 15 specific amino acids on the TMS helices

= induces a conformational change - allows the receptor to activate the G-protein

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12
Q

the G-proteins involved in the beta-adrenergic pathway are what?

A

heterotrimeric

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13
Q

what does heterotrimeric mean?

A

composed of 3 different subunits: alpha, beta and gamma

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14
Q

which subunit on a g-protein can bind GDP or GTP

A

alpha subunit

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15
Q

what is the name of the GTP/GDP binding site on g-proteins

A

guanyl nucleotide binding site

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16
Q

describe the G-protein cycle

A
  1. inactive form = GDP is bound to the guanyl binding site
  2. epinephrine binds = conformational change - activating the G-protein
  3. GDP exchanged for GTP
  4. alpha subunit bound to GTP dissociates and carries out downstream signalling
  5. to switch off signalling GTP is hydrolysed back into GDP and alpha subunit recombines
  6. cycle continues
17
Q

what does the alpha subunit-GTP complex bind to

A

adenylate cyclase

18
Q

describe the structure of adenylate cyclase

A

12 TMS alpha helices

2 domains: 6 helices in each

19
Q

each domain has a catalytic domain, what does this do?

A

converts ATP into cAMP

20
Q

what does cAMP activate

A

protein kinase A

21
Q

what does protein kinase A do?

A

increase lipid hydrolysis

decrease glycogen synthesis

22
Q

protein kinase has 4 subunits,, what does each do?

A

2 catalytic subunits

2 regulatory subunits

23
Q

what happens when cAMP binds to kinase A

A

cAMP binds to regulatory binding site causing conformational change - removes pseudo substrate from catalytic domains

= activates the protein kinase to phosphorylate downstream signalling intermediates

24
Q

what do all g-protein alpha subunits have

A

intrinsic GTPase activity

25
Q

what occurs as soon as GTP binds to guanyl nucleotide binding sites

A

hydrolysis immediately occurs by intrinsic GTPase activity

26
Q

signal termination can occur in 3 ways, what are these?

A
  1. dissociation
  2. phosphorylation by GPCR kinase
  3. endocytosis
27
Q

describe how signal termination can occur by phosphorylation by GPCR kinase

A

kinase enzymes can phosphorylate the cytosolic tail of the receptor

allows proteins called arrestin to bind, preventing the GPCR interacting with the G protein

28
Q

how do inhibitory hormones inhibit g-proteins

A

inhibits adenylate cyclase = so no cAMP is produced

  • downstream signalling is reduced
29
Q

what do alpha-adrenergic receptors do

A

lead to activation of phospholipase C by the activated G-protein

30
Q

what does phospholipase C do

A

hydrolyses PIP2 in half

this produces DAG and IP3

31
Q

where is DAG produced from cleavage

A

in the membrane

32
Q

where is IP3 produced from cleavage

A

in the cytosol

33
Q

what does DAG do

A

activates protein kinase C = phosphorylation cascade

34
Q

what does IP3 do?

A

releases calcium from intracellular stores

35
Q

what can calcium do

A

act as a second messenger

211: Cell Biology (20 decks)

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