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PHA112 > Receptor & G Proteins > Flashcards

Receptor & G Proteins Flashcards

1
Q

define a superfamily?

A

group of receptors having similar bass structures and mechanism of signal transduction

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2
Q

what are the 4 superfamilies?

A
  • G protein-coupled receptors (GPCRs)
  • ligand gates ion channels (LGICs)
  • tyrosine kinase-linked receptors
  • steroid receptors (nuclear receptors)
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3
Q

what are the largest family of cell surface receptors?

A

GPCRs

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4
Q

what do GPCRs mediate?

A

cellular responses to big diversity of signalling molecules

inc:
- hormones
- proteins
- neurotransmitters

same ligand can activate many diff fam members to produce effect

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5
Q

what is the location and signal transduction mechanism of the M1 receptor?

A

nerves

inc IP3, DAG cascade

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6
Q

what is the location and signal transduction mechanism of the M2 receptor?

A

heart, nerves

dec cAMP prod, activation K+ channels, inhibition Ca2+ channels

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7
Q

what is the location and signal transduction mechanism of the M3 receptor?

A

glands, smooth muscle, endothelium

inc IP3, DAG cascade

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8
Q

what is the location and signal transduction mechanism of the M4 receptor?

A

CNS

dec cAMP prod, activation K+ channels

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9
Q

what is the location and signal transduction mechanism of the M5 receptor?

A

CNS

inc IP3, DAG cascade

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10
Q

where are muscarinic receptors located?

A

peripheral tissues and CNS

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11
Q

what are the 5 subtypes of muscarinic receptors?

A

M1, M2, M3, M4, M5

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12
Q

what are M1, M3 and M5 coupled to?

A

Gq

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13
Q

what are M2 and M4 coupled to?

A

Gi

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14
Q

what do Gq coupled receptors hydrolyse?

A

PIP2

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15
Q

what do Gi coupled receptors negatively regulate?

A

adenylyl cyclase + decrease cAMP production

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16
Q

where are M1, M3 and M4 located and what do they mediate?

A

cerebral cortex + hippocampus

mediate effects of ACh on learning + memory

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17
Q

what do M1 and M4 occur in and what can they also mediate?

A

striatum

cholinergic signalling in extrapyramidal motor circuits

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18
Q

where is M2 concentrated in and what does it act as?

A

basal forebrain

autoreceptors to control ACh synthesis + release

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19
Q

what is the location, structure and signal transduction mechanism of the Nm receptor?

A

skeletal neuromuscular junction

pentameric (2-alpha-beta-delta-gamma)

Na+ depolarising ion channel

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20
Q

what is the location, structure and signal transduction mechanism of the Nn receptor?

A

post-synaptic cell bodies, dendrites

alpha + beta subunits only usually as 2-alpha-3beta

Na+ depolarising ion channel

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21
Q

where are nicotinic receptors located?

A

NMJ , autonomic ganglia, CNS

22
Q

what superfamily are the nicotinic receptors part of?

A

LGIC

23
Q

what does the activation of nicotinic receptors lead to?

A

influx of Na+ ions

24
Q

how many subunits are nicotinic receptors composed of?

A

5

25
Q

where are the alpha1 and beta1 subunits located?

A

muscle

26
Q

what stoichiometry ratio are neuronal nACHR’s composed of (alpha to beta)?

A

2:3

27
Q

what can homomeric receptors (alpha7) form?

A

a channel

28
Q

alpha-adrenoreceptors

alpha1 (alpha1A, alpha1B, alpha1D)

A

potency order: NA > Ad

location: post-junctional effector organs
function: smooth muscle contraction
transduction: inc IP3, DAG
agonist: phenylephrine
antagonist: prazosin

29
Q

alpha-adrenoreceptors

alpha2 (alpha2A, alpha2B, alpha2C)

A

potency order: Ad > NA

location: pre-synaptic nerve endings, post synaptic brain, blood vessels
function: inhibition transmitter release, dec sympathetic outflow
transduction: dec cAMP (Ca2+)
agonist: clonidine
antagonist: yohimbine

30
Q

beta-adrenoreceptors

beta1

A

potency order: Iso > NA > Ad

location: heart, adipose tissue, JG cell kidney
transduction: inc cAMP
agonist: dobutamine
antagonist: atenolol

31
Q

beta-adrenoreceptors

beta2

A

potency order: Iso > Ad > NA

location: bronchi, blood vessels, uterus
transduction: inc cAMP
agonist: salbutamol
antagonist: ICI118551

32
Q

dopamine receptors

D1 - 1 and 5

A

signal transduction: inc cAMP

effect: post-synaptic inhibition

33
Q

dopamin receptors

D2 - 2,3,4,

A

signal transduction: dec cAMP

effect: pre + post synaptic inhibition, stimulation/inhibition of hormone release

34
Q

where do GPCRs occur, how do they respond and what does their single polypeptide chain have?

A

cell membrane

respond in seconds

7-transmembrane helices

35
Q

what does the tail GPCRs consist of?

A

serine + threonine residues that = phosphorylated

36
Q

what does the intracellular loop occur between?

A

V and VI transmembrane domains

37
Q

what are the heterotrimeric GTP-binding proteins (G proteins) composed of?

A

alpha, beta and gamma polypeptide chains

38
Q

what do both the alpha and gamma subunits have?

A

lipid molecules that help bind them to plasma membrane

39
Q

the alpha subunit has … bound

A

GDP

40
Q

heterotrimeric GTP binding proteins are ….. and they function as … that can flip between 2 states

A

GTPases

molecular switches

41
Q

what are the 2 states?

A

active when GTP bound

inactive when GDP bound

42
Q

describe the on and off switching?

A
  • extracellular ligand binds to G protein linked receptor
  • receptor changes conformation
  • —> rel of GDP + replacement with GTP
  • switch turned off when G protein hydrolyses own bound GTP
  • converting it back to GDP
43
Q

the GTP binding causes a conformational change in the surface of alpha subunit

what does this cause the release of?

A

beta-gamma dimer

allows alpha subunit to interact with target proteins

alpha subunit = GTPase + hydrolyses GTP to GDP

then reassociates with beta-gamma complex

44
Q

GTPase activity of the alpha subunit is greatly enhanced by binding of second protein called a …

A

regulator of g-protein signalling (RGS)

45
Q

what do RGS proteins act as?

A

alpha subunit specific GTPase activating proteins (GAPs)

play imp role in shutting off g-protein mediated response

46
Q

Gs protein

A

alphaS

activates AC (inc cAMP) 
activates Ca2+ channels
47
Q

Gi protein

A

alphaI

inhibits AC (dec cAMP)
activates K+ channels
48
Q

Gq protein

A

alphaQ

activates PLC-beta turnover (inc Ca2+)

49
Q

Go protein

A

alphaO

activates K+ channels
inactivates Ca2+ channels

50
Q

Gt protein

A

alphaT

activates cGMP phosphodiesterase in rod photoreceptors

51
Q

Golf protein

A

alphaOLF

activates AC in olfactory system

52
Q

what are the 2 major pathways by which GPCRs generate small intracellular mediators?

A
  • binding of extracellular ligand -> alters conformation of cytoplasmic domain of receptor
  • cAMP pathway -> enzyme directly produces cAMP
  • enzyme produces inositol triphosphate that rel Ca2+ from ER

PHA112 (37 decks)

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