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Pharmacology > Extracellular Receptor Signalling Pathways > Flashcards

Extracellular Receptor Signalling Pathways Flashcards

1
Q

Describe signal transduction

A

Extracellular signal molecule activates membrane receptor
Transduced via certain pathway
Activate cellular response

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2
Q

What is the pathway for signal transduction

A 
External signal
Receptor
Transducer
Amplifier
Response
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3
Q

What are extracellular signal molecules?

A

“1st messenger”

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4
Q

What are intracellular molecules?

A

“2nd messenger”

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5
Q

What are membrane proteins?

A

Transducers

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6
Q

What do membrane proteins (transducers) do?

A

Converts messages of extracellular signals into intracellular messages

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7
Q

What are some cellular responses?

A 
Altered ion transport
Altered metabolism
Altered gene expression
Altered cell shape or movement 
Altered cell growth + division
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8
Q

What are some chemicals that serve as extracellular signalling molecules?

A

Amines
Peptides
Steroids
Other small molecules - eg. amino acids, ions + gases

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9
Q

What are the 4 main classes of receptors?

A

Ligand-gated ion channels
G-protein coupled receptors
Enzyme-linked receptors
Nuclear receptors

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10
Q

What happens when signal molecules bind to ligand-gated ion channels?

A

Conformational change = OPEN

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11
Q

What are ionotropic receptors (nicotinic acetylcholine receptors)?

A

Ligand gated ion channels that mediate effects of acetylcholine on muscle

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12
Q

What happens when acetylcholine binds to ionotropic receptors?

A

Na+ enters
Binds to nicotine
Electrical event (inward Na+ current) = triggers response
Ca2+ may enter

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13
Q

What is GABA A selective for?

A

Cl-

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14
Q

What is GABA A activated by?

A

y-amino butyric acid - CNS neurotransmitter

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15
Q

What type of receptors GABA A?

A

Inhibitory receptor

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16
Q

What are metabotropic receptors linked with?

A

Ion channel on plasma membrane

Through signal transduction pathway

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17
Q

What are metabotropic receptors more sensitive to?

A

Muscarine than nicotine

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18
Q

What is an example of a metabotropic receptor?

A

GABA B

= activates K+ channels

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19
Q

What are examples of ionotropic?

A

Nicotinic

GABA A

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20
Q

What are examples of metabotropic?

A

Muscarinic

GABA B

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21
Q

Describe G-protein receptors

A

All have 7 transmembrane domains
Activated by many molecules
Play role in regulation of cell function

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22
Q

What do G-coupled receptors consist of?

A 
3 polypeptide chains
Alpha, beta + gamma
16 alpha subunits
5 beta
11 gamma
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23
Q

What do beta + gamma subunits do in G-protein coupled receptors?

A

Bind tightly to each other

= beta-gamma subunit

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24
Q

What does alpha subunit bind to in G-protein coupled receptors?

A

Has guanine nucleotide binding site

= binds to GTP or GDP

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25
Q

What does alpha-GDP have a high affinity for?

A

Beta-gamma

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26
Q

What does alpha-GTP have a low affinity for?

A

Beta-gamma

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27
Q

What can alpha-subunit hydrolyse?

A

GTP

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28
Q

Where do the complexes of G-protein coupled receptors sit?

A

Inside plasma membrane

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29
Q

Describe G-protein cycle

A

Unstimulated cell
Adrenaline binding to beta-adrenoreceptor
Allows beta-adrenoreceptor/G-protein interaction
Allows GDP/GTP exchange
Allows alpha-subunit liberation
Free alpha subunit activates AC
Unbinding of adrenaline/GTP hydrolysis

30
Q

What is PKA?

A

Protein Kinase A

Tetrameric protein with 2 types of polypeptide chain

31
Q

Describe inactive PKA

A

Subunits bound together + R subunits suppresses activity of C subunit

32
Q

What is the C + R subunit in PKA?

A 
C = catalytic
R = regulatory
33
Q

What happens to make PKA active?

A

cAMP binds to dissociate

C subunit becomes active = phosphorylate other proteins

34
Q

What does PKA do?

A

Catalyse transfer of ATP to specific serine/threonine residue on substrate proteins

35
Q

What is the kidney collecting duct activated by?

A

Vasopressin + stimulates H2O retention

36
Q

What is vascular smooth muscle + cardiac muscle activated by?

A

Adrenaline + promotes relaxation/increases HR

37
Q

What is colonic epithelium activated by?

A

Various factors + promotes fluid/electrolyte secretion

38
Q

What is the pancreas activated by?

A

By glucagon + promotes release of glucose in blood

39
Q

Describe what happens in terminal signal transduction

A

cAMP hydrolysed by phosphodiesterase (PDE)
Hormone removed = PDE rapidly clears cAMP from cell
Unbinding of cAMP from R subunit
= increases affinity for C subunit
Protein reassembles into tetramer + inactivated

40
Q

What are PDE’s inhibited by?

A

Caffeine

41
Q

Describe desensitisation of receptor

A

Protein phosphorylation = cellular response
PKA phosphorylates beta-ARK + increases activity
beta-ARK phosphorylates beta-adrenoreceptors + reduces affinity for adrenaline
= reduced cellular response

42
Q

What are the effects of kinase opposed by?

A

Protein phosphatases

43
Q

What did the 1st G-protein contain?

A

Alpha subunit

= activates adenylyl cyclase (AC)

44
Q

What did alpha-s subunit of G-protein do?

A

Activate AC

45
Q

What did alpha-i subunit of G-protein do?

A

Inhibit AC

46
Q

What are G-proteins a target for?

A

Bacterial toxins

47
Q

What does the cholera toxin do to G-proteins?

A

Acts on alpha-s subunit + causes ADP-ribosylation
= prevents hydrolysis of GDP
= persistent activation of alpha subunit + PKA

48
Q

What does the pertussis toxin do to G-proteins?

A 
Act on alpha-i subunit
= locks subunit into inactive configuration
= prevention activation of receptors
= prevents inhibitor control over AC/PKA
= increased levels of cAMP + PKA
49
Q

What do Gq proteins contain + why?

A

Alpha-q11 subunits

= allow hormones/neurotransmitters to activate amplifier enzyme

50
Q

Describe Gq proteins 2nd messengers

A

Stimulate phospholipase C (PLC)
PLC cleaves PIP2 into inositol, 1,4,5-triphosphate (IP3) + diacylglycerol (DAG)
IP3 H2O soluble
= travels through cytosol to simulate Ca2+ release
DAG remains in membrane where it recruits protein kinase

51
Q

What is IP3?

A

2nd messenger that stimulates Ca2+ release from ER

52
Q

Describe IP3 function

A

Hydrophilic = enters through cytoplasm

Binds to receptors on ER = promotes release of Ca2+

53
Q

Describe intracellular responses mediated by Ca2+

A

Each CaM binds to 4 Ca2+
Ca2+-CaM complex activates PDE + CaM kinases
CaMKs phosphorylates serine + threonine residues on no. of substrate proteins

54
Q

What is CaM?

A

Calmodulin

55
Q

What are CaMKs involved in?

A

Smooth-muscle contraction

56
Q

What do alpha1-adrenoreceptor Gq-protein coupled receptors do?

A

Mediates vascular smooth muscle contraction by increasing intracellular free Ca2+, activating CaMKs

57
Q

What are the effects of DAG?

A

Increases activity of Ca2+-dependent protein kinases

Evokes cellular response by phosphorylating other proteins

58
Q

What is DAG + why is it important?

A

Hydrophobic

= remains in membrane

59
Q

What can PKCs do?

A

Potentiate effects of IP3

60
Q

What does alpha1-adrenoreceptor do to blood pressure?

A

Vasoconstriction
Via Gq-PLC-IP3
= increases BP

61
Q

What does beta2-adrenoreceptors do to blood pressure?

A

Vasodilation
Via Gs-cAMP-PKA
= decreases BP

62
Q

What are muscarinic receptors?

A

Gq/Gi coupled receptors

63
Q

Describe receptor guanylyl cyclase

A

Contain 2 guanylyl cyclase domains
= convert GTP to cGMP
= activates downstream kinases

64
Q

Describe the mechanism of signalling for receptor guanylyl cyclase

A

Binding of ANP induces conformational change in receptor = dimerization + activation
Guanylyl cyclase activity generates cGMP
Increased conc of cGMP = activates other signalling molecules
= determines response

65
Q

Describe receptor serine/threonine kinases

A

Contain serine-threonine kinase domains

= phosphorylate target proteins

66
Q

Describe mechanism of signalling for receptor serine/threonine kinases

A

1st messenger binds to receptor Type II
Receptor Type I binds forming ternary complex with Type II + 1st messenger
Type II receptor phosphorylates Type I = activating Ser-Thr kinase activity of Type I
Type I phosphorylates target protein

67
Q

Describe receptor tyrosine kinases

A

Contain tyrosine kinase domains

= phosphorylate themselves/other proteins

68
Q

Describe mechanism of action for receptor tyrosine kinases

A

Binding of 2 molecules of insulin = receptors dimerise
Use their cytoplasmic Tyr kinase activity to phosphorylate each other at multiple tyrosine residues
= “phosphotryosine motifs”
Recruit intracellular signalling molecules = response

69
Q

Describe tyrosine kinase-associated receptors

A

DO NOT contain kinase domains

Instead associated non-covalently with cytoplasmic domains

70
Q

Describe mechanism of action for tyrosine kinase-associated receptors

A

Binding of 1st messenger to receptor = conformational change = dimerization of receptor
= activation of associated Tyr kinases
= “phosphotryosine motifs”
= recruit intracellular signalling molecules = response

71
Q

Describe receptor tyrosine phosphatases

A

Contain tyrosine phosphates domains

Dephosphorylate target proteins

72
Q

Describe mechanism of action for receptor tyrosine phosphatases

A

CD45 binding to receptor = conformational change = activates Tyr phosphatases
= target proteins dephosphorylated
= regulation of downstream cell-signalling events

Pharmacology (40 decks)

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