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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
What does alpha-GDP have a high affinity for?
Beta-gamma
26
What does alpha-GTP have a low affinity for?
Beta-gamma
27
What can alpha-subunit hydrolyse?
GTP
28
Where do the complexes of G-protein coupled receptors sit?
Inside plasma membrane
29
Describe G-protein cycle
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
What is PKA?
Protein Kinase A | Tetrameric protein with 2 types of polypeptide chain
31
Describe inactive PKA
Subunits bound together + R subunits suppresses activity of C subunit
32
What is the C + R subunit in PKA?
``` C = catalytic R = regulatory ```
33
What happens to make PKA active?
cAMP binds to dissociate | C subunit becomes active = phosphorylate other proteins
34
What does PKA do?
Catalyse transfer of ATP to specific serine/threonine residue on substrate proteins
35
What is the kidney collecting duct activated by?
Vasopressin + stimulates H2O retention
36
What is vascular smooth muscle + cardiac muscle activated by?
Adrenaline + promotes relaxation/increases HR
37
What is colonic epithelium activated by?
Various factors + promotes fluid/electrolyte secretion
38
What is the pancreas activated by?
By glucagon + promotes release of glucose in blood
39
Describe what happens in terminal signal transduction
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
What are PDE's inhibited by?
Caffeine
41
Describe desensitisation of receptor
Protein phosphorylation = cellular response PKA phosphorylates beta-ARK + increases activity beta-ARK phosphorylates beta-adrenoreceptors + reduces affinity for adrenaline = reduced cellular response
42
What are the effects of kinase opposed by?
Protein phosphatases
43
What did the 1st G-protein contain?
Alpha subunit | = activates adenylyl cyclase (AC)
44
What did alpha-s subunit of G-protein do?
Activate AC
45
What did alpha-i subunit of G-protein do?
Inhibit AC
46
What are G-proteins a target for?
Bacterial toxins
47
What does the cholera toxin do to G-proteins?
Acts on alpha-s subunit + causes ADP-ribosylation = prevents hydrolysis of GDP = persistent activation of alpha subunit + PKA
48
What does the pertussis toxin do to G-proteins?
``` 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
What do Gq proteins contain + why?
Alpha-q11 subunits | = allow hormones/neurotransmitters to activate amplifier enzyme
50
Describe Gq proteins 2nd messengers
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
What is IP3?
2nd messenger that stimulates Ca2+ release from ER
52
Describe IP3 function
Hydrophilic = enters through cytoplasm | Binds to receptors on ER = promotes release of Ca2+
53
Describe intracellular responses mediated by Ca2+
Each CaM binds to 4 Ca2+ Ca2+-CaM complex activates PDE + CaM kinases CaMKs phosphorylates serine + threonine residues on no. of substrate proteins
54
What is CaM?
Calmodulin
55
What are CaMKs involved in?
Smooth-muscle contraction
56
What do alpha1-adrenoreceptor Gq-protein coupled receptors do?
Mediates vascular smooth muscle contraction by increasing intracellular free Ca2+, activating CaMKs
57
What are the effects of DAG?
Increases activity of Ca2+-dependent protein kinases | Evokes cellular response by phosphorylating other proteins
58
What is DAG + why is it important?
Hydrophobic | = remains in membrane
59
What can PKCs do?
Potentiate effects of IP3
60
What does alpha1-adrenoreceptor do to blood pressure?
Vasoconstriction Via Gq-PLC-IP3 = increases BP
61
What does beta2-adrenoreceptors do to blood pressure?
Vasodilation Via Gs-cAMP-PKA = decreases BP
62
What are muscarinic receptors?
Gq/Gi coupled receptors
63
Describe receptor guanylyl cyclase
Contain 2 guanylyl cyclase domains = convert GTP to cGMP = activates downstream kinases
64
Describe the mechanism of signalling for receptor guanylyl cyclase
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
Describe receptor serine/threonine kinases
Contain serine-threonine kinase domains | = phosphorylate target proteins
66
Describe mechanism of signalling for receptor serine/threonine kinases
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
Describe receptor tyrosine kinases
Contain tyrosine kinase domains | = phosphorylate themselves/other proteins
68
Describe mechanism of action for receptor tyrosine kinases
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
Describe tyrosine kinase-associated receptors
DO NOT contain kinase domains | Instead associated non-covalently with cytoplasmic domains
70
Describe mechanism of action for tyrosine kinase-associated receptors
Binding of 1st messenger to receptor = conformational change = dimerization of receptor = activation of associated Tyr kinases = "phosphotryosine motifs" = recruit intracellular signalling molecules = response
71
Describe receptor tyrosine phosphatases
Contain tyrosine phosphates domains | Dephosphorylate target proteins
72
Describe mechanism of action for receptor tyrosine phosphatases
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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