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Semester 2 > M&R Session 7 > Flashcards

M&R Session 7 Flashcards

0
Q

By what two mechanisms can cell surface receptors act?

A

Directly alter cellular activity

Transduction of initial binding event via other intracellular components

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1
Q

What tends to happens to cells if they do not receive extracellular signals?

A

They die

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2
Q

What cellular activity can be controlled by transduction of initial binding event?

A

Contraction
Secretion
Proliferation
Differentiation

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3
Q

What are the three superfamilies of cell-surface receptors?

A

Ligand-gated (receptor operated) ion channels
Receptors w/intrinsic enzymatic activity
GPCRs

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4
Q

Which superfamily of cell-surface receptors is heterogenous?

A

Receptors w/ intrinsic enzyme activity

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5
Q

Describe the mechanism of receptors w/intrinsic enzyme activity.

A

Ligand binding activates an enzyme

Enzyme phosphorylates the receptor itself and other substrates

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6
Q

Which superfamily of cell-surface receptors do insulin receptors belong?

A

Receptors w/intrinsic enzyme activity

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7
Q

How do GPCRs have specificity of action?

A

Each receptor subtype is specific for one/ limited number of endogenous ligands

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8
Q

What is an agonist?

A

A molecule that binds to a GPCR and activates it causing intracellular signal transduction events

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9
Q

What drugs are used to treat asthma?

A

Beta-2 adrenoreceptor agonists

E.g. Salbutamol, Salmeterol

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10
Q

What type of molecules are used for analgesia/anaesthesia?

A

Mu-opioid receptor agonists

E.g. Morphine, Fentanyl

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11
Q

What are antagonists?

A

Molecules that bind to a receptor but do not activate it; they block the effects of agonists

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12
Q

What type of molecules are used to treat hypertension?

A

Beta-adrenoreceptor antagonists

E.g. Propanolol, Atenolol

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13
Q

What are Haloperidol and Sulpiride examples of?

A

Anti-schizophrenic D2 dopamine receptor antagonists

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14
Q

What effect do antagonists have on certain mechanisms?

A

Damp-down hyper activation

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15
Q

Give the key features of GPCR structure.

A 
300-1200 a.a. chain
7TMD
2 regions for ligand binding: in TMD or N-terminal region
Extracellular N-terminal
Intracellular C-terminal
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16
Q

What can drugs targeting GPCRs be used to treat?

A 
Parkinson's disease
Congestive heart failure
Thrombosis
Benign prostatic hyperplasia
Acid reflux
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17
Q

What two types of mutation can occur to cause a disease associated w/signal transduction?

A

Loss of function

Gain of function

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18
Q

What causes retinitis pigmentosa?

A

Loss of function rhodopsin mutation

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19
Q

What causes nephrogenic diabetes insipidus?

A

Love of function mutation of V2 vasopressin receptor

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20
Q

What happens in a gain of function mutation?

A

Receptor becomes independent of ligand –> endocrine changes

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21
Q

What causes familial male precocious puberty?

A

LH receptor mutation

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22
Q

What stimuli can GPCRs respond to?

A 
Light, odour, taste
Ions
Neurotransmitters
Hormones
Large glycoproteins
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23
Q

How do GPCRs cause a change in cellular activity?

A

Ligand binds –> conformational change –> GPCR activated –> interacts w/guanine-nucleotide binding protein –> activates G-protein –> GDP replaced by GTP on alpha-subunit

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24
What is the structure of a guanine-nucleotide binding protein?
Heterotrimeric | Alpha, beta and gamma subunits
25
Why is a G-protein functionally dimeric?
Once the beta and game subunits are synthesised they stick together
26
What is the function of the alpha subunit of a G-protein?
Bind to guanine nucleotide | GTPase activity
27
When does GTP have a natural tendency to bind to the alpha subunit?
When the binding site is empty
28
How do you activate a G-protein?
Guanine nucleotide exchange by replacing GDP w/GTP
29
How do you turn off a G-protein?
Hydrolyse GTP
30
Which subunits can interact w/effector proteins?
Alpha | Beta-gamma
31
What effector proteins can the G-protein subunits interact with?
2nd messenger generating enzymes | Ion channels
32
What is amplification governed by?
Timer function of the G-protein unit
33
What is timer function?
Capacity of how long the signal can be passed on for by a GPCR
34
Why can efficiency of signal transmission be targeted therapeutically?
In different pathways it can be altered
35
What is the primary determinant of receptor G-protein selection?
The ~20 different G-alpha proteins in the human genome
36
Does a GPCR have its own unique G-protein combination?
No
37
How many possible G-alpha-beta-gamma protein combinations are possible in the human genome?
>1000
38
How is a specific cellular response brought about by a GPCR?
An extracellular signal working via a specific GPCR will activate a single/small sub-population of G-proteins and effectors in the cell
39
What is the ligand, G-protein and effector for beta-adrenoreceptors?
Adrenaline/NA Gs-alpha + adenylyl cyclase
40
What is the ligand, G-protein and effector for alpha-2-adrenoreceptors?
Adrenaline/NA Gi-alpha - adenylyl cyclase
41
What GPCR, ligand and effector are used for Gq-alpha proteins?
Alpha-1-adrenoreceptors Adrenaline/NA + phospholipase C
42
What ligand, GPCR and G protein are used to stimulate cyclic GMP phosphodiester Awe?
Light Rhodopsin Gt-alpha
43
What ligand acts at M2/4 muscarinic GPCRs?
ACh
44
What G-proteins are used for M2/4 muscarinic receptors?
Gi-alpha
45
What effector does Gi-alpha activation act on?
-adenylyl cyclase
46
What ligand, G-protein and effector do M1/3 GPCRs use?
ACh Gq-alpha + phospholipase C
47
Which pathway do even numbered muscarinic receptors follow the same as?
Alpha-2-adrenoreceptors
48
Which pathway do odd numbered muscarinic receptors follow the same as?
Alpha-1-adrenoreceptors
49
Name two ADP-ribosylate specific G-proteins.
Cholera toxin | Pertussis toxin
50
What mechanism of action does cholera toxin use?
Eliminates GTPase activity of Gs-alpha | Irreversibly activates Gs-alpha
51
How does cholera toxin irreversibly activate Gs-alpha?
ADP-ribosylation of the unit prevents deactivation of Gs protein mediated signalling
52
Cells in which area of the body are infected by cholera toxin?
Small intestine
53
What happens to the toxin complex in both cholera and pertussis toxin action?
It binds to the cell and the emzyme is 'injected' into the cell
54
What type of cell does Bordetella pertussis bacteria colonise?
Tracheal epithelial
55
What characteristic symptom does pertussis toxin cause?
Whooping cough
56
By what method of action does pertussin toxin cause whooping cough?
Interferes w/ GDP-GTP exchange so Gi-alpha is irreversibly inactivated
57
How does pertussis toxin cause irreversible inactivation of Gi-alpha?
ADP-ribosylation of the subunit prevents Gi protein activation by GPCRs
58
What is PIP3?
A more phosphorylated form of the membrane phospholipid PIP2 that regulates a variety of processes - often survival signals
59
How is adenylyl cyclase regulated by agonist stimulation?
Ligand on receptor activates G-protein --> guanine nucleotide transfer --> activated Gs-alpha --> stimulates adenylyl cyclase --> secondary messenger cAMP formed
60
Which receptors are Gs coupled receptors?
Beta-adrenoreceptors D1 dopamine receptors H2 histamine receptors
61
Which receptors are Gi coupled receptors?
Alpha 2-adrenoreceptors D2 dopamine receptors My-opioid receptors
62
What does cAMP act on?
cAMP-dependent protein kinase A (PKA) Epacs (GEFs) Cyclic-nucleotide-gated ion channels (CNGs)
63
Describe the structure of PKA.
2 regulatory subunits sat in active site of 2 catalytic subunits
64
How does cAMP activate PKA?
Binds to regulatory subunits --> catalytic subunits dissociate exposing active site --> catalytic subunits phosphorylate specific target proteins in the cell that have serine or threonine residues
65
How is phospholipase C regulated by agonist stimulation?
Ligand on receptor activates G-protein --> guanine nucleotide transfer --> activated Gq-alpha --> stimulates PLC --> PIP2 into IP3 and DAG
66
Which part of the PIP2 molecule forms IP3?
Polar head group
67
Which part of the PIP2 molecule forms DAG?
Lipid moiety
68
What intracellular affect does IP3 have?
It releases calcium ions
69
What affect does DAG have?
Acts on PKC which can act on lots of different molecules to affect activity
70
Which receptors are Gq coupled receptors?
Alpha 1-adrenoreceptors M1 muscarinic receptors H1 histamine receptors
71
What is the advantage of signal amplification?
Modest concentration changes cause significant effects within cell
72
What affect does a few hundred molecules of adrenaline binding to cell surface beta-adrenoceptors have?
Glycogenolysis in the liver causing milimolar changes in blood glucose concentration
73
What magnitude of amplification does adenylyl cyclase itself cause?
Little
74
What follows activation of adenyly cyclase?
Lots of cAMP molecules released which activate PKA
75
Which two molecules cause ventricular mass to contract more forcefully?
Blood-borne adrenaline | Sympathetically released NA
76
Which receptors are activated to cause increased for of ventricular contraction?
Beta 1-adrenoreceptors
77
What is an increase in the force of contraction also called?
+ve inotropy
78
What causes an increase in the force of contraction?
VOCC phosphorylation by PKA --> each depolarisation allows in slightly more calcium than usual --> triggers CICR
79
What do sympathetically released NA and some blood-borne adrenaline interact with to cause vasoconstriction?
Alpha 1-adrenoreceptors
80
What causes bronchoconstriction?
Parasympathetic Ach action on M3-muscarinic receptors
81
What causes GI and GU smooth muscle contraction?
A variety of agents on GPCRs
82
What mechanism do all methods of regulation of smooth muscle tone utilise?
Gq-phospholipase C-IP3/Ca2+, DAG/protein kinase C pathways
83
What allows for coordinated increase in contractility of smooth muscle?
Utilisation of the same pathways
84
What often modulates neurotransmitter release in the CNS and PNS?
Pre-synoptic GPCRs
85
What is encephalin?
An endogenous ligand
86
What receptors do morphine and encephalin bind to?
Mu-opioid
87
Which subunit has most affect in the activation of mu-opioid receptors?
G-beta-gamma
88
What action does the g-beta-gamma subunit have?
Causes modulating inhibition of specific types of VOCC (very different to those in the heart)
89
What causes turned down neurotransmitter release?
Decreased calcium influx from specific VOCC modulating inhibition causing reduced vesicle docking
90
What allows for diversity in effector mechanisms of signal transduction?
Range of stimuli Receptors G-proteins Effectors
91
What gives specificity of effector mechanisms in signal transduction?
Specific ligand-receptor interactions Specific G-alpha subunits recruited coupled to particular effector pathways - different between cells but hard wired so that in the same cell type they have the same response
92
What benefit does amplification give to signal transduction?
Allows for gain of control on signalling pathways

Semester 2 (45 decks)

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