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Y1 - ICPP > Lecture 12 - G Protein Coupled Receptors (Signal Transduction) > Flashcards

Lecture 12 - G Protein Coupled Receptors (Signal Transduction) Flashcards

1
Q

What is Signal Transduction?

A

Its how extracellular signals arrive at cells and cause a response

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2
Q

What must cells have if they want to respond to extracellular signalling molecules?

A

Appropriate receptors

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3
Q

Where can receptors be found?

A

Extracellularly (On plasma membrane)
Intracellularly (Nuclear or in the cytosol)

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4
Q

What are some endogenous agonist ligands that act at Adrenoceptors?

A

Noradrenaline
Adrenaline

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5
Q

What are some Exogneous agonist ligands that act at adrenoceptors?

A

Isoprenaline
Salbutamol (Inhalers)

Propranolol = ANTAGONIST

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6
Q

What is an agonist?

A

Binds to the receptor and activates it

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7
Q

What is an antagonist?

A

Binds to the receptor but does not activate it (BLOCKS ACTION OF AGONISTS)

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8
Q

What anti asthma drug affects GPCRs?

A

Salbutamol

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9
Q

What adrenoceptor does Salbutamol act as an agonist to?

A

B2 adrenoceptor

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10
Q

If a drug has a high affinity for a receptor but no efficacy what does this mean in terms of its action?

A

Antagonist

It binds to the receptor well and blocks it preventing agonists binding to it and acting on it

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11
Q

What B adrenoceptor antagonists can be used to treat hypertension?

A

Propranolol
Atenolol

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12
Q

How many polypeptide chains make up a G protein coupled receptor?

A

1

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13
Q

Where is the N terminal end of the polypeptide chain making up a G-protein coupled receptor?

A

Outside the cell

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14
Q

Where is the C terminal end of the polypeptide chain making up a G-protein coupled receptor?

A

Inside the cell

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15
Q

GPCRs have many different ligands, what are these ligands?

A

Ions
Neurotransmitters
Peptide and non-peptide hormones

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16
Q

Where are the 2 binding sites on the G-protein coupled receptors for ligands?

A

Between 2nd and 3rd transmembrane domain

The N terminal region

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17
Q

How many transmembrane domains are there making up a G protein coupled receptor?

A

7

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18
Q

A GPCR normally sits in an off state, once a ligand binds what happens?

A

A conformational change in shape cause the G Protein associated with it to become activated

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19
Q

What molecule which is bound to a G protein determines whether it is activate or inactive?

A

GTP = On/ACTIVATED
GDP = Off/INACTIVATED

20
Q

How many subunits is a G protein (Guanine-nucleotide binding protein) made up of?

A

3

21
Q

What are the 3 subunits of a G-protein?

A

Alpha (a)
Beta (B)
Gamma (γ)

22
Q

Why are G-proteins described as being heterotrimeric?

A

Made up of 3 different subunits

23
Q

What is the structure of a turned off/inactive G-Protein?

A

Alpha subunit has GDP bound to it
B and γ subunit tightly bound
Alpha and B/γ subunit bound to each other
The subunits all have a high affinity for each other

24
Q

When a ligand (agonist) binds to the GPCR, what happens to the alpha subunit of the G protein and what does this cause?

A

GDP on A subunit is exchanged for GTP

Affinity of the alpha subunit for the B/γ subunit decreases

The A subunit disassociates From the B/γ subunits

25
Q

What happens once the A subunit with GTP bound disassociates from the B/γ subunit?

A

Both the A and B/γ subunit are now activated and can interact with their effector proteins

26
Q

The alpha subunit performs 1 function and the B/γ subunit does ___ function

A

1

27
Q

What enzyme inactivates the G-protein?

A

GTPase

28
Q

How does GTPase inactivate the G-protein?

A

It hydrolyses/removes a phosphate from GTP on the Alpha subunit converting it back to GDP
This makes the A subunit have a high affinity for the B/γ subunit so the rebind to each other again (inactive heterotrimeric complex)

29
Q

How are cellular responses triggered by activation of G proteins?

A

The alpha and the B/γ subunit go on to interact with specific effector proteins leading to the production of second messengers

30
Q

What are the 3 main types of G protein and which subunit is the important part which interacts with the specific effector proteins?

A

Gs
Gi
Gq

Alpha subunit

31
Q

What enzyme (effector protein) do Gs and Gi G-proteins interact with?

A

Adenylyl cyclase

32
Q

What effect does Gs have on the activity of adenylyl cyclase?

A

Stimulates

Gs (s) for (s)timulates

33
Q

What affect does Gs stimulating adenylyl cyclase have on the cell?

A

More cAMP (second messenger) produced
More PKA (Protein Kinase A) activated which activates a range of proteins

34
Q

What effect does Gi have on the activity of adenylyl cyclase?

A

Inhibits

GI (i) for (i)nhibits

35
Q

What affect does Gi inhibiting adenylyl cyclase have on the cell?
What second messenger is produced?

A

Less cAMP (second messenger) produced
Less PKA (Protein Kinase A) activated which activates a range of proteins (less activation happens)

36
Q

What enzyme (effector protein) does the G-protein Gq interact with?

A

Phospholipase C

37
Q

What effect does Gq have on the activity of Phospholipase C?

A

Stimulates it

38
Q

What affect does Gq stimulating Phospholipase C have on the cell?
What second messenger is produced?

A

More IP3 (Inositol triphosphate ) and DAG produced

39
Q

What type of G-protein is associated with B1- adrenoceptors in the heart?
What effector protein is stimulated?
What affect does this have on the heart?
What ligand binds to this GPCR/B1 adrenoceptor?

A

Gs

Adenylyl cyclase

+ve chronotropic affect
+ve inotropic affect

Adrenaline or noradrenaline

40
Q

What type of G-protein is associated with a1- adrenoceptors in the vascular smooth muscle?
What effector protein is stimulated?
What affect does this have on the vascular smooth muscle?
What ligand binds to this GPCR/a1 adrenoceptor?

A

Gq
Phospholipase C
Vasoconstriction
Adrenaline or noradrenaline

41
Q

What type of receptor signalling pathways are interfered with by Cholera toxin (CTx) and Pertussis toxin (PTx)?

A

GPCR G protein signalling

42
Q

How does Cholera toxin interfere with the G protein signalling pathway?

A

Prevents G protein deactivation (continuous effector protein stimulation)

Covalently modifies the Alpha subunit so GTPase cant hydrolyse GTP and deactivate the G protein

43
Q

What effect does the Cholera toxin have by preventing the G protein from being deactivated by GTPase?

A

Effector proteins continuously stimulated (lots of cAMP made) since its a Gs protein

PKA constantly activating the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) which pumps Cl- out of the cell. As a result water follows the chloride

Excess water moved into the gut lumen causing diarrhoea

44
Q

How does Pertussis toxin interfere with G-protein signalling?

What type of G protein is it affecting?

A

Prevents the exchange of GDP with GTP on the alpha subunit

Gi

45
Q

What effect does the Pertussis toxin preventing GDP to GTP exchange on the alpha subunit have?

What type of G protein is it inhibiting from working and therefore what is its affect?

A

G protein never becomes activated and never works on effector proteins

Means process become uncontrolled since the G protein it affects is Gi (less cAMP made)

46
Q

If the GTPase enzyme activity is fast, what effect does this have on the effector protein and levels of second messenger if the G-protein is Gs?

A

Adenylyl cyclase active for less time so less cAMP made

47
Q

If the GTPase enzyme activity is slow, what effect does this have on the effector protein and levels of second messenger if the G-protein is Gs?

A

Adenylyl cyclase enzyme active for more time so more cAMP made

Y1 - ICPP (23 decks)

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