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pharmacology > G protein coupled receptors > Flashcards

G protein coupled receptors Flashcards

1
Q

what type of receptors are the acetylcholine muscarinic receptors ?

A

G protein coupled receptors

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2
Q

how long does it take for GPCR to affect a cells physiology ?

A

seconds

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3
Q

what are they mainly involved in ?

A

fast synaptic transmission

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4
Q

6 steps to chemical signalling ?

A
  1. agonist synthesis
  2. agonist release
  3. transport
  4. detection by a target cell via receptor
  5. physiological response
  6. signal inactivation and end of response
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5
Q

what is agonist ?

A

an intercellular ( outwith the cell) signal that activates a receptor and elicits a response.

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6
Q

what is the GPCR resting state ?

A

the effector enzyme , agonist , GDP and not in contact

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7
Q

what occurs when the agonist binds ?

A

this brings the receptor , GTP , effector and agonist into close contact. The enzyme activity is altered and the second messengers are produced

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8
Q

what is the structure if the GPCR ?

A

it has 7 transmembrane domains that are embedded in the plasma membrane. There is an extracellular N domain , an intracellular C domain as well as a 3rd intracellular loop that interacts with the G protein.

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9
Q

once G protein are active are they diffusible ?

A

yes

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10
Q

why is the G protein called a heterotrimeric ?

A

it is composed of 3 subunits , alpha , beta and gamma

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11
Q

what type of activity does the alpha subunit have ?

A

GTPase

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12
Q

what occurs when an agonist binds ?

A

this causes the bound GDP to exchange to GTP , no phosphorylation occurs it is just an exchange. Then the heterotrimeric G protein dissociates as the alpha subunit dissociates while the beta and gamma are still stable and bound. It is these subunits that go onto interact with various enzymes and their target.

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13
Q

what subunit associates with the GDP or GTP ?

A

the alpha subunit

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14
Q

describe Gs protein ?

A

this is composed of αs β γ. It stimulates the effector enzyme adenylcyclase and leads to cAMP second messenger being increased and protein kinase A is target.

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15
Q

describe Gi protein ?

A

αi β γ this inhibits the effector enzyme adenyl cyclase and this decreases the second messenger cAMP as well as protein kinase A activation.

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16
Q

describe Gq ?

A

αq β γ this activates effector enzyme phospholipase C which increases the second messengers DAG and IP3

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17
Q

what G proteins regulate adenylcyclase activity ?

A

Gi and Gs

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18
Q

what are effectors ?

A

these are enzymes that produce intracellular signal molecules ( within cell) called secondary messengers.

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19
Q

is cAMP diffusible and what is it’s target ?

A

yes , protein kinase A

20
Q

what does PKA do ?

A

phosphorylate other targets such as metabolic enzymes , transcription factors and CREB

21
Q

what is cAMP ?

A

a cyclic nucleotide that contains adenine. It is produced from ATP and enzyme adenylcyclase

22
Q

what is cGMP ?

A

it is structurally similar to cAMP but has guanine as it’s base. It is produced by the guanylyl cyclase.

23
Q

what word describes the short period of time of cyclic nucleotides ?

A

transient increase in them

24
Q

in order to control the concentrations of cAMP , what 2 enzymes are available ?

A

adenyl cyclase - produce cAMP

phosphodiesterase’s - degrade cAMP

25
Q

how do phosphodiesterases work and what do they produce ?

A

they break the cyclic ring , the produce AMP and GMP. These are both biologically inactive and are not secondary messengers.

26
Q

how does cAMP regulate transcription?

A

cAMP activating the PKA which phosphorylates CREB a protein and transcription factor , that is bound to CRE ( cAMP responsive element ) and this is an enhancer found in cAMP regulated genes. The CBP ( CREB binding protein) is then recruited to the transcription complex and transcription is initiated.

27
Q

what is the effector enzyme phospholipase C regulated by ?

A

Gq

28
Q

what does the enzyme do ?

A

it cleaves specific membrane phospholipids to produce 2 secondary messengers DAG and IP3

29
Q

what is PIP2 and what happens to it ?

A

phosphatidylionositol-4,5-bisphosphate cleaved to produce secondary messengers

30
Q

DAG full name ?

A

1,2-diacylglycerol

31
Q

IP3 full name?

A

inostitol-1,4,5-triphosphate

32
Q

where is DAG found , can it move and what is it’s target ?

A

found in the plasma membrane where it stays , it has a target of protein kinase C.

33
Q

where is protein kinase C located ?

A

in the cytoplasm , so the DAG brings it up to the cytoplasm

34
Q

describe IP3 ?

A

it is a freely diffusible water soluble mediator

35
Q

target of IP3 and what occurs next ?

A

when binds to target of IP3 receptor it activates it and intracellular stores of ca2+ are released within seconds

36
Q

what activates PKA ?

A

cAMP

37
Q

activates PKC ?

A

DAG

38
Q

protein kinase G ?

A

cGMP

39
Q

what do the kinase enzymes recognise ?

A

the short amino acid ‘target’ on specific Serine/Threonine and add a phosphate.

40
Q

what do the phosphatase’s do ?

A

they remove the phosphate group

41
Q

is the activity of an effector enzyme independent or dependent of the receptor occupation ?

A

dependent , it needs to be activated by an agonist.

42
Q

once the second messsenger’s are produced are they slowly cleared or rapidly ?

A

rapidly

43
Q

what is a key role of second messengers ?

A

signal amplification.

44
Q

what regulates the effector enzymes ?

A

the alpha subunit

45
Q

what happens when an agonist is present ?

A

causes the GPCR cycle to occur faster , if not present then it still occurs but at a slower rate.

46
Q

how is the signal terminated ?

A

• GTPase activity of G protein
• Removal (or degradation) of second messenger
• ‘Inactivation’ of the receptor (by phosphorylation)
• Desensitisation of effector enzyme
(thereby reducing second messenger production)
• Protein kinases and phosphatase activities

pharmacology (21 decks)

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