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S1 Pharmacology > Extracellular receptor signalling > Flashcards

Extracellular receptor signalling Flashcards

1
Q

what is the purpose of a signal transduction ?

A
  • concerts one form of signal into another one
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2
Q

what are the 3 stages of a signal transduction ?

A
  • extracellular signal activates membrane receptor
  • alters intracellular molecules to be transduced via a certain pathway
  • activates cellular response
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3
Q

what are first and second messengers in signal transduction?

A
  • extracellular signal molecule is the 1st messenger
  • while intracellular molecules are 2nd messenger
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4
Q

What types of chemicals can serve as extracellular signaling molecules (first messengers)?

A
  • steroids
  • peptides + proteins
  • amines
  • small molecules (ions)
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5
Q

What are the four main classes of receptors ?

A
  • Ligand-gated ion channel
  • G-protein coupled receptors
  • Enzyme-linked receptors
  • Nuclear receptors
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6
Q

what are ionotropic receptors + 2 examples ?

A
  • form an ion channel pore
  • type of ligand-gated ion channel
  • Nicotinic acetylcholine receptor = Ach binds to receptor, opens channel for Na+ to enter
  • GABA receptors = allow Cl- to enter, activated by benzodiazepines, inhibitory effect
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7
Q

What are metabotropic receptors?

A
  • indirectly linked with ion channels, usually coupled with G protein
    -eg. muscarin acetylcholine receptor
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8
Q

Compare the speed and duration of response for ionotropic and metabotrophic receptors ?

A
  • metabotrophic is slower but longer lasting response
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9
Q

what is a G-protein coupled receptor (GPCR)?

A
  • A receptor with 7 trans-membrane domains that activates G-proteins
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10
Q

what is the structure of G-protein ?

A
  • made up of α, β, and γ subunits
  • α subunit either has GDP or GTP attached
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11
Q

what happens to the G-protein when GTP binds to the α-subunit?

A
  • when GTP binds to the α-subunit, the α-GTP dissociates from the βγ complex
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12
Q

Explain the G-protein cycle ?

A
  • adrenaline (ligand) binds to β-andrenoceptor
  • causes conformation change = GDP switched for GTP on α subunit
  • α-GTP subunit dissociates
  • α subunit activates adenyl cyclase
  • converts ATP to cAMP which activates PKA
  • GTP hydrolysed by GTPase
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13
Q

How does the G-protein cycle terminate?

A
  • GTPase converts GTP to GDP
  • inactivates protein
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14
Q

what enzyme hydrolyses cAMP (termination of signal transduction ?

A
  • PDE (phosphodiesterase)
  • cAMP coverted to AMP
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15
Q

what substance inhibits PDE ?

A
  • caffeine
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16
Q

How does receptor desensitization reduce signal transduction ?

A
  • PKA phosphorylates β-ARK
  • β-ARK phosphorylates β-adrenoceptor
  • reduces its affinity for adrenaline
17
Q

what is the function of protein phosphatases ?

A
  • remove phosphate groups
  • opposite to kinase
18
Q

what are the 3 main types of G proteins ?

A
  • Gs
  • Gi
  • Gq
19
Q

name a type of receptor that typically couples with Gs proteins.

A
  • β-adrenergic receptors couple with Gs proteins.
20
Q

Name a type of receptor that typically couples with Gi proteins.

A
  • α2-adrenergic receptors couple with Gi proteins
21
Q

What are the two types of Gα subunits that interact with adenylyl cyclase (AC)?

A
  • Gαs: Stimulates AC so inc cAMP
  • Gαi: Inhibits AC so dec cAMP
22
Q

What is the role of Gq proteins ?

A
  • activate phospholipase C (PLC)
  • PLC cleaves PIP2 into IP3 and DAG
23
Q

What are the products of PIP2 breakdown by PLC?

A
  • A: Inositol trisphosphate (IP3) and diacylglycerol (DAG).
24
Q

what is the role of IP3 ?

A
  • iP3 binds to receptors on ER, stimulates ca2+ release
25
Q

What is the function of DAG ?

A
  • DAG remains in the membrane and activates protein kinase C (PKC), which phosphorylates target proteins.
26
Q

do IP3 + DAG remain in membrane ?

A

-DAG hydrophobic so remains
- IP3 water soluble so moves to ER through cytosol

27
Q

what intracellular proteins does calcium bind to and activate?

A
  • Calmodulin (CaM)
  • ## Ca2+-CaM complex activates CaMKs (CaM kinases)
28
Q

what biological process are CaMKs involved in ?

A
  • smooth muscle contraction
29
Q

what is the role of α1 adreno-receptors in blood pressure regulation?

A
  • cause vasoconstriction (smooth muscle contraction) via the Gq-PLC-IP3 pathway
  • increasing blood pressure.
30
Q

How do β2 adrenoceptors affect blood pressure?

A
  • cause vasodilation via the Gs-cAMP-PKA pathway, - decreasing blood pressure.
31
Q

What are the five subtypes of muscarinic receptors and their coupling?

A
  • M1, M3, M5: Gq coupled (stimulatory)
  • M2, M4: Gi coupled (inhibitory)
32
Q

what are the 4 types of enzyme linked receptors ?

A
  • receptor guanylyl cyclases
  • receptor serine/theronine kinase
  • receptor tyrosine kinase
  • receptor tyrosine phosphatase
33
Q

Describe the mechanism of action for receptor guanylyl cyclases + example of response

A
  • ligand binding induces dimerization
  • activates enzyme
  • concerts GTP to cGMP
  • cGMP activates kinases
  • eg. vasodilation
34
Q

Describe the mechanism of action for receptor serine/threonine example of response ?

A
  • ligand binds to type 2
  • type 1 binds to form ternary complex with type 2 and ligand
  • type 2 activates type 1 via phosphorylation
  • type 1 activates / phosphorylates proteins
  • eg. cell proliferation
35
Q

Describe the mechanism of action for receptor tyrosine kinase (RKT) example of response ?

A
  • ligand binding causes receptor to dimersiation
  • both receptors can phosphorylate each other
  • recruit intracellular signal molecules
  • eg. insulin
36
Q

Describe the mechanism of action for receptor tyrosine phosphatase + example of response ?

A
  • only has 1 transmembrane domain so no dimerisation
  • ligand binding activates enzyme
  • dephosphorylate target proteins
  • eg. maturation of lymphocytes

S1 Pharmacology (16 decks)

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