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Membranes and Receptors > Lecture 3.1: G-Protein Coupled Receptors (GPCRs) > Flashcards

Lecture 3.1: G-Protein Coupled Receptors (GPCRs) Flashcards

1
Q

What is Cell Signalling?

A

The ability to perceive and respond appropriately to ‘information’ in the environment

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2
Q

Principles of Biological Signalling (4 Steps)

A

1) Reception
2) Transduction
3) Response
4) Amplification

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3
Q

What are GPCRs?

A

Membrane bound receptors that utilise G proteins in the transduction process

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4
Q

How many GCPRs does a human have?

A

800-1000 GPCRs

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5
Q

What signals do GCPRs transduce? (4)

A
  • Sensory Information (phototransducers, taste)
  • Hormones
  • Neurotransmitters
  • Growth Factors
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6
Q

What processes do GCPRs play mission critical roles in? (7)

A
  • Neurotransmission
  • Blood Pressure
  • Regulation
  • Vascular Function
  • Glucose Metabolism
  • Immune Response
  • Developmental Processes
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7
Q

Why are GPCRs important in terms of drugs?

A
  • Have been identified as drug targets
  • 1/3 of prescribed drugs act at GPCRs
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8
Q

What drugs act at GCPRs? (5)

A
  • Angiotensin receptor blockers
  • Bronchodilators
  • Anti-histamines for allergy
  • H2 receptor antagonists
  • GPCRs in oncology as they regulate a number of
    signalling pathways in cancer cells
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9
Q

General Structure of GCPRs

A
  • Extracellular N terminus
  • Intracellular C terminus
  • 7 transmembrane α-helices
  • 3 intracellular and 3 extracellular loops
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10
Q

Classification of GCPRs: 2 Types

A
  • Class A-F
  • GRAFS System
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11
Q

Class A of GCPRs

A

Rhodopsin like (includes neurotransmitters and hormones)

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12
Q

Class B of GCPRs

A

Secretin Receptor Family

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13
Q

Class C of GCPRs

A

Metabotropic Glutamate Receptors

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14
Q

Class D of GCPRs

A

Fungal Mating Pheromone Receptors

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15
Q

Class E of GCPRs

A

cAMP Receptors

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16
Q

Class F of GCPRs

A

Frizzled and Smoothened Receptors

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17
Q

GRAFS System

A

Glutamate
Rhodopsin
Adhesion
Frizzled
Secretin

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18
Q

What 3 subunits are G-proteins are made of?

A

α (alpha)
β (beta)
γ (gamma)

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19
Q

How do the α & γ subunits of G-proteins interact with the cell membrane?

A

They are covalently bound via a range of lipid moieties to the membrane – v.complex!

20
Q

At rest GDP (guanosine diphosphate) binds
to what subunit?

A

α-subunit

21
Q

When a ligand binds to the receptor GTP
binds to the α-subunit, what does this cause?

A

Dissociation of the trimer into the α-subunit and a β-γ dimer occurs

22
Q

How many genes code for α?

A

20

23
Q

How many genes code for β?

A

6

24
Q

How many genes code for γ?

A

12

25
Q

How many permutations of G-proteins are possible?

A

c.1400

26
Q

G-Protein Subtype Gs: Effector? Second Messenger?

A

Effector: Adenylyl cyclase (+)
Second Messenger: cAMP ↑

27
Q

G-Protein Subtype Gi: Effector? Second Messenger? (3 of each)

A

Effector:
* Adenylyl cyclase (-)
* K+ channel(+)
* VOCC Ca2+ channel(-)

Second Messenger:
* cAMP↓
* K+↓
* Ca2+ ↓

28
Q

G-Protein Subtype Gq: Effector? Second Messenger?

A

Effector: Phospholipase C (+)
Second Messenger: DAG & IP3 → Ca2+↑

29
Q

G-Protein Subtype Gt: Effector? Second Messenger?

A

Effector: cGMP phosphodiesterase (+)
Second Messenger: cGMP ↓

30
Q

G-Protein Subtype Golf: Effector? Second Messenger?

A

Effector: Adenylyl cyclase (+)
Second Messenger: cAMP ↑

31
Q

What is another name for the G-Protein Subtype Gt? Why is it important?

A
  • Also called transducin
  • Linked to rhodopsin i.e. it transducers photons to
    action potentials
32
Q

What is another name for the G-Protein Subtype Golf? Why is it important?

A
  • Also gustducin
  • Involved in the transduction of taste (bitter, sweet
    and umami)
33
Q

What are protein kinases?

A

Enzymes that when activated phosphorylate substrates

34
Q

What does PKA (Protein Kinase A) target? (3)

A
  • Phosphorylates phosphorylase kinase which in turn
    phosphorylates glycogen phosphorylase leading to
    glycogen breakdown
  • Phosphorylation of Cl- channels in small intestine (Cl-
    enters lumen, Na+ enters lumen = H2O entering n
    lumen)
  • Phosphorylation of transcription factors (e.g. CREB),
    that when phosphorylated are able to initiative
    transcription)
35
Q

How does adrenaline mobilise glycogen breakdown in muscle cells? (6 Steps)

A
  • Chemical Signal: Adrenaline
  • Receptor Activation: β-adrenoreceptor
  • Signal Transduction: Dissociation of G-Protien,
    Activation of adenylyl cyclase
  • Message Generation: ↑ cyclic AMP
  • Enzyme Activation: Activation of PKA, Phosphorylation
    of glycogen phosphorylase
  • Biological Response: Glycogen breakdown
36
Q

Why are Phosphodiesterases important?

A
  • They promote the conversion of cAMP → AMP
    (analogous for cGMP)
  • Their role in ‘switching off’ signalling pathways offers
    the potential for targeting them with drugs
37
Q

Theophylline can inhibit type IV Phosphodiesterases, what effect does this have?

A

Airway relaxation

38
Q

Sildenafil (Viagra) inhibits type ….. Phosphodiesterases, & therefore promotes the vasodilatory effects of
cGMP?

A

V

39
Q

Activation of a muscarinic receptor by acetylcholine

A

Slide 22

40
Q

What is signal amplification?

A

A few molecules of an agonist may evoke significant
intracellular responses

41
Q

Monomeric G-Proteins

A

Often called Small GTPases (to distinguish them from GPCRs) and consist of a single unit (~Gα subunit)

42
Q

What do Monomeric G-Proteins bind at rest?

A

At rest bind GDP, free in cytoplasm

43
Q

How do monomeric G-proteins work? When are they active?

A

Only active when GTP bound (therefore inactivated by GAPs and activated by GEFs)

44
Q

Ras the monomeric G-protein, why is it important?

A
  • Important role (via PKs) in cytoskeletal reorganisation,
    cell polarity, cell cycle progression, gene expression
  • Mutations in Ras genes associated with some 30% of
    tumours
  • Three types of Ras in humans considered to be
    oncogenes
  • Quite often mutations occur in the GTPase region – G-
    protein always on (development of GAPs as tumour
    suppressors?)
45
Q

The process of G-protein insertion and G-Protein degradation is known as…?

A

G-protein trafficking

46
Q

What are GPCRs regulated by?

A

G-protein receptor kinases (GRKs)

47
Q

How do GRKs regulate GCPRs?

A
  • Phosphorylation of activated (ligand bound) GPCRs by
    GRKs allows the binding of β-arrestin proteins
  • Β-arrestins act as scaffolds for endocytosis leads to
    transient receptor internalisation

Membranes and Receptors (19 decks)

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