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EOM Test 3 > GPCRs > Flashcards

GPCRs Flashcards

1
Q

What is the role of intracellular receptors?

A

Signaling molecules for these receptors typically enter the cell by simple diffusion across the plasma membrane or facilitated diffusion

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2
Q

What is the role of cell-surface receptors?

A

Bind signaling molecules that are too large or too hydrophilic to pass through the plasma membrane

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3
Q

What are three ways a cell surface receptor can transmit the signal to the cell?

A
  • Altering the flux of ions across the membrane
  • Turning on enzymatic activity present on the receptor or activating a cytoplasmic enzyme coupled to the receptor
  • regulating the activity of plasma membrane G proteins that are coupled to the receptor
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4
Q

What are three ways ligand-gated ion channels are opened and closed?

A
  • By binding a specific site on the ligand-binding domain
  • intracellular signaling molecules such as cyclic nucleotides and G proteins
  • Phosphorylation by kinases
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5
Q

What are Enzyme-linked receptors?

A

Cell surface receptors that are directly linked to enzymes

Many have a domain that functions as an enzymes

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6
Q

What is the largest family of enzyme-linked receptors that have activity in the cytoplasmic domain?

A

Receptor tyrosine kinases

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7
Q

What are G Protein-coupled receptors?

A

GPCRs are transmembrane proteins that transmit signals by means of intermediary proteins called G proteins

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8
Q

What is the largest family of cell surface receptors in the human genome?

A

GPCRs

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9
Q

What three things do all G protein coupled receptors contain?

A

A membrane-spanning region composed of 7 a-helices

An N-terminal segment and 3 loops on the external surface of the plasma membrane

A cytoplasmic domain that binds to and activates a GTP-binding regulatory protein

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10
Q

Why are G proteins referred to as heterotrimeric proteins?

A

They are composed of three subunits: alpha, beta, gamma

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11
Q

Which two subunits of the heterotrimeric G protein are coupled to the membrane?

A

alpha and gamma

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12
Q

Which two subunits remain coupled during signaling?

A

beta and gamma

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13
Q

How do G proteins act as molecular switches?

A

They are active when GTP occupies the alpha subunit and inactive when it is hydrolyzed to GDP

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14
Q

What are regulator of G protein signaling proteins (RGS)?

A

Proteins that accelerate the intrinsic GTPase activity of the alpha subunit.

Responsible for the rapid inactivation of G protein-coupled signaling

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15
Q

What happens when the alpha subunit is activated?

A

The Ga subunit dissociates from the By subunit and modulates the activity of specific membrane-bound effector proteins

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16
Q

What is the role of the dissociated By subunit after a activation?

A

In some cell types can also interact with effector proteins to transduce a signal

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17
Q

What is adenylyl cyclase?

A

a plasma membrane associated enzyme that catalyzes the conversion of ATP to cyclic AMP (cAMP)

18
Q

What are Gs and Gi?

A

Gs - stimulatory G protein

Gi - inhibitory G protein

19
Q

How is the cyclic AMP signaling pathway activated?

A
  • Extracellular signaling molecule binds to GPCR
  • GPCR GEF activity activates Gsa by replacing GDP with GTP
  • active Gsa associates with and activated adenylyl cyclase
  • AC catalyzes conversion of ATP to cAMP
20
Q

How is the cAMP signaling pathway inactivated?

A

RGS stimulates the intrinsic GTPase activity of Gsa, inactivating

Gsa dissociates from adenyly cylcase, turning it off

21
Q

What is Protein Kinase A and how is it activated?

A

Enzyme composed of 2 regulatory subunits and 2 catalytic subunits.

Activated when cAMP binds the R subunits, causing dissociation and activationof the C subunits

22
Q

What is phosphodiesterase?

A

Metabolizes cAMP to 5’ AMP

This allows the subunits of PKA to reassociate

23
Q

What is the action of PKA?

A

Activates or inhibits enzymes via phosphorylation of serine or threonine

24
Q

What kinds of proteins can PKA activate?

A

Other kinases

Ion channels

Transcription factors

25
Q

What is CREB?

A

cAMP regulatory element binding protein

Once phosphorylated by PKA, binds as a dimer to the cAMP response element (CRE) in the regulatory region of cAMP-inducible genes

26
Q

What is CBP/300?

A

A coactivator protein that links CREB with the basal transcription machinery once CREB is phosphorylated

27
Q

What are A-Kinase Anchoring Proteins (AKAP)?

A

Scaffolding proteins that have one domain that binds to the regulatory subunit of PKA and another that tethers it to a specific subsellular compartment

28
Q

What are two functionsof AKAPs?

A

To limit cAMP-dependent response to a specific subcellular location by tethering PKA to that location.

Can also integrate PKA phosphorylation with other signaling events.

E.g. PDE in the heart muscle

29
Q

What is responsible for inactivating proteins activated by PKA?

A

Protein phosphatases

E.g. Protein Phosphatase 1

30
Q

What is the level of PKA-phosphorylated proteins within a cell determined by?

A

The balance between PKA and protein phosphatase activities

31
Q

Besides PKA, what else can cAMP affect?

A

cAMP can also have a direct effect on ion channels

E.g. gated cation channels in olfactory response

32
Q

What is the effect of forskolin?

A

direct stimulatory effect on adenylyl cyclase

33
Q

What is the effect of caffeine?

A

inhibits phosphodiesterase activity

34
Q

What is isoproterenol?

A

B-adrenergic receptor agonist

35
Q

What is propranolol?

A

B-adrenergic receptor antagonist

36
Q

What type of disorders have been associated with loss-of-function or gain-of-function mutations in Gsa subunits?

A

Rare endocrine disorders

37
Q

What is the function of inhibitory G protein?

A

The a subunit has a direct inhibitory effect on adenylyl cyclase

38
Q

What happens when acetylcholine binds to M2 muscarinic receptor?

A

The By subunits released by Gia activation bind to and open K+ channels. The efflux of K+ hyperpolarizes the plasma membrane

39
Q

What is the mechanism of pertussis toxin?

A

Covalently modifies Gai so that it stays in the G form

40
Q

What are five mechanisms that terminate or diminish the GPCR/cAMP signaling pathway?

A
  • Dissociation/degredation of ligand
  • intrinsic GTPase activity
  • Phosphodiesterase activity
  • Phosphatase action on PKA-phosphorylated proteins
  • GPCR down-regulation

EOM Test 3 (19 decks)

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