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Cell and Molecular Biology > Module 5 Cell Signaling: Signaling through G-Protein-Coupled Receptors > Flashcards

Module 5 Cell Signaling: Signaling through G-Protein-Coupled Receptors Flashcards

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1
Q

are the largest family of cell-surface receptors that mediate responses to external signals, including sight, smell, taste, and cellular communication.

A

G-protein-coupled receptors (GPCRs)

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2
Q

G-protein-coupled receptors (GPCRs) have a single __ that crosses the lipid bilayer __times, forming a __ structure.

A
  • polypeptide chain
  • seven
  • cylindrical
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3
Q

Meanings of GDP and GTP

A
  • guanosine triphosphate (GTP)
  • guanosine diphosphate (GDP)
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4
Q

G-protein-coupled receptors (GPCRs) use G-proteins, specifically __, to relay signals from outside the cell to internal pathways.

A

trimeric GTP-binding proteins

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5
Q

What are the subunits of a G-protein, and their function in an unstimulated state? (3)

A
  • proteins have three subunits: α, β, and γ.
  • In the unstimulated state, the α subunit is bound to GDP, keeping the G-protein inactive.
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6
Q

Upon activation, GPCR acts as a __(__), causing the α subunit to release GDP, bind GTP, and undergo conformational changes.

A

guanine nucleotide exchange factor (GEF)

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7
Q

Upon activation, GPCR acts as a guanine nucleotide exchange factor (GEF), causing the __ subunit to release __, bind __, and undergo conformational changes.

A
  • α
  • GDP
  • GTP
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8
Q

GTP binding causes the __ subunit to dissociate from the __ pair, allowing both the __ to interact with target proteins.

A
  • Gα
  • Gβγ
  • Gα subunit and Gβγ complex
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9
Q

The α subunit is a GTPase and becomes inactive when it __ __ to __, often with the help of RGS (__) proteins.

A
  • hydrolyzes GTP to GDP
  • regulator of G-protein signaling
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10
Q

a large superclass of structurally and mechanistically diverse hydrolytic enzymes, which catalyze the conversion of guanosine triphosphate (GTP) to guanosine diphosphate (GDP) and inorganic phosphate (Pi).

A

GTPases

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11
Q

act as GTPase-activating proteins (GAPs), accelerating GTP hydrolysis in the α subunit to help turn off G-protein-mediated responses.

A

RGS proteins (regulator G-protein signaling)

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12
Q

a second messenger that relays signals from extracellular molecules, such as hormones, to the cell’s interior, leading to various cellular responses.

A

Cyclic AMP (cAMP)/ Cyclic Adenosine Monophosphate

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13
Q

__ synthesizes cAMP from ATP, while __ degrade it, maintaining balance in cAMP levels.

A
  • Adenylyl cyclase
  • cyclic AMP phosphodiesterases
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14
Q

G proteins, such as __(__) and __(__), control the activity of adenylyl cyclase, thereby influencing the levels of cAMP in the cell.

A
  • Gs (stimulatory)
  • Gi (inhibitory)
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15
Q

What effect does the Gs protein have on adenylyl cyclase?

A

activates adenylyl cyclase, increasing the production of cAMP

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16
Q

What is the function of the Gi protein in cAMP regulation?

A

suppresses adenylyl cyclase activity, decreasing cAMP production.

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17
Q

__ causes ADP ribosylation of the Gs α subunit, keeping it active by preventing GTP hydrolysis, leading to excessive cAMP production and severe diarrhea.

A

Cholera toxin

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18
Q

Cholera toxin causes __ of the Gs α subunit, keeping it active by preventing __, leading to excessive cAMP production. The sustained increase in cAMP causes ion and water efflux in __ cells, resulting in severe __ typical of cholera.

A
  • ADP ribosylation
  • GTP hydrolysis
  • intestinal
  • diarrhea
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19
Q

__ ADP-ribosylates the Gi α subunit, locking it in the inactive GDP-bound state, which disrupts its ability to inhibit adenylyl cyclase.

A

Pertussis toxin

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20
Q

Pertussis toxin __ the Gi α subunit, locking it in the __, which disrupts its ability to inhibit adenylyl cyclase.

A
  • ADP-ribosylates
  • inactive GDP-bound state
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21
Q

When cAMP levels rise, different cell types, such as fat cells, may break down __ into __, among other responses.

A
  • triglycerides
  • fatty acids
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22
Q

Some Hormone-induced Cell Responses Mediated by Cyclic AMP: (9)
Given the target tissues, provide the hormones and their major responses.
1) Thyroid gland
2) Adrenal cortex
3) Ovary
4) Muscle
5) Bone
6) Heart
7) Liver
8) Kidney
9) Fat

A

Target tissue / Hormone / Major response
1) Thyroid gland / Thyroid-stimulating hormone (TSH)/Thyroid hormone synthesis and secretion
2) Adrenal cortex / Adrenocorticotrophic hormone (ACTH) / Cortisol secretion
3) Ovary / Luteinizing hormone (LH) / Progesterone secretion
4) Muscle / Epinephrine / Glycogen breakdown
5) Bone / Parathyroid hormone / Bone resorption
6) Heart / Epinephrine / Increase in heart rate and force of contraction
7) Liver / Glucagon / Glycogen breakdown
8) Kidney / Vasopressin / Water resorption
9) Fat / Epinephrine, ACTH, glucagon, TSH / Triglyceride breakdown

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23
Q

What enzyme does cAMP primarily activate to exert its effects in animal cells?

A

Cyclic-AMP-dependent protein kinase (PKA)

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24
Q

What amino acids does PKA phosphorylate on target proteins? (2)

A

Specific serines or threonines.

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25
Q

In the inactive state, PKA consists of a complex of two __ subunits and two __ subunits.

A
  • catalytic
  • regulatory
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26
Q

cAMP activates PKA: cAMP binds to the __ subunits of PKA, causing them to alter their conformation and dissociate from the __ subunits.

A
  • regulatory
  • catalytic
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27
Q

PKA phosphorylates the __ protein, which then recruits this protein to stimulate __ of target genes containing the cyclic AMP response element (CRE).

A
  • CRE-binding (CREB) [cAMP-response element binding protein]
  • transcription
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28
Q

What long-term cellular process is thought to be influenced by CREB activation in the brain?

A

Learning and memory.

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29
Q

Some Cell Responses in Which GPCRs Activate PLCβ: (4)
Given the target tissues, provide each of their signal molecule and major response.
1. Liver
2. Pancreas
3. Smooth muscle
4. Blood platelets

A

Target tissue / Signal molecule / Major response
1) Liver / Vasopressin / Glycogen breakdown
2) Pancreas / Acetylcholine / Amylase secretion
3) Smooth muscle / Acetylcholine / Muscle contraction
4) Blood platelets / Thrombin / Platelet aggregation

30
Q

Which enzyme is activated by G proteins in the phospholipase C-β (PLCβ) pathway?

A

plasma membrane-bound enzyme phospholipase C-β (PLCβ)

31
Q

Which G protein activates phospholipase C-β?

A

Gq

32
Q

What are the two main products of Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) cleavage by phospholipase C-β? (2)

A
  • Inositol 1,4,5-triphosphate (IP3)
  • diacylglycerol (DAG)
33
Q

As a second messenger, __ signaling molecule diffuses through the cytosol to the endoplasmic reticulum (ER), where it binds to IP3-gated Ca²⁺-release channels, increasing cytosolic Ca²⁺ levels.

various cellular processes, including muscle contraction, neurotransmitt

A

inositol phosphate (IP3)

34
Q

In the PLCβ pathway, __ remains in the plasma membrane and activates protein kinase C (PKC), which requires Ca²⁺ for full activation.

A

diacylglycerol (DAG)

35
Q

The rise in Ca²⁺ helps translocate __ to the plasma membrane, where it is activated by Ca²⁺, DAG, and phosphatidylserine.

A

protein kinase C (PKC)

36
Q

A G-protein called __ activates a guanine nucleotide exchange factor (GEF) that activates a __, regulating the actin cytoskeleton.

A
  • G12
  • Rho-family GTPase
37
Q

G proteins can directly activate or inactivate __ in the plasma membrane, affecting cell excitability.

A

ion channels

38
Q

__ activates Gi proteins, opening K+ channels in heart muscle cells, which slows down the heart rate.

A

Acetylcholine

39
Q

__ activate olfactory-specific binding G protein (Golf) proteins, which increase cyclic AMP (cAMP) to open ion channels and generate a signal. It activates adenylyl cyclase.

A

Olfactory receptors

40
Q

Olfactory receptors activate __(__) proteins, which increase cyclic AMP (cAMP) to open ion channels and generate a signal. It activates adenylyl cyclase.

A

olfactory-specific binding G protein (Golf)

41
Q

How many olfactory receptors are there in humans?

A

Approximately 350 olfactory receptors.

42
Q

activate specific olfactory receptors involved in behavioral communication.

A

pheromones

43
Q

What type of cells operate in bright light and is responsible for color vision?

A

Cone photoreceptors (cones)

44
Q

What type of cells operate in dim light and is responsible for noncolor vision?

A

rod photoreceptors (rods)

45
Q

What happens to cyclic GMP levels in rod cells when exposed to light?

A

decreases cyclic GMP levels, closing cation channels and causing hyperpolarization.
- When light hits rhodopsin in rod cells, retinal changes from cis to trans, activating rhodopsin. This activates the G-protein transducin, which in turn activates phosphodiesterase. PDE decreases cyclic GMP (cGMP) levels, leading to the closure of cyclic cation channels, hyperpolarizing the cell and reducing neurotransmitter release, signaling the presence of light.

46
Q

a GPCR, is activated by light and alters the conformation of the G protein transducin, initiating the visual signal.

A

Rhodopsin

47
Q

What enzyme breaks down cyclic GMP in response to light? It is activated by transducing and hydrolyzes cyclic GMP in rod cells.

A

Cyclic GMP phosphodiesterase

48
Q

__ phosphorylates rhodopsin, reducing its ability to activate transducing.

A

Rhodopsin kinase

49
Q

__ binds to phosphorylated rhodopsin, inhibiting its activity and helping terminate the light response.

Phototransduction in Rod Cells

A

Arrestin

50
Q

__ binds to cation channels, keeping them open and allowing ion influx to maintain depolarization.

Phototransduction in Rod Cells

A

Cyclic GMP

51
Q

Rods adapt to changes in light intensity through __ mechanisms, including rhodopsin deactivation and cyclic GMP replenishment, allowing quick adaptation.

A

negative feedback

52
Q

It is a stack of discs in rod cells containing cyclic-GMP-gated cation channels essential for vision in dim light.

A

phototransduction apparatus

53
Q

What happens to cyclic GMP in rod cells when exposed to light?

A

Light-activated rhodopsin changes the conformation of transducin (Gt), activating cyclic GMP phosphodiesterase, which hydrolyzes cyclic GMP, causing its levels to fall.

54
Q

These channels remain open in the dark due to cyclic GMP binding; they close when cyclic GMP levels drop, leading to cell hyperpolarization.

channel and its location

A

cyclic-GMP-gated cation channels in the phototransduction apparatus

55
Q

What is the main function of the Gs family of heterotrimeric G proteins?

A

Activates adenylyl cyclase and Ca²⁺ channels.

56
Q

Which G protein is part of the Gs family and plays a role in olfactory sensory neurons?

what G protein and its definition

A

Olfactory G-protein (Golf); it activates adenylyl cyclase in olfactory sensory neurons.

57
Q

What are the functions of the Gi family of heterotrimeric G proteins?

A

Inhibits adenylyl cyclase and activates K⁺ channels (by the βγ subunits).

58
Q

Which G protein in the Gi family is responsible for activating cyclic GMP phosphodiesterase in vertebrate rod photoreceptors?

A

Gt (transducin)

59
Q

What is the main function of the Gq family of heterotrimeric G proteins?

A

Activates phospholipase C-β.

60
Q

What does the G12/13 family of G proteins do?

A

Activates Rho family monomeric GTPases via Rho GEF to regulate the actin cytoskeleton.

61
Q
  • a small, hydrophobic gas that readily crosses the plasma membrane to signal nearby cells.
  • In mammals, it relaxes smooth muscle in blood vessel walls, leading to vessel dilation.
A

Nitric oxide (NO)

62
Q

How acetylcholine affect nitric oxide synthesis:

Acetylcholine activates a GPCR on endothelial cells, leading to __ synthesis and __ release, which stimulates NO production.

A
  • IP3 (Inositol triphosphate/inositol 1,4,5- triphosphate)
  • Ca²⁺
63
Q

How nitric oxide (NO) affects neighboring cells:

NO diffuses from __ cells into neighboring smooth muscle cells, causing __ of these muscles.

A
  • endothelial
  • relaxation
64
Q

What enzymes produce nitric oxide (NO) from arginine?

A

NO synthases (NOS) enzymes

65
Q

How does nitric oxide (NO) influence guanylyl cyclase?

in muscle function

A

NO binds to iron in guanylyl cyclase, increasing cyclic GMP levels, which leads to muscle relaxation.

66
Q

They depend on relay chains of intracellular signaling proteins and second messengers.

A

GPCR-triggered intracellular signaling pathways

67
Q

How do relay chains of signaling proteins amplify responses to extracellular signals?

A

they amplify cascade of stimulatory signals

68
Q

What are the three modes of adaptation for GPCRs? (3)

A
  1. Receptor sequestration
  2. Receptor down-regulation
  3. Receptor inactivation
69
Q

receptor becomes altered so that it can no longer interact with G proteins

A

receptor inactivation

70
Q

receptor is temporarily internalized to the cell interior, preventing access to its ligand.

A

receptor sequestration

71
Q

It involves the destruction of receptors in lysosomes after they have been internalized.

A

receptor down-regulation

72
Q
  • prevents the activated receptor from interacting with G proteins and serves as an adaptor protein for endocytosis.
  • facilitates receptor-mediated endocytosis.
A

arrestine

Cell and Molecular Biology (8 decks)

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