G Protein-Coupled Receptors (GPCRs): Structure, Function, and Signaling Pathways

Question 1

In GPCR signaling, what is the primary role of heterotrimeric G proteins?

Accepted Answer

Transmit signals from GPCRs to effector proteins

Answer

Activate intracellular signaling pathways directly

Answer

Activate GPCRs by hydrolyzing GTP to GDP

Answer

Act as guanine nucleotide exchange factors (GEFs) for GPCRs

Question 2

Which structural feature of GPCRs primarily determines the specificity of ligand binding?

Accepted Answer

Extracellular loops

Answer

Hydrophobic core

Answer

Intracellular loops

Answer

Seven transmembrane domains

Question 3

Which type of G protein couples to the Adenylyl Cyclase (AC) pathway, resulting in increased cAMP production?

Accepted Answer

Gs

Answer

Gi

Answer

Gq

Answer

Go

Question 4

What is the primary role of arrestins in GPCR signaling?

Accepted Answer

To desensitize the receptor and promote its internalization

Answer

To activate the receptor

Answer

To amplify the signal

Answer

To inhibit downstream signaling

Question 5

Which of the following diseases is associated with a mutation in a GPCR gene?

Accepted Answer

Asthma

Answer

Cancer

Answer

Alzheimer's disease

Answer

Multiple sclerosis

Question 6

Which of the following is a competitive antagonist of GPCRs that binds to the same site as the natural ligand?

Accepted Answer

Propranolol

Answer

PGE2

Answer

Insulin

Answer

Epinephrine

Question 7

What is the difference between a GPCR agonist and an inverse agonist?

Accepted Answer

Agonists activate the receptor while inverse agonists inhibit it.

Answer

Inverse agonists activate the receptor while agonists inhibit it.

Answer

Both agonists and inverse agonists activate the receptor.

Answer

Both agonists and inverse agonists inhibit the receptor.

Question 8

Which of the following techniques is commonly used to study the conformational changes of GPCRs?

Accepted Answer

Fluorescence resonance energy transfer (FRET)

Answer

X-ray crystallography

Answer

Patch clamp

Answer

Bioinformatics

Question 9

Describe the key steps in the activation of the MAPK pathway by GPCRs, explaining the roles of G proteins, arrestins, and scaffold proteins.

Accepted Answer

GPCR binding to its ligand triggers conformational changes, activating a G protein. The activated G protein releases its beta-gamma subunits, which activate arrestins. Arrestins recruit scaffold proteins to the GPCR, facilitating the assembly of a signaling complex that activates MAPK.

Answer

GPCRs directly activate MAPK without involving G proteins or arrestins.

Answer

G proteins directly activate MAPK, bypassing the need for arrestins and scaffold proteins.

Answer

Scaffold proteins bind to GPCRs and directly activate MAPK.

Question 10

How do the seven transmembrane helices of GPCRs contribute to their stability and ability to bind ligands?

Accepted Answer

Stability

Accepted Answer

Ligand binding

Answer

Signal transduction

Question 11

Which characteristic is NOT a feature of G Protein-Coupled Receptors (GPCRs)?

Accepted Answer

They possess a small extracellular domain

Answer

They interact with G proteins

Answer

They have seven transmembrane segments

Answer

They are activated upon binding of ligands

Question 12

What is the primary role of G proteins in GPCR signaling pathways?

Accepted Answer

To relay signals from the GPCR to downstream effectors

Answer

To bind ligands and activate GPCRs

Answer

To inhibit GPCR activity

Question 13

What is the downstream effect of Gq protein activation?

Accepted Answer

Activation of phospholipase C, leading to increased intracellular calcium levels

Answer

Inhibition of adenylyl cyclase, resulting in decreased cAMP levels

Answer

Activation of adenylyl cyclase, leading to increased cAMP levels

Question 14

Explain the difference between an agonist and an antagonist in GPCR signaling.

Accepted Answer

An agonist binds to and activates the receptor, while an antagonist binds to and blocks its activation

Answer

An agonist binds to the receptor, but an antagonist does not

Answer

An agonist increases receptor activity, whereas an antagonist inhibits it

Question 15

Which technique is commonly used to study GPCR structure and function?

Accepted Answer

X-ray crystallography

Answer

Mass spectrometry

Answer

Atomic force microscopy

Answer

Gel electrophoresis

Question 16

Which type of G protein is activated by GPCRs?

Accepted Answer

Heterotrimeric G proteins

Answer

Guanylate cyclase

Answer

Small G proteins

Answer

GTPases

Question 17

What is the primary role of the G protein's alpha subunit upon activation?

Accepted Answer

Binding to and activating effector proteins

Answer

Hydrolyzing GTP

Answer

Releasing GDP and binding GTP

Answer

Interacting with the GPCR

Question 18

What is the function of arrestins in GPCR signaling?

Accepted Answer

Desensitizing and internalizing the GPCR

Answer

Activating G proteins

Answer

Inhibiting signal transduction

Answer

Amplifying the signal

Question 19

Which of the following techniques is commonly used to study the structure and function of GPCRs?

Accepted Answer

X-ray crystallography

Answer

PCR

Answer

Western blotting

Answer

Immunohistochemistry

Question 20

What is the role of guanine nucleotide exchange factors (GEFs) in GPCR signaling?

Accepted Answer

Promoting the exchange of GDP for GTP on G proteins

Answer

Activating GPCRs

Answer

Hydrolyzing GTP on G proteins

Question 21

Which structural feature characterizes G Protein-Coupled Receptors (GPCRs)?

Accepted Answer

Seven transmembrane alpha helices

Answer

Extensive glycosylation

Answer

Single transmembrane helix

Answer

Three-dimensional beta-sheet structure

Question 22

What is the primary function of GPCRs?

Accepted Answer

To convert extracellular signals into intracellular responses

Answer

To regulate ion channels

Answer

To produce neurotransmitters

Question 23

Which molecules bind to GPCRs to initiate signal transduction?

Accepted Answer

Ligands

Answer

Antibodies

Answer

Enzymes

Question 24

What is a common mechanism of action for GPCRs?

Accepted Answer

Activation of second messenger pathways

Answer

Stimulation of protein degradation

Answer

Inhibition of gene transcription

Answer

Direct modulation of ion channels

Question 25

What is the main difference between Class A GPCRs and Class B GPCRs?

Accepted Answer

Class A GPCRs bind small molecules, while Class B GPCRs bind large molecules

Answer

Class A GPCRs are heterotrimeric, while Class B GPCRs are homotrimeric

Answer

Class A GPCRs are activated by hormones, while Class B GPCRs are activated by neurotransmitters

Question 26

What role do GPCRs play in sensory perception?

Accepted Answer

Detection of external stimuli, such as light, odor, and taste

Answer

Regulation of metabolism

Answer

Immune system function

Question 27

Which of the following is NOT a potential therapeutic target for GPCRs?

Accepted Answer

Diabetes

Answer

Cancer

Answer

Mental disorders

Answer

Cardiovascular disease

Question 28

Which intracellular protein interacts with GPCRs to terminate signaling?

Accepted Answer

Arrestin

Answer

Ligand

Answer

G protein

Answer

Effector

Question 29

Which technique is commonly used to study the binding of ligands to GPCRs?

Accepted Answer

Radioligand binding assay

Answer

Electromagnetic resonance spectroscopy

Answer

Immunocytochemistry

Answer

Western blotting