biology : class11 G Protein-Coupled Receptors : Receptors, Second Messengers, Gene Regulation : Hormone Action MCQ Questions and Answers
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G Protein-Coupled Receptors
MCQ questions and answers.
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MCQ Questions
1. What is a characteristic feature of a G protein-coupled receptor (GPCR)?
A.
It spans the cell membrane seven times
B.
It is found only inside the nucleus
C.
It is made of DNA
D.
It has no connection with cell signaling
Correct Answer:
It spans the cell membrane seven times
Explanation:
GPCRs are membrane proteins that typically cross the plasma membrane seven times and help transmit signals from outside the cell to the inside.
2. Where is a G protein-coupled receptor mainly located?
A.
In the plasma membrane
B.
In the nucleolus
C.
Inside the ribosome
D.
In the mitochondrion only
Correct Answer:
In the plasma membrane
Explanation:
GPCRs are located in the plasma membrane, where they bind signaling molecules outside the cell.
3. What usually binds to the outside part of a GPCR?
A.
A signaling molecule or ligand
B.
A ribosomal protein
C.
A chromosome
D.
A digestive enzyme
Correct Answer:
A signaling molecule or ligand
Explanation:
A ligand binds to the extracellular part of a GPCR and changes the receptor's shape, beginning a signaling process.
4. Which protein is directly associated with the inner side of a GPCR?
A.
A heterotrimeric G protein
B.
A collagen fiber
C.
A DNA polymerase
D.
A structural cellulose protein
Correct Answer:
A heterotrimeric G protein
Explanation:
GPCRs interact with heterotrimeric G proteins on the cytoplasmic side of the plasma membrane.
5. What happens to a G protein when a ligand activates a GPCR?
A.
GDP is replaced by GTP on the alpha subunit
B.
GTP is replaced by DNA
C.
The receptor leaves the cell permanently
D.
The G protein becomes a ribosome
Correct Answer:
GDP is replaced by GTP on the alpha subunit
Explanation:
Activation of a GPCR promotes the exchange of GDP for GTP on the G protein alpha subunit, activating the G protein.
6. Which molecule commonly acts as a second messenger in a GPCR signaling pathway?
A.
Cyclic AMP
B.
Hemoglobin
C.
Cellulose
D.
Keratin
Correct Answer:
Cyclic AMP
Explanation:
Cyclic AMP, or cAMP, is a common second messenger produced after activation of certain GPCR pathways.
7. Which enzyme can be activated by a G protein to produce cyclic AMP?
A.
Adenylyl cyclase
B.
Pepsin
C.
DNA ligase
D.
Amylase
Correct Answer:
Adenylyl cyclase
Explanation:
Activated G proteins can stimulate adenylyl cyclase, an enzyme that converts ATP into cyclic AMP.
8. What is the main role of a second messenger in a GPCR pathway?
A.
To carry the signal inside the cell
B.
To form the cell wall
C.
To store genetic information
D.
To digest food outside the cell
Correct Answer:
To carry the signal inside the cell
Explanation:
Second messengers such as cAMP relay and amplify the signal from an activated GPCR within the cell.
9. Which subunit of a heterotrimeric G protein binds GDP or GTP?
A.
Alpha subunit
B.
Beta subunit only
C.
Gamma subunit only
D.
Receptor sugar chain
Correct Answer:
Alpha subunit
Explanation:
The alpha subunit of a heterotrimeric G protein binds GDP in its inactive state and GTP in its active state.
10. What generally happens when the ligand is removed from an activated GPCR pathway?
A.
The signaling pathway returns toward its inactive state
B.
The GPCR changes into DNA
C.
The cell membrane is permanently destroyed
D.
The receptor produces unlimited signals
Correct Answer:
The signaling pathway returns toward its inactive state
Explanation:
When the ligand is no longer present, G protein activity decreases and the GPCR signaling pathway is switched off or reduced.
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