Question

What kind of receptor is rhodopsin, which does not respond to neurotransmitter molecules?

• A. C-protein coupled receptor
• B. G-protein coupled receptor
• C. M-protein coupled receptor
• D. n-protein coupled receptor

Hint:

Even though GPCRs are famous for neurotransmission, some function as sensory receptors. Rhodopsin is the classic evolutionary example of a light-activated GPCR.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the biological classification of the light-sensitive receptor protein rhodopsin.

Step 2: Detailed Explanation:

• Rhodopsin is the photopigment located in the outer segment of rod cells in the retina, responsible for dim-light vision.

• Structurally, rhodopsin belongs to the superfamily of G-protein coupled receptors (GPCRs), characterized by seven transmembrane domains.

• Unlike typical GPCRs in the nervous system that are activated by chemical ligands (neurotransmitters), rhodopsin is activated by light (photons).

• When light strikes the 11-cis-retinal cofactor inside rhodopsin, it isomerizes to all-trans-retinal, causing a conformational change in the opsin protein.

• This conformational change activates a specialized G-protein called transducin, initiating the visual phototransduction cascade.

• There are no standard categories named "C-protein," "M-protein," or "n-protein" coupled receptors in standard neurobiology.

Step 3: Final Answer:
Rhodopsin is structurally and functionally classified as a G-protein coupled receptor (GPCR).