What is the chromophore of all 3 types of cones?

• A. 11-cis retinal
• B. All-trans retinal
• C. 11-cis retinol
• D. Retinal Schiff base

Answer: (A)

Light detection in cones relies on a chromophore that is 11-cis retinal. Each cone type has its own opsin, giving different wavelength sensitivities, but all share this same retinal chromophore. When a photon is absorbed, 11-cis retinal isomerizes to all-trans retinal, triggering the change in opsin that initiates the phototransduction cascade. Afterward, all-trans retinal is released and recycled back to 11-cis retinal to prepare for more light. The other options aren’t correct because all-trans retinal is what you get after absorption, not the resting chromophore; 11-cis retinol isn’t the photopigment’s chromophore; and retinal Schiff base refers to the bond between retinal and opsin, not the chromophore itself.