In the visual cycle, photoisomerization of 11-cis-retinal bound to opsin in rod photoreceptors generates all-trans-retinal, which must be converted back to 11-cis-retinal for continued phototransduction. This regeneration occurs primarily in which structure?

• A Mitochondria of the inner segment of the rod cell
• B Outer nuclear layer of the retina
• C Ganglion cell layer of the retina
• D Retinal pigment epithelium adjacent to the photoreceptors ✓

Explanation

After light converts 11-cis-retinal to all-trans-retinal, the chromophore is released from bleached rhodopsin and transported to the retinal pigment epithelium, where retinol dehydrogenases and RPE65 convert all-trans-retinol back to 11-cis-retinal for delivery to rods. Mutations in RPE65 cause Leber congenital amaurosis. The reaction does not occur within the rod mitochondria or the ganglion and outer nuclear layers, making the RPE the sole site of chromophore recycling.

Reference: Ganong's Review of Medical Physiology, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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