Biological Systems MCAT Practice Exam 2025 – The Comprehensive All-in-One Guide for Exam Success!

When a photon is absorbed by opsins, the retinal chromophore undergoes a significant structural change as part of the phototransduction process. Specifically, upon the absorption of light, the 11-cis-retinal form of retinal is converted to all-trans-retinal. This conversion is a crucial step in the visual cycle, as the change in shape to all-trans-retinal triggers a series of biochemical reactions that ultimately lead to changes in the electrical signals sent to the brain, allowing the perception of light.

The conversion from 11-cis-retinal to all-trans-retinal initiates the activation of the opsin protein, leading to the activation of a G-protein (transducin) and subsequent signaling cascades in the photoreceptor cells. This process is essential for vision, as it allows the conversion of light stimuli into neural signals.

Therefore, the statement that retinal converts to all-trans-retinal when a photon is absorbed reflects the correct understanding of the molecular basis of vision.