Final answer:
Retinal is the nonprotein molecule necessary for rhodopsin to detect light, undergoing a transformation from a cis to a trans form in response to light, enabling the detection and transduction of the visual signal.
Step-by-step explanation:
Rhodopsin, a photoreceptor crucial for vision in vertebrates, consists of a trans-membrane protein called opsin and a vital nonprotein molecule called retinal. When light interacts with retinal, it induces a change in its shape from a bent cis form to a straighter trans form, a process called photoisomerization. This change prompts the activation of a G-protein known as transducin, initiating a cascade of events that ultimately result in the hyperpolarization of the photoreceptor cell membrane and the closure of sodium channels.
The nonprotein molecule essential for rhodopsin to detect light is retinal, which is derived from vitamin A. Retinal undergoes a transformation in response to light exposure, switching from 11-cis-retinal to all-trans-retinal. This transformation reactivates rhodopsin, allowing it to continuously aid in the detection of light and thereby support the normal vision of the eye.