hard · MCAT
In the human eye, the conversion of a physical light stimulus into a neural signal begins in the retina.
Which of the following best describes the initial photochemical event and the subsequent signal transduction mechanism?
- Retinal isomerizes from 11-cis to all-trans, activating a G-protein-coupled receptor cascade.
- Opsin undergoes a conformational change that directly releases neurotransmitters without second messengers.
- Photon absorption triggers the phosphorylation of retinal by a receptor tyrosine kinase.
- Retinal isomerizes from all-trans to 11-cis, leading to the direct opening of sodium channels.
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