This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Initiation of visual impulse is associated with: 
Select and explain. 
A. Condensation of opsin with vitamin A aldehyde, B. Photoisomerization and hydrolysis of visual purple, C. INADP, D. I NAD
B: Photoisomerization and hydrolysis of visual purple
Answer: B: Photoisomerization and hydrolysis of visual purple 
Explanation: When light falls on rhodopsin, it is absorbed by rhodopsin causing isomerization of the retinaldehyde from 11-cis to all-trans form, and a conformational change in opsin. This results in the release of retinaldehyde from the protein, and the initiation of a nerve impulse. The final step is hydrolysis to release all-trans-retinaldehyde and opsin. Ref: Harper's Illustrated Biochemistry, 28th Edition, Page 44