Question

The reaction of 11-cis-retinal with the lysine residue of a specific protein forms the light-sensitive pigment in the cells of retina. The light-sensitive pigment is an

• A. amide
• B. acid
• C. anhydride
• D. imine

Hint:

In biochemistry, imine bonds are formed between an aldehyde and an amine, such as in the formation of rhodopsin.

Answer 1

The Correct Option is D

Step 1: Understanding the chemical reaction.
In the retina, 11-cis-retinal reacts with the lysine residue of a specific protein, forming a light-sensitive pigment called rhodopsin. This reaction results in the formation of an imine bond between the aldehyde group of 11-cis-retinal and the amine group of the lysine residue.

Step 2: Analyzing the options.
(A) amide: Incorrect — An amide is formed by a reaction between a carboxyl group and an amine, not in the case of retinal.
(B) acid: Incorrect — The reaction does not result in the formation of an acid.
(C) anhydride: Incorrect — An anhydride would be formed through a different type of reaction, usually between two acids.
(D) imine: Correct — The reaction forms an imine, which is a compound where a nitrogen atom is double-bonded to a carbon, typically formed between an amine and an aldehyde.

Step 3: Conclusion.
The correct answer is (D) imine, as this is the type of bond formed between retinal and the protein in the retina.