Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : The fluorescence of Green Fluorescent Protein (GFP) occurs without the assistance of any helper molecule or prosthetic group.
Reason (R) : Three amino acids-serine, tyrosine and glycine- in the sequence of GFP react between themselves to form a chromophore that imparts light-transducing capability to GFP.
In light of the above statements, choose the correct answer from the options given below:

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

GFP is a unique protein because it is fully self-sufficient.
Its chromophore (4-(p-hydroxybenzylidene)-5-imidazolinone) forms post-translationally from the internal tripeptide sequence Ser-Tyr-Gly.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Green Fluorescent Protein (GFP) exhibits intrinsic fluorescence upon exposure to blue or ultraviolet light, making it a widely used marker in molecular biology.

Step 2: Detailed Explanation:
The molecular structure of GFP contains a built-in fluorophore located in the center of a \(\beta\)-barrel protein fold.
This internal fluorophore forms spontaneously during protein folding without the addition of helper proteins, enzymes, or cofactors (except molecular oxygen).
The chromophore is synthesized through an autocatalytic cyclization of three contiguous amino acid residues: Serine-65, Tyrosine-66, and Glycine-67 within the primary sequence of the polypeptide chain.
These residues undergo cyclization, dehydration, and oxidation to create the conjugated ring system that acts as the light-absorbing and light-emitting center.
This means Assertion (A) is correct because the protein functions autonomously, and Reason (R) is correct and directly explains why no external cofactor is needed.

Step 3: Final Answer:
Both statements are true and (R) provides the correct physical explanation for (A), as shown in option (A).