Question

Which one of the following correctly describes the role of signal recognition particles?

• A. Aid in the decoding of the information carried by the signal peptide for the secretory protein.
• B. Aid in recognizing the antigen for inflammatory response.
• C. Aid in receiving coated vesicles for exocytosis.
• D. Aid in deciphering the genetic code for protein synthesis.

Hint:

Think of the SRP as a postal worker for the cell. It reads the 'zip code' (the signal peptide) on a newly made protein and ensures it gets delivered to the correct 'address' (the endoplasmic reticulum).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The Signal Recognition Particle (SRP) is a crucial component in the cellular machinery for protein targeting. It is a ribonucleoprotein complex that recognizes and directs proteins destined for the secretory pathway (e.g., to be secreted, inserted into membranes, or targeted to certain organelles) to the endoplasmic reticulum (ER).

Step 2: Detailed Explanation:
The process, known as co-translational targeting, occurs as follows:
1. A ribosome begins translating an mRNA molecule. If the protein is destined for the secretory pathway, a specific N-terminal amino acid sequence called the 'signal peptide' emerges from the ribosome.
2. The SRP recognizes and binds to this signal peptide. This binding event causes a pause in translation.
3. The entire complex (SRP, ribosome, nascent polypeptide) is then targeted to the ER membrane, where SRP binds to an SRP receptor.
4. The ribosome docks with the translocon (a protein channel in the ER membrane), translation resumes, and the growing polypeptide chain is threaded through the channel into the ER lumen.
In essence, the SRP 'decodes' the signal peptide, interpreting it as a 'mail address' for the ER.

Step 3: Analyzing the Options:
- (A) Aid in the decoding of the information carried by the signal peptide for the secretory protein: This accurately describes the primary function of SRP. It recognizes the signal peptide and initiates the targeting process.
- (B) Aid in recognizing the antigen for inflammatory response: This is the function of immune system components like antibodies and T-cell receptors.
- (C) Aid in receiving coated vesicles for exocytosis: This process involves proteins like SNAREs, which mediate vesicle fusion with the plasma membrane.
- (D) Aid in deciphering the genetic code for protein synthesis: This is the fundamental role of the ribosome and transfer RNAs (tRNAs).

Step 4: Final Answer:
Option (A) provides the most accurate and specific description of the role of the Signal Recognition Particle.