The Question is from neet-botany cell-biology , and it was created by the author Mr. NARESH KUMAR K

Question

Which of the following statements regarding the signal recognition particle (SRP) and its receptor is INCORRECT?

Mr. NARESH KUMAR K · Accepted Answer

## CORE INFORMATION
✓ **Answer**: [D]
## CONCEPT FRAMEWORK
**Primary Concept**: Signal Recognition Particle (SRP) and Protein Targeting
**Related Topics**: Protein synthesis, endoplasmic reticulum (ER) translocation, signal sequences
**Prerequisites**: Basic understanding of protein synthesis, membrane protein trafficking
## SOLUTION PATHWAY
**Given Information**:
    * Question asks for the INCORRECT statement about SRP and its receptor.
    *  We need to evaluate each statement against our understanding of SRP function.
**Method & Steps**:
    1. Analyze statement A: 'The SRP receptor is an integral membrane protein of the ER.'
        Reasoning: SRP receptor is indeed located on the ER membrane and is required for docking of the SRP-ribosome complex.
        Formula/Rule: None
    2. Analyze statement B: 'SRP binds to both the signal sequence and the ribosome, halting translation.'
        Reasoning: SRP recognizes the signal sequence as it emerges from the ribosome and binds to it, also interacting with the ribosome. This interaction does halt translation.
        Working: None
        Key Point: This is a key step in targeting proteins to the ER.
    3. Analyze statement C: 'SRP guides the ribosome-mRNA complex to the ER membrane.'
        Reasoning: Once bound to the SRP, the ribosome-mRNA complex is indeed guided to the ER membrane via interaction with the SRP receptor.
        Working: None
        Key Point: This is the targeting function of SRP.
    4. Analyze statement D: 'SRP binds to the nascent polypeptide chain only after it has completely emerged from the ribosome.'
        Reasoning: SRP binds to the signal sequence as it emerges from the ribosome, not after it's completely emerged. This early binding is critical for targeting.
        Working: None
        Key Point: The signal sequence emerges during translation and is recognized early.
    5. Identify the incorrect statement.
        Result: Statement D is the incorrect one.
        Verification: All other statements are consistent with the known function of SRP.
## OPTION ANALYSIS
[A] :x: This statement is correct. The SRP receptor is indeed an integral membrane protein of the ER.
[B] :x: This statement is correct. SRP binds to the signal sequence and the ribosome, causing translation to pause.
[C] :x: This statement is correct. SRP guides the complex to the ER membrane.
[D] ✓: This statement is incorrect. SRP binds to the nascent signal sequence as it emerges from the ribosome, not after the polypeptide is completely synthesized.
## LEARNING AIDS
**Common Mistakes**:
    1. [Error 1]: Confusing SRP binding with post-translational translocation. SRP binding occurs co-translationally.
        [How to avoid]: Remember SRP binds to the signal sequence as it is being translated, not after.
    2. [Error 2]: Thinking SRP only binds to the signal sequence. SRP interacts with both the signal sequence and the ribosome.
        [How to avoid]: Understand that SRP has multiple binding domains.
**Quick Tips**:
    1. [Helpful shortcut]: Remember that SRP's role is to halt translation temporarily and target the ribosome to the ER.
    2. [Memory aid]: Think of SRP as a 'traffic controller' for ribosomes with ER-targeting proteins.

Mr. NARESH KUMAR K · Answer

The SRP receptor is an integral membrane protein of the ER.

Mr. NARESH KUMAR K · Answer

SRP binds to both the signal sequence and the ribosome, halting translation.

Mr. NARESH KUMAR K · Answer

SRP guides the ribosome-mRNA complex to the ER membrane.

Mr. NARESH KUMAR K · Answer

The correct Option is "SRP binds to the nascent polypeptide chain only after it has completely emerged from the ribosome."

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