Question

One of the roles of the RNA component of signal recognition particle (SRP) is to stimulate certain proteins to hydrolyze GTP. If this function of SRP RNA did not work properly, what would you expect to happen? a. SRP would not bind to the ER signal sequence of a polypeptide. b. SRP would not cause translation to pause. c. SRP would not bind to an SRP receptor in the ER membrane. d. SRP would not be released from the ER membrane. e. both a and b

Short answer

The most likely consequences of SRP RNA not functioning properly would be the scenarios from Option C and Option D. This is because both are part of the process involving GTP hydrolysis, which is the primary role of the SRP RNA.

Step-by-step solution

Understanding SRP RNA Role

SRP RNA serves the purpose of stimulating proteins to carry out the hydrolysis of GTP. This is an important energy-related activity within the cell.

Analyzing Option a

If SRP did not bind to the ER signal sequence of a polypeptide as stated in Option A, it means proteins would not be directed to the endoplasmic reticulum (ER) for processing. But the binding action is not directly related to GTP hydrolysis; thus this option is not the correct consequence of malfunctioning SRP RNA.

Analyzing Option b

Option B suggests that SRP would not cause translation to pause. This is a primary step in protein synthesis, which isn't directly related to the GTP hydrolyzing function of SRP RNA. Thus, this option is also not the correct consequence of malfunctioning SRP RNA.

Analyzing Option c

Option C suggests that SRP would not bind to an SRP receptor in the ER membrane. The binding of SRP to its receptor triggers the hydrolysis of GTP, enabling the loading of the protein into the ER. Thus, if the SRP RNA fails to function properly, this scenario could indeed occur.

Analyzing Option d

Option D implies that SRP would not be released from the ER membrane. Releasing SRP from the membrane does occur as part of the GTP hydrolysis cycle, making this option a possible consequence of malfunctioning SRP RNA.

Analyzing Option e

Option E implicates both Option A and B, but as already outlined these options do not correlate with malfunctioning SRP RNA.

Key concepts

RNA function

RNA (Ribonucleic Acid) is crucial for many cellular processes. In the context of the Signal Recognition Particle (SRP), RNA plays a significant role in protein synthesis and targeting. The RNA component of SRP acts by enhancing the efficiency of protein interactions.
Specifically, it promotes the hydrolysis of GTP, a molecule that provides the energy required for these interactions. Without the proper function of RNA within the SRP, this critical energy-dependent process would be compromised.
This would lead to:

• Inefficient protein targeting to the correct cell locations.
• Improper processing and folding of proteins.

Therefore, malfunctioning RNA in the SRP can disrupt proper protein synthesis and targeting.

GTP hydrolysis

GTP hydrolysis is the process of breaking down GTP (Guanosine Triphosphate) into GDP (Guanosine Diphosphate) and a phosphate group. This reaction releases energy, essential for several cellular functions.
In the case of the SRP, GTP hydrolysis facilitates the binding and release of the SRP from the SRP receptor. This is a key step during protein targeting to the endoplasmic reticulum.
If SRP RNA is unable to stimulate GTP hydrolysis properly, it can lead to:

• SRP not binding properly to the SRP receptor.
• Failed release of SRP after delivering the targeted protein.
• Disruption in the overall protein translocation process.

Thus, GTP hydrolysis is fundamental to the proper operation of the SRP mechanism.

Protein targeting

Protein targeting is a vital process that ensures proteins reach their correct cellular destinations. In eukaryotic cells, the SRP plays a crucial role in guiding proteins to the endoplasmic reticulum (ER).
The SRP binds to a signal sequence on the nascent protein, pausing translation, and directs the protein to the ER membrane. Once at the ER, GTP hydrolysis facilitates the interaction of the SRP with its receptor.
This ensures a smooth transfer of the protein for further processing and folding. If this targeting process is inefficient due to faulty SRP RNA or disrupted GTP hydrolysis, proteins may:

• Not localize correctly within the cell.
• Misfold, leading to cellular dysfunction.

Proper targeting is critical for maintaining cellular function and structure.

Endoplasmic reticulum

The endoplasmic reticulum (ER) is an essential organelle in eukaryotic cells. It plays a pivotal role in the synthesis, folding, modification, and transport of proteins.
There are two types of ER: rough and smooth. Rough ER is studded with ribosomes and is primarily involved in protein synthesis. The SRP directs new proteins to the rough ER for processing.
Once proteins are targeted to the ER, they are folded and modified into their functional forms. A properly functioning SRP is essential for this process, as it ensures that proteins reach the ER effectively.
Any interruption in SRP function can lead to:

• Proteins being sent to incorrect locations.
• Accumulation of misfolded proteins, potentially causing diseases.

Therefore, the ER's interplay with SRP is crucial for cell health and function.