How are proteins regulated after translation?
A proteins that are no longer required can be transported out of the cell
B inactive proteins can be activated by phosphorylation
C active proteins can be inactivated by post-translational modification
D fewer mRNA molecules can be transcribed to produce fewer proteins
E proteins can be tagged with ubiquitin molecules and subsequently degraded
The correct answer and explanation is :
The correct answer is E) Proteins can be tagged with ubiquitin molecules and subsequently degraded.
Explanation:
After translation, proteins undergo various regulatory mechanisms to ensure cellular functions are appropriately controlled. One of the key processes that regulate protein activity and lifespan is the ubiquitin-proteasome pathway. Here’s a breakdown of how it works and why option E is correct:
- Ubiquitination and Degradation:
Proteins that are no longer needed or that are damaged can be tagged with a small protein called ubiquitin. This process is known as ubiquitination. Once a protein is tagged with multiple ubiquitin molecules, it is recognized by the proteasome, a large protease complex in the cell. The proteasome then unfolds and translocates the protein into its catalytic core, where it is broken down into smaller peptides. This mechanism is crucial for regulating protein levels and removing malfunctioning proteins. Therefore, option E is correct, as it describes how proteins can be marked for degradation. - Phosphorylation for Activation (Option B):
While it is true that phosphorylation can activate proteins by adding phosphate groups, this is a separate mechanism. Phosphorylation typically alters the protein’s conformation, making it active or inactive depending on the context. However, this is not directly about protein degradation, which is the focus of option E. - Inactivation by Post-Translational Modification (Option C):
Post-translational modifications, such as phosphorylation, acetylation, or glycosylation, can indeed modify the activity of proteins. However, inactivation via modification is not the same as degradation, which is why this option doesn’t focus on the major regulatory pathway of protein removal. - Transcriptional Regulation (Option D):
Regulating mRNA transcription affects how much protein is synthesized but does not directly impact the regulation of proteins after translation. Post-translational mechanisms like ubiquitination are key for managing the fate of proteins already produced.
Thus, option E most accurately describes a critical mechanism for protein regulation after translation.