Which of the following statements correctly describes the function of a signal peptide?

Question

BlackTom AI · Accepted Answer

Let’s analyze each statement in turn to understand what a signal peptide does and does not do.
Option 1: 'It helps target a protein to the ER.' This is accurate. A signal peptide, typically at the N-terminus of a nascent polypeptide, is recognized by the signal recognition particle (SRP), which pauses translation and guides the ribosome-protein complex to the ER membrane where the protein can be translocated into the ER lumen or membrane. This aligns with the canonical role of signal peptides in directing secretory pathway proteins to the endoplasmic reticulum.
Option 2: 'It directs an mRNA molecule into the lumen of the ER.' This is not correct. The signal peptide acts on the nascent polypeptide, not on the mRNA itself. The mRNA is located in the cytoplasm and translated by ribosomes; the targeting signal is on the emerging peptide, which then interacts with the SRP and the translocon at the ER.
Option 3: 'It terminates translation of messenger RNA.' This is inaccurate. Translation termination is governed by stop codons and release factors, not by signal peptides. Signal peptides are about targeting and translocation, not halting translation.
Option 4: 'It signals the initiation of transcription.' Transcription initiation occurs in the nucleus with transcription factors and RNA polymerase, not through peptide-level targeting signals. A signal peptide functions post-translationally, during translation, to direct the growing polypeptide to the ER, not to initiate transcription in the nucleus.
Overall, the statements differ in whether they correctly attribute the signal peptide’s role to targeting a protein to the ER, versus misattributing actions to mRNA localization, translation termination, or transcription initiation. The only option that accurately captures the signal peptide’s function is the first one, since it directly describes its role in guiding proteins into the endoplasmic reticulum pathway.

Which of the following statements correctly describes the function of a signal peptide? 单项选择题

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