If a mutation blocked the function of the signal recognition particle, making it unable to bind signal sequence, what would result?

Question

All proteins would end up in the nucleus.

All proteins would be translated on free ribosomes in the cytoplasm.

All proteins would be secreted from the cell.

All proteins would end up in the mitochondria or chloroplast.

Answer 1

If a mutation blocked the function of the signal recognition particle (SRP), preventing it from binding to the signal sequence, the most likely result would be:

All proteins would be translated on free ribosomes in the cytoplasm.

This is because the SRP is responsible for recognizing and binding to signal sequences on nascent polypeptides that are meant to be translocated into the endoplasmic reticulum (ER) or are destined for secretion. If the SRP is nonfunctional, these proteins would not be directed to the ER; instead, they would continue to be synthesized by free ribosomes in the cytoplasm. Thus, proteins that would normally be sorted to various organelles or secreted would instead remain in the cytoplasm.