Final answer:
After a protein reaches its cellular destination, the targeting signal sequence is usually clipped off, similar to a train ticket being taken after a journey. In some cases, the signal peptide might remain if it is functionally integral to the protein's final structure or involved in further processes.
Step-by-step explanation:
Once a protein reaches its destination within the cell, the targeting signal it carries has two main possibilities. The protein may have a signal sequence, typically at the N-terminal end consisting of 10-30 amino acid residues, which is necessary for directing the protein to its destination. After fulfilling its role, this signal sequence is commonly removed or clipped off. This is analogous to a train ticket being taken at the end of a journey. In some cases, however, the signal peptide may remain if it forms an integral part of the protein's final functional structure or is involved in additional cellular processes.