Final answer:
The sorting signal for protein sorting is a sequence of amino acids at the protein's N-terminal or C-terminal that directs it to a specific location within the cell, which is often removed upon arrival.
Step-by-step explanation:
The sorting signal used in protein sorting is a short tail of amino acids that directs a protein to a specific cellular compartment. These signal sequences can be located either at the amino end (N-terminal) or the carboxyl end (C-terminal) of the protein, acting as a "train ticket" for proteins to reach their ultimate destination within a cell.
Cellular factors recognize these signals and facilitate the transport of the protein from the cytoplasm to the correct compartment, such as the mitochondria or chloroplasts (in plants). Typically, once the protein arrives at its destination, the signal sequence is removed.