What determines the ultimate destination of a protein?

Signal sequences are short peptide sequences found at the beginning, or sometimes embedded within, a protein that dictate the protein's ultimate destination within the cell. These sequences act like postal codes that guide proteins to specific locations, such as the nucleus, mitochondria, or the endoplasmic reticulum.

The presence of these signal sequences allows cellular machinery to recognize and transport proteins appropriately. For example, proteins meant for the mitochondria will have specific mitochondrial targeting sequences, while those destined for secretion might have a signal peptide that directs them to the endoplasmic reticulum.

Other factors like pH levels, temperature signals, or amino acid length may influence protein structure, function, or stability, but they do not directly determine the end location of the protein within the cell. Ultimately, it is the presence of specific signal sequences that serves as the primary determinant for protein trafficking and localization.