What is the function of signal sequences in proteins?

Signal sequences play a crucial role in ensuring that proteins are correctly routed within the cell. These sequences, typically composed of a short stretch of amino acids, serve as address labels that guide nascent proteins to their appropriate destinations, such as the endoplasmic reticulum, mitochondria, or other organelles within the secretory pathway.

When proteins are synthesized in the ribosome, if they contain a signal sequence, they are recognized by signal recognition particles, which facilitate their transport to the endoplasmic reticulum. From there, proteins can enter the secretory pathway, where they undergo folding, modification, and packaging for secretion out of the cell or for delivery to specific cellular compartments.

Therefore, the primary function of signal sequences is to direct target proteins to the secretory pathway, ensuring that they reach the correct location to perform their functions effectively.