An extra-peptide extension found at the amino terminus of a nascent protein, and functions by prompting the transport mechanism within the cell to bring it to its specific destination within the cell, i.e. the endoplasmic reticulum into the secretory pathway
Signal peptide, commonly comprised of a chain of approximately 20 amino acids, is essential because it directs the protein where it should go. If the protein is for secretion (transport outside the cell), then, the signal peptide is necessary to direct the protein to the endoplasmic reticulum where it will grow further and mature to ready for secretion. The signal peptide is recognized by the signal recognition particle (SRP) and cleaved by the signal peptidase following transport at the endoplasmic reticulum.