Targeting peptide, also known as transport peptide or targeting sequence, is the N-terminal signal of protein synthesized in free ribosomes. Protein is transported, in which chloroplast polypeptide is synthesized on free ribosomes in cytoplasm, separated from ribosome, and folded into protein molecule with tertiary structure.

Signal peptide is a polypeptide that guides the newly synthesized peptide chain to transfer to endoplasmic reticulum. Located at the N-terminal of the newly synthesized peptide chain, it generally has 16~30 amino acid residues and contains 6- 15 positively charged nonpolar amino acids. Because the signal peptide is also the sequence that guides the peptide chain into the endoplasmic reticulum cavity, it is also called the initial transfer sequence.

Components involved in protein synthesis into endoplasmic reticulum