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Highly hydrophobic amino acid sequences of proteins that must cross through membranes to arrive at their functioning cellular location (such as secreted and membrane proteins). They are 15 to 60 amino acids long and reside at the amino-terminus (leader signal peptides) or internally. By binding to signal recognition particles, these sequences direct nascent protein-ribosome complexes to a membrane where the protein is inserted during translation. Signal peptides direct translational uptake of the protein by various membranes -endoplamic reticulum, mitochondrial, chloroplast, peroxisomal, etc. Leader signal sequences on non-membrane proteins are ultimately removed by specific peptidases.