Signal peptides target some eukaryotic polypeptides to specific destinations in the cell. Two populations of ribosomes, free and bound, are active participants in protein synthesis. ○ Free ribosomes are suspended in the cytosol and synthesize proteins that reside in the cytosol. ○ Bound ribosomes are attached to the cytosolic side of the endoplasmic reticulum (ER) or to the nuclear envelope. Bound ribosomes synthesize proteins of the endomembrane system as well as proteins secreted from the cell. Although bound and free ribosomes are identical in structure, their location depends on the type of protein they are synthesizing. Translation in all ribosomes begins in the cytosol, but a polypeptide destined for the endomembrane system or for export has a specific signal peptide region at or near the leading end. o The signal peptide consists of a sequence of about 20 amino acids. A signal recognition particle (SRP) binds to the signal peptide and attaches it and its ribosome to a receptor
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This note was uploaded on 01/04/2012 for the course BSC BSC1005 taught by Professor Orlando,rebecca during the Fall '10 term at Broward College.