All proteins are synthesized by ribosomes in the cell. some ribosomes float freely in the cytosol, while others are bound to the surface of the endoplasmic reticulum. most proteins made by free ribosomes function in the cytosol. proteins made by bound ribosomes either function within the endomembrane system or pass through it and are secreted from the cell. which of the following proteins are synthesized by bound ribosomes?

Ost proteins that function in the cytosol (such as actin) or in the nucleus (such as DNA polymerase) are synthesized by free ribosomes. Proteins that function within the endomembrane system (such as lysosomal enzymes) or those that are destined for secretion from the cell (such as insulin) are synthesized by bound ribosomes.
As a protein destined for the endomembrane system is being synthesized by a ribosome, the first amino acids in the growing polypeptide chain act as a signal sequence. That signal sequence ensures that the ribosome binds to the outer membrane of the ER and that the protein enters the ER lumen.