What is the endoplasmic reticulum?
The endoplasmic reticulum (E.R.) synthesizes proteins for export from the cell. The rough E.R. gets its name for the rough appearance of ribosomes on its surface. The E.R. is the site where lipid components of the cell membrane are assembled, along with proteins and other materials that are exported from the cell. The portion of the E.R. involved in the synthesis of proteins is the rough E.R. The other portion of the E.R., the smooth E.R., is smooth because ribosomes are not attached to it. In many cells, the smooth E.R. contains collections of enzymes that perform specialized tasks.