A system of membranes within the cytoplasm of plant and animal cells. It forms a link between the plasma and nuclear membranes (see cisterna) and is the site of protein synthesis. It is also concerned with the transport of proteins and lipids within the cell. Rough ER has ribosomes attached to its surface; proteins synthesized on the ribosomes are enclosed in vesicles and transported to the Golgi apparatus. Smooth ER lacks ribosomes; it is the site of important metabolic reactions, including phospholipid and fatty-acid synthesis.
Subjects: Biological Sciences — Chemistry.