Structure and function
The endoplasmic reticulum is an extensive system of membranes that divides the interior of eukaryotic cells into compartments and channels.
Rough Endoplasmic Reticulum
The Rough ER is very important in the synthesis and packaging of proteins. The proteins synthesized on the surface of the rough ER are exported from the cell. These proteins contain special amino acid sequences called signal sequences. As a new protein is made by a free ribosome, the signal sequence of the growing polypeptide attaches to a recognition factor that carries the ribosome and its partially completed protein to a "docking site" on the surface of the ER. As the protein is made it passes through the ER membrane into the interior ER compartment and moves to the vesicle-forming system called the Golgi complex. It then travels within the vesicles to the inner surface of the plasma membrane, where it is released to the outside. |
Smooth Endoplasmic Reticulum
The smooth ER is more or less the organizer of internal activities. The membranes of the smooth ER contain many embedded enzymes, most of which active only when associated with a membrane. Enzymes anchored inside the ER catalyze the synthesis of a variety of carbohydrates and lipids.In the liver, the enzymes of the smooth ER are involved in the detoxification of drugs including amphetamines, morphine, codeine, and phenobarbital. |