In addition to other jobs, the endoplasmic reticulum creates and folds proteins and then carries these synthesized substances to the Golgi apparatus via the vesicles. The endoplasmic reticulum also executes sorting activities for the cell's proteins. However, the precise duties carried out by the endoplasmic reticulum vary by both species and cell type.
All cells are composed of numerous, smaller components commonly called organelles; the endoplasmic reticulum is one such organelle. Other examples of organelles include the nucleus, the mitochondria and the Golgi apparatus. The endoplasmic reticulum is one of the largest organelles in most cells and also plays a large role in maintaining the cell's shape.
Two primary parts make up the endoplasmic reticulum: a cytoskeleton and numerous sac-like features called cisternae. There are two types of endoplasmic reticulum; one is called the smooth endoplasmic reticulum, while the other is called the rough endoplasmic reticulum. The primary difference between the two types is that rough endoplasmic reticulum carries a number of ribosomes on its surface, while the smooth endoplasmic reticulum does not. However, as these ribosomes attach and release from the endoplasmic reticulum over time, smooth sections can become rough and vice versa; this happens as the cell's metabolic needs change.