The endoplasmic reticulum makes an extensive internal system of membranes in the eukaryotic cells. It makes a system of tubes and sacs that run throughout the cytoplasm. The ER is connected to the nuclear envelop also and serves in the transport of substances and proteins throughout the cells with the help of transport vesicles. For instance, the proteins formed on the surface of rough ER are packed in vesicles that bud off from the surface of rough ER and are carried to the Golgi apparatus for processing.
