Endoplasmic Reticulum

The Endoplasmic Reticulum (ER) is a network of flattened, interconnecting tubules which are formed by membranes within the cell. The greater part of the ER is granular, covered by minute dense particles, the ribosomes, on the outside of the membranes which form the tubules. We distinguish between rough or granular ER and smooth or agranular ER. In the former the outer surfaces of the membrane sheets have large numbers of ribosomes attached to them. The smooth or agranular ER have no ribosomes attached to them.

Functions:

• the ER plays a role in the transport of large molecules in the cytoplasm;
• the cavities between the pairs of membrane also serve as storage places for protein;
• it provides a point of attachment for the ribosomes which are the sites of protein synthesis;
• the membranes of the ER are also the sites of fatty acid and other lipid synthesis.