Endoplasmic reticulum is a complex membrane lined network of flattened sacs, tubules and vesicles that runs throughout the cytoplasm of eukaryotic cells from plasma membrane to nuclear envelope. The ER was first noted by Porter, Claude and Fullman in 1945. It was named ER by Porter in 1953. It is absent in Prokaryotes but present in all the eukaryotes except germinal cells and mature mammalian erythrocytes.
In mature cells, ER occurs in two forms: rough (RER) and Smooth(SER)
Functions of Endoplasmic Reticulum (Common to SER and RER)
- The membranous network of endoplasmic reticulum provides mechanical support.
- ER membranes possess sites for a number of enzymes and cytochromes to carry out specific reactions.
- The larger surface area is useful for rapid synthesis of biochemicals.
- It holds various cell organelles in their position.
- With the help of desmotubules, ER of one cell communicates with ER of adjacent cells.
- It conducts information from outside to inside of cell and between different organelles of the same cell.
- ER function as circulating system of the cell for quick transport of materials.
- It forms vacuoles.
- During telophase, part of the nuclear envelope is formed by endoplasmic reticulum.
- ER provides membranes to golgi bodies for production of vesicles and Golgian vacuoles.
- It provides precursors to Golgi bodies for complexing and elaboration of biochemicals for internal use as well as secretion.