Principles of Biochemistry (2+1)

1.1.3.4 Endoplasmic reticulum (ER)

Endoplasmic reticulum(ER) is a vast system of interconnected, membranous, infolded and convoluted sacks that are located in the cell's cytoplasm (the ER is continuous with the outer nuclear membrane). They are of two types: Rough endoplasmic reticulum and Smooth endoplasmic reticulum.  

 i)Rough endoplasmic reticulum (rough ER): Rough ER is covered with ribosomes that give it a rough appearance. Rough endoplasmic reticulum bears the ribosomes during protein synthesis. The newly synthesized proteins are sequestered in sacs, called cisternae. The system then sends the proteins via small vesicles to the golgi apparatus. In the case of membrane proteins it inserts them into the membrane

ii) Smooth endoplasmic reticulum (smooth ER): Smooth ER buds off from rough ER. The space within the ER is called the ER lumen. Smooth endoplasmic reticulum  transports the proteins manufactured by the rough endoplasmic reticulum to other locations in the cell or outside the cell. This is achieved through a process called budding, wherein the small vesicles, which contain proteins, are detached from the smooth endoplasmic reticulum and are carried to other locations. This cell organelle also aids in converting glucose-6-phosphate to glucose, which is an important step in gluconeogenesis.