Question

Differentiate between rough and smooth endoplasmic reticulum. How is the endoplasmic reticulum important for membrane biogenesis?

Answer 1

Hint: The endoplasmic reticulum is an important organelle of the cell that helps in protein production as well as in their transportation processes. The rough endoplasmic reticulum is involved in the synthesis of proteins by the presence of ribosomes over their surface. Some of the endoplasmic reticulum in cells do not have ribosomes.

Complete answer: Endoplasmic reticulum or ER is one of the major organelles present in eukaryotic cells that help in protein and fat production and transportation. It is made up of a network of membranes and is present just beside the nucleus of the cell. Cells that produce large amounts of proteins and oils have a large number of ER present in them. The ER is divided into two types based on its structure or physical appearance.
a) Rough endoplasmic reticulum
b) Smooth endoplasmic reticulum

The basic and the most observable difference between the Rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER) is the presence or absence of ribosomes over its surface. The ER that has ribosomes attached to its membrane is called Rough ER because they appear to be rough in structure due to the irregular presence of ribosomes over them. But the SER does not have any ribosomes over them which makes them smoother in appearance. Furthermore, the RER is made up of cisternae and few tubules, whereas the SER is made up of vesicles and tubules. The RER is majorly involved in proteins and enzymes production. But the SER majorly synthesizes glycogen, lipids, and steroids. The RER is situated more internally to SER and is connected with the nuclear envelope. On the other hand, the SER is peripheral to RER and may be connected with the plasmalemma. Also, it is thought that RER develops from nuclear envelope and SER is a modification of RER and thus, it is developed from RER.
Now as we know that ER synthesizes many proteins, lipids, and steroids in the cell. These products are used in making up the plasma membrane. Besides, the process of formation of the plasma membrane is known as membrane biogenesis. Thus, the ER plays a vital role in the process of membrane biogenesis.

Note: Almost every type of eukaryotic cell consists of ER as its important organelle. But some cells do not contain it. For example, red blood cells do not contain ER. Only cells that take part in oil and protein synthesis have Endoplasmic reticulum in them.