Question

Distinguish between RER and SER on the basis of their structure and function.

Answer 1

Hint: Electron microscopic studies of eukaryotic cells have shown the presence of a network of reticulum of tiny tubular structures scattered in the cytoplasm that is called the endoplasmic reticulum (ER). The endoplasmic reticulum is made of the following three kinds of structures, viz, cisternae, tubules and vesicles.

Complete Answer:
Endoplasmic reticulum is of two types namely rough endoplasmic reticulum and smooth endoplasmic reticulum.
(i) Smooth endoplasmic reticulum (SER): The endoplasmic reticulum which is free of ribosomes is known as SER. When it is observed under the electron microscope it appears as smooth tubular structures.
Function: It is specialised in the synthesis of lipids and steroids. Associated with muscle contraction by release and uptake of $Ca^{+2}$ ions. Synthetic products of RER pass onto Golgi complex through SER.

(ii) Rough endoplasmic reticulum (RER): The endoplasmic reticulum bearing ribosomes on its surface is called RER, it gives a rough granular appearance under the electron microscope. They are extensive and continuous with the outer membrane of the nucleus.
Function: Ribosomes are the site of protein synthesis and thus, RER are present in the cells which are actively involved in the protein synthesis and secretion. It provides precursors of enzymes for the formation of lysosomes in the Golgi complex.
It gives rise to SER.

Sl.No	RER	SER
1.	They are also known as granular ER.	They are also called Agranular ER.
2.	They have ribosomes	They lack ribosomes on its surface.
3.	They are found away from the nucleus in the cell.	They are found towards the nucleus in the cell.
4.	Their function is to synthesize proteins.	Their function is to synthesize lipids
5.	They are present in cells where protein synthesis takes place like plasma cells	They are abundant in those organs which facilitate steroid and acinar cells.
6.	They are involved in the formation of Golgi apparatus.	They are involved in the formation of spherosomes.

Note: RER contains two types of glycoproteins i.e., Ribophorin-1 and Ribophorin-Il for the attachment of 60 S subunit of 80 S ribosome. The muscle cells are also rich in a smooth type of endoplasmic reticulum which is known as sarcoplasmic reticulum.