Endoplasmic Reticulum (cell biology)

● ENDOPLASMIC RETICULUM 

1. Endoplasmic reticulum was discovered by Porter in 1945. 

2. ER consists of a complex membraneous system in the cytoplasm of eukaryotic cells. 

3. ER is absent in prokaryotes and matured erythrocytes of mammals. 

4. The cytoskeleton of cell is made up of endoplasmic reticulum, microtubules, microfilaments and intermediate filaments. 

5. Under electron microscope three principal forms of endoplasmic reticulum are visible. They are: 

• cisternae 

• vesicles 

• tubules 

6. The Endoplasmic Reticulum (ER) is divided into two broad categories: 

• Rough Endoplasmic Reticulum (RER) 

• Smooth Endoplasmic Reticulum (SER) 

7. Both types of ER compose a system of membranes that enclose a space.

8. The space enclosed within its membranes is termed the tuminal or cisternal space, the region outside of the membranes is the cytosolic space. 

9. RER possesses rough wall because ribosomes remain attached on the surface with the help of ribophorins. 

10. RER is specially well developed in cells actively engaged in protein synthesis. 

11. Ribosomes are not attached with the membrane of SER. 

12. SER is related with the synthesis and metabolism of lipids or steroids. 

13. Sarcoplasmic reticulum found in skeletal and cardiac muscles is highly modified form of SER. 

● Origin 

• Membranes of ER resemble with nuclear membrane. 

• ER membranes form new nuclear envelope after each nuclear division. 

● Functions of Endoplasmic Reticulum 

• Mechanical Support: ER provides an ultrastructural skeletal framework to the cell. 

• Exchange of Molecules: The exchange of molecules by process of osmosis, diffusion and active transport occurs through membranes of ER. 

• Intracellular Impulse: Sarcoplasmic reticulum conducts intracellular impulse in muscles. 

• Nuclear Membrane Origin: ER membrane forms new nuclear membrane after cell division. 

• Protein Synthesis: This is the most important function of rough ER. 

• Lipid Synthesis and Storage: SER is related with steroid and lipid synthesis and storage. 

• Glycogen Metabolism: glycogenolysis. 

• Detoxification: SER possesses detoxifying enzymes (oxygenase) including cytochrome P450s present generally in liver cells. 

• Muscle Contraction: SER is associated with release and uptake of Ca+ ions during muscle contraction. SER is related with