Endoplasmic reticulum

Endoplasmic Reticulum, types of endoplasmic reticulum and their functions ,diseases due to malfunctioning of endoplasmic reticulum

1. Endoplasmic Reticulum

2. What is Endoplasmic Reticulum? Endoplasmic - “within the cytoplasm” .Reticulum - Latin for a “a little net ”. extensive network of folded membranes that extends from the nuclear envelope to which it is connected, throughout the cytoplasm . It is present in both, animal and plant cells. divided into two sub- compartments , 1) Rough Endoplasmic Reticulum 2) Smooth Endoplasmic Reticulum

3. Discovery of Endoplasmic Reticulum discovered by Belgian biologist Albert Claude (1899-1983). used the newly developed electron microscope to explore the interior of cells and along with his associate Keith Porter in 1945 observed the presence of a “lace-work structure.”

4. Structure Of Endoplasmic Reticulum Physical Structure: The Endoplasmic Reticulum is 3-dimensional network of intracellular. It is formed of three types of element: 1-Cisternae 2-Tubules 3-Vesicles Cisternae: - These are flattened , unbranched, sac-like element. - They lie in stacks parallel to one another. - They bear ribosomes on the surface

5. Tubules: -These are irregular branching element which form a network along with other element. -These are often free of ribosomes. Vesicles: -These are oval and rounded ,vacuole like element. - These are also free of ribosomes.

6. Molecular structure: The membrane of ER are composed of two layers of phospholipids molecules sandwiched by two layers of proteins molecules like other membrane in the cell wall. Endoplasmic Matrix: The space inside the tubules and vesicles is filled with a watery medium that is different from the fluid in the cytosol outside the ER.

7. Location of Endoplasmic Reticulum There is no specific base or point in a cell, as it extends a network of membranes, tubules, vesicles, and sacs throughout the cell. Endoplasmic Reticulum membranes are folded and stacked on top of each other and connected to the nucleus.

8. Types of Endoplasmic Reticulum: There are two sub- compartments of Endoplasmic Reticulum on the basis of Ribosome , their specific functions and their specific appearance: - Smooth Endoplasmic Reticulum: Ribosomes are ABSENT. - Rough Endoplasmic Reticulum: Ribosomes are PRESENT.

9. Rough Endoplasmic Reticulum: Rough ER- is termed rough because it is studded with ribosomes (the molecules where proteins are made). This is an extensive organelle composed of a greatly convoluted but flattish sealed sac ( cisternae ) that is continuous with the nuclear membrane. In Rough Endoplasmic Reticulum site of synthesis of proteins is destined for secretion.

10. Functions of Rough Endoplasmic Reticulum: The rough endoplasmic reticulum manufactures membranes and secretory proteins . In certain leukocytes (white blood cells), the rough ER produces antibodies . In pancreatic cells, the rough ER produces insulin .

11. The rough and smooth ER are usually interconnected and the proteins and membranes made by the rough ER move into the smooth ER to be transferred to other locations. Ribosomes on the rough endoplasmic reticulum are called ‘membrane bound’ and are responsible for the assembly of many proteins. This process is called translation.

12. The membrane of the rough endoplasmic reticulum forms large double membrane sheets that are located near, and continuous with, the outer layer of the nuclear envelope. It helps in protein translocation, Protein translocation is the process by which peptides are transported across a membrane bilayer.

13. Rough Endoplasmic Reticulum is the starting point of the biosynthetic pathways of: proteins carbohydrate chains phospholipids that journey through the membranous compartments of the cell.

14. Smooth Endoplasmic Reticulum Smooth ER is more tubular than rough ER. Forms a separate sealed interconnecting network. It is found fairly evenly distributed throughout the cytoplasm. It is not studded with ribosomes hence ‘smooth ER’.

15. Functions of Smooth Endoplasmic Reticulum: The network of SER allows increased surface area for the action or storage of key enzymes and the products of these enzymes. The agranular endoplasmic reticulum is the site of lipid synthesis (including oils, phospholipids and steroids) It helps in metabolizing of carbohydrates .

16. It maintains regulation of calcium concentration. In brain cells it synthesizes male and female hormones. In skeletal and cardiac muscle, smooth ER is modified to form sarcoplasmic reticulum i.e. in muscle cells SER stores Ca ions and is known as sarcoplasmic reticulum.

17. SER also help in the biogenesis of Golgi complex n lysosomes . Moreover, it helps in detoxification of drugs and poisons. Which is an important function. It serves as a transitional area for vesicles that transport Endoplasmic Reticulum products to various destinations.

18. The network of smooth endoplasmic reticulum allows for an increased surface area to be devoted to the action or storage of key enzymes and the products of these enzymes It helps in muscle contraction mechanism.

19. Difference in Rough & Smooth Endoplasmic Reticulum

20. Diseases caused by malfunctioning of Endoplasmic Reticulum: ENDOPLASMIC RETICULUM STRESS: The endoplasmic reticulum (ER) is a multifunctional organelle required for lipid biosynthesis, calcium storage, and protein folding and processing. A number of physiological and pathological conditions, as well as a variety of pharmacological agents, are able to disturb proper ER function and thereby cause ER stress, which severely impairs protein folding and therefore poses the risk of proteotoxicity.

21. Proteotoxicity in Endoplasmic Reticulum can cause following diseases in organisms: - Obesity - Diabetes - Oestiogenisis - Aging

22. Books Recommented : Molecular Cell Biology by Bretscher , A . ( 2007 ) Molecular Biology by Weaver, R.F. ( 2005 )