ENDOPLASMIC RETICULUM SMG

A brief account of Endoplasmic reticulum and its functions

1. ENDOPLASMIC RETICULUM (ER) Dr. Saji Mariam George Associate Professor (Retired) Assumption College Autonomous Changanacherry

2. ENDOPLASMIC RETICULUM (ER) Cytoplasmic matrix is traversed by a complex network of inter – connecting membrane bound vacuoles or cavities, remain concentrated in the endoplasmic portion of the cytoplasm – hence the name ER. First noted by Porter, Claude and Fullman (1945). Named ER by Porter (1953).

3. Present in almost all eukaryotic cells except ova, embryonic cells and mature RBCs. ER seen in striated muscle cells – ‘ Sarcoplasmic reticulum’ (SR).

4. ER -Transmission electron micrograph

5. Morphology of ER : Three kinds of structures Cisternae – flattened , unbranched sac- like structures arranged in parallel stacks – Diameter 4 to 50 mµ. Bear ribosomes on the surface.

6. b) Tubules Irregular, branched – form a network along with other elements. Diameter 50 to 190 mµ Free of Ribosomes

7. c) Vesicles Oval or round , vacuole – like elements. Occur isolated in the cytoplasm. Free of Ribosomes .

8. Ultrastructure of ER : The cavities of Cisternae , Vesicles and Tubules are bound by a membrane of 50 – 60 A° thickness. The membrane is trilaminar , composed of an outer and inner dense layers of protein sandwiching two layers of phospholipids. The membrane of ER remain continuous with the plasma membrane, nuclear membrane and Golgi complex.

9. Types Of ER : Smooth ( Agranular ) ER [ SER] Devoid of Ribosomes Forms a tubular network Usually lies near the cell membrane Well developed in muscle cells, adipose tissue cells, glycogen storing liver cells etc. SER - Transmission electron micrograph

10. Types Of ER : b) Rough (Granular) ER [ RER] Has Ribosomes attached to its outer surface – makes the surface rough or granular. Found abundantly in cells which are active in protein synthesis – Pancreatic cells, liver cells. The region of cytoplasm containing RER takes basophilic stain- ‘ Ergastoplasm ’. RER - Transmission electron micrograph

11. RER Consists mainly of Cisternae Ribosomes are present on its surface Usually lies deep in the cytoplasm Take part in the synthesis of protein Arises from the nuclear envelope by outfolding . Gives rise to SER. SER Consists mainly of Tubules and Vesicles. Ribosomes are absent on the surface Usually lies near the cell membrane. Take part in the synthesis of lipids, steroids, glycogen. Arises from the RER by the detachment of Ribosomes . Gives rise to Golgi apparatus, Lysosomes and Vacuoles.

12. Functions of ER ER forms an intracellular skeletal frame work to the cell and gives mechanical support to the colloidal cytoplasmic matrix. It facilitates transport of materials from one part of the cell to another. It provides increased surface area for enzyme activity. ER form new nuclear envelope after each nuclear division.

13. 5)RER offers extensive surface for protein synthesis 6) SER provides surface for the synthesis of cholesterol, lipids, steroid hormones, glycogen etc. 7) SER produces Golgi apparatus, Lysosomes and Vacuoles.

14. THANK YOU