Endoplasmic Reticulum (ER) PDF

Endoplasmic Reticulum (ER) nucleus  The endoplasmic reticulum (ER) is a network of flat and vesicular structures which extends throughout the cytoplasm in animal cells. These sacs and tubules are all interconnected by a single continuous membrane so that the organelle has only one large...

Endoplasmic Reticulum (ER) nucleus  The endoplasmic reticulum (ER) is a network of flat and vesicular structures which extends throughout the cytoplasm in animal cells. These sacs and tubules are all interconnected by a single continuous membrane so that the organelle has only one large, highly convoluted and complexly arranged lumen (internal space).  It takes up aproximately 12% of the total volume of a cell. It is connected to the double-layered nuclear envelope. the SER are formed from RER by loss of ribosomes. Intercisternal space of ER is continuous with perinuclear space.  Structure The Endoplasmic Reticulum (ER) is a part of the Endomembranous system and is a membrane bound organalle. The membrane of endoplasmic reticulum is 50-60 Å thick. The rough endoplasmic reticulum is connected to the outer membrane of the nucleus.  Structure When we look at the ultrastructure of E.R., it is composed of three types of elements. 1- Cisternae : These are narrow, flattened and unbranched structures generally present near the nucleus. They lie parallel to each other and may be interconnected. They occur in the cells having active synthetic roles.  Tubules : Tubules are wider, tubular and irregulary branched elements mainly present near the cell membrane. Each tubule is about 50-100μm diameter. These are without ribosomes and are actively involved in glycogen metabolism, lipid and steroid synthesis.  Vesicles : These are spherical or oval bodies scattered in the cytoplasm whose diameter ranges from 25-500 μm.  Types of endoplasmic reticulum I/ Smooth Endoplasmic Reticulum (SER) also called as the agranular endoplasmic reticulum. This type of endoplasmic reticulum possesses smooth walls because the ribosomes are not attached to its membranes.  The smooth type of endoplasmic reticulum occurs mostly in those cells, which are involved in the metabolism of lipids (including steroids) and glycogen. Eg. adipose cells, glycogen storing cells of the liver, spermatocytes, and leucocytes. II/ Rough Endoplasmic Reticulum (RER) It possesses rough walls because the ribosomes are attached to its membranes. The rough type of endoplasmic reticulum is found abundantly in those cells which are active in protein synthesis such as pancreatic cells, plasma cells, goblet cells, and liver cells.  Functions Functions of smooth ER include lipid metabolism (they synthesize a variety of phospholipids, cholesterol, and steroids). Glycogenolysis (degradation of glycogen). Drug detoxification (by the help of the cytochrome P-450). Functions of rough ER As a growing secretory polypeptide emerges from the ribosome, it passes through the RER membrane and gets accumulated in the lumen of RER. Here, the polypeptide chains undergo tailoring, maturation, and molecular folding to form functional secondary or tertiary protein molecules.  Transportation:RER is involved in collection and transportation of synthesized proteins and forms transport vesicles which carry the material like proteins to the cisternae of Golgi bodies for their condensation into secretory vesicles.