ENDOPLASMIC RETICULUM INTRODUCTION • Light microscopists described filamentous structures ergatoplasm • The name endoplasmic reticulum was first used by Porter and Kallman. • Found in all animal and plant cells, except in mature erythrocytes and prokaryocytes . • Since this network is more concentrated in the endoplasm of the cytoplasm, the name endoplasmic reticulum was proposed. • Cytoskeleton of the cell. Occurrence • The occurrence of ER varies from cell to cell • Lack of ER: The erythrocytes (RBC), egg and embryonic cells. • Poorly developed ER: The spermatocytes • SER: the adipose tissue, brown fat cells and adrenocortical cells, interstitial cells of testes and cells of corpus luteum of ovaries, sabaceous cells and retinal pigment cells. • RER: Cells actively engaged in the synthesis of proteins such as acinar cells of pancreas, plasma cells, goblet cells, and cells of some endocrine glands. • Both SER & RER: Hepatocytes • The RER is located around the nucleus in the cells of both plants and animals. • It transports proteins and lipids throughout the cell. • The SER is connected to the nuclear envelope of cells in plants and animals. • It's primary function is to facilitate the metabolism of carbohydrates and Steroids • The endoplasmic reticulum is made out of a lipid membrane. • It is still connected to the nuclear membrane that is wrap around the cell’s DNA. • So there is a straight connection between the cells nucleus and the endoplasmic reticulum. Morphology • Consists of three components: 1. Cisternae (ర్నట ె 졁) – secretary cells 2. Vesicle (ఆశ밾졁 (逿త్తు졁)) – pancreatic cells 3. Tubules (ꀾ찿క졁) – Non –secretary cells 1. Cisternae The cisternae are long, flattened, sac-like, un branched tubules having the diameter of 40 to 50 µm. • They remain arranged parallely in bundles or stakes. • RER usually exists as cisternae • They have ribosomes on their surface • They are abundant in cells which are active in protein synthesis. 2. Vesicles • The vesicles are oval, membrane bound vacuolar structures having the diameter of 25 to 500 µm • They often remain isolated in the cytoplasm and occur in most cells but especially abundant in the SER. • Abundant in liver and pancreatic cells. 3. Tubules • The tubules are branched structures forming the reticular system along with the cisternae and vesicle. • They usually have the diameter from 50 – 100 µm • Occur almost in all the cells. • Often found in SER, present in non-secretary cells like striated muscles Smooth ER • Possesses smooth walls, there are no ribosomes attached to the membrane surface. (Tubules, vesicles) • SER mostly occur, those cells which are involved in the metabolism of lipids and glycogen. • Found in adipose cells, interstitial cells, glycogen storing cells of the liver, conduction fibres of heart, spermatocytes and leucocytes. • SER in muscle cells known as Sarcoplasmic reticulum. • SER in the pigmented retinal cells known as Myeliod bodies • An arrangement of tubules, vesicles • Synthesizes lipids • Well developed in cells synthesize steroid hormones. • Makes membrane lipids, carries proteins detoxifies drugs Rough ER • The RER possesses rough walls because the ribosomes remain attached with its membrane. • Mainly consists of Cisternae • Ribosome play a vital role in the process of protein synthesis. • RER present in: Pancreatic cells, plasma cells, goblet cells and liver cells. • The RER takes basophilic stain due to its RNA content of ribosomes. Chemical composition • Mainly composed of lipoproteins,lipids - lecithin, cephalin, spingomyelin • Nucleotide diphosphatase • NADH – Cytochrome C reductase • Mg++ activated ATP-ases • Sucrases • Several carrier enzymes – transport substances Origin of ER Palade stated that – it may be originated as the infoldings of plasma membrane . ER may be formed from the evagination of nuclear membrane, through the formation of annulate lamellae (Gay 1955, Rebhun 1956) Functions of ER Mechanical Support – 밾త్ర逿క ఆ鰾ర롁 Permeability - ꠾రగమ్య త Transport – ర퐾ణా (త్రరరణ) Protein synthesis – మ కృత్తల ల శ్లషే ణ Synthesis of Cholesterol and Steroid Hormones Detoxification – ꀿ퐿� కరణ롁 (퐿ష రత롁 桇뱁ట ) Lipid synthesis – 젿꠿葍 ల శ్లషే ణ Glycogenolysis - 屍లలైే ల్ Storage of Ca++ ions – Ca++ అ밾ꁁల ꀿ졁వ Reference Books: Cell Biolohy – C.B. Power Cell Biology Verma Agarwal I Year zoology Telugu Academy Text Book Web Links: www.biologydictionary.net https://byjus.com/biology/eukaryotic-cells/ www.biologydiscussion.com www.toppr.com www.biologydiscussion.com www.microscopemaster.com .