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 – 밾త్ర逿క ఆ鰾ర롁

 Permeability - ꠾రగమ్య త

 Transport – ర퐾ణా (త్రరరణ)

 Protein synthesis – మ కృత్తల ల శ్లషే ణ

 Synthesis of Cholesterol and Steroid Hormones

 Detoxification – ꀿ퐿� కరణ롁 (퐿ష రత롁 桇뱁ట )

 Lipid synthesis – 젿꠿葍 ల శ్లషే ణ

 Glycogenolysis - 屍లలైే ల్

 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