Endoplasmic reticulum-structure and function

1. Shri Shankaracharya Mahavidyalaya, Junwani , Bhilai
Structure & Function of Endoplasmic Reticulum
Dr. Sonia Bajaj
(Head of Department)

2. Introduction
The cytoplasm of most animal cells is an extensive network (reticulum) of membrane-
limited channels, collectively called the endoplasmic reticulum (or ER).
The endoplasmic reticulum was first observed by Garnier and discovered by Claude.
The term ER was given by porter.
The endoplasmic reticulum is present in all eukaryotic cells.
For example, the erythrocytes (RBC), egg and embryonic cells lack in the endoplasmic
reticulum.
Some portion of ER membranes remains continuous with the plasma membrane and
the nuclear envelope.
Fluid present in the lumen of ER is called Endoplasmic matrix.
ER arises as invagination of nuclear membrane.

3. Types of Endoplasmic Reticulum (ER)
Smooth Endoplasmic Reticulum
1. SER closer to plasma membrane.
2. They are also called as the a granular endoplasmic reticulum.
3. They are no Ribosome on its surface so the surface is smooth.
4. The SER are involved in the metabolism of lipids
and glycogen.
Eg. adipose cells, interstitial cells,
glycogen storing cells of the liver.
Rough Endoplasmic Reticulum
1. RER closer to Nucleus.
2. It appears RER contains certain ribosome. A glycoproteins that binds ribosome on ER is
Ribophorins.
3. The rough type of endoplasmic reticulum is found abundantly in those cells which are
active in protein syntheses such as pancreatic cells, plasma cells, goblet cells, and liver
cells.

4. Structure of ER
•The membrane of the endoplasmic reticulum is 50 to 60 Aº thickness.
•The membranes of the endoplasmic reticulum are found to contain many kinds of
enzymes that are needed for various important synthetic activities. The most important
enzymes are the stearases, NADH-cytochrome C reductase, NADH diaphorase, glucose-6-
phosphatase, and Mg++ activated ATPase.
•The membrane of endoplasmic reticulum remains continuous with the membranes of
the plasma membrane, nuclear membrane, and Golgi apparatus.
•The cavity of the endoplasmic reticulum is
well developed and acts as a passage for
the secretory products.
ER consists of Three Elements-
1.Lamellar form or cisternae
2.Vesicular form or vesicle and
3.Tubular form or tubules.

5. The Cisternae
1. The cisternae are long, flattened, unbranched tubular stucture.
2. Diameter is 40 to 50 micrometer.
3. They are always present near nucleus.
4. They are studded with ribosome.
5. Mainly found in protein forming cells.
6. They remain arranged parallelly in bundles or stakes.
Ex. - cells of the pancreas, notochord, and brain.
The Vesicles
1. The vesicles are oval round structures.
2. Diameter is 25 to 500 μm.
3. They are studded with ribosome.
4. Mainly found in protein forming cells.
The Tubules
1. The tubules are branched structures .
2. Forming the reticular system along with the cisternae and vesicles.
3. Diameter from 50 to 190 μm .
4. Tubular form of ER is often found in SER and is dynamic in nature.

6. Functions of ER
1. smooth ER include lipid metabolism .(It Stores Glycogen)
2. Drug detoxification (by the help of the cytochrome P-450).
3.The endoplasmic reticulum provides as skeletal framework to the cell and gives
mechanical support to the colloidal cytoplasmic matrix.
4. The exchange of molecules by the process of osmosis, diffusion and active
transport occurs through the membranes of the endoplasmic reticulum.
5. The endoplasmic membranes contain many enzymes that perform various
synthetic and metabolic activities.
6. The endoplasmic reticulum provides an increased surface for various enzymatic
reactions.
7. The endoplasmic reticulum acts as an intracellular circulatory or transporting
system.
8. ER helps in cell plate formation.