Class 11 note || Structure and functions of endoplasmic reticulum:
Introduction:
Endoplasmic reticulum is an extensive series of interconnecting membranous cannals in the cytoplasm of the eukaryotic cell. Endoplasmic reticulum is continuous with the outer nuclear membrane,Golgi apparatus and more probably with the cell membrane.
There is present a fluid medium in the lumen of the endoplasmic reticulum, known as endoplasmic matrix. The diameter of the lumen is about 400-700 Angstrom.
Types of endoplasmic reticulum:
There is present two types of endoplasmic reticulum : rough endoplasmic reticulum and smooth endoplasmic reticulum.
Rough endoplasmic reticulum:
Rough endoplasmic reticulum is so called because the membrane of this part is dotted with embeded granules organelles called ribosomes ,giving the rough endoplasmic reticulum a bumpy appearence .
The endoplasmic reticulum can be identified by its morphology as well -it often consists of convoluted, flattened sac like structures that originate near the nucleus.
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| Rough endoplasmic reticulum, Image by- |
fd's Flickr Toys, source, License-CC BY 2.0
Structure of the rough endoplasmic reticulum:
Morphologically the endoplasmic reticulum can be divided into two structures namely - cisternae and sheets.
A large number of sheets present in the structure of the endoplasmic reticulum. The sheets are a two dimensional array of flattened sacs that across the cytoplasm. Translocon,an important protein complex, which is also present in the rough endoplasmic reticulum ,is necessary for the protein translation within the rough endoplasmic reticulum.
Cytoskeletal elements especially the microtubules is also present in the structure of RER. The structure of the RER is dependent on the structure of the microtubule . If there is any temporary disruption in the structure of the microtubule ,then ER network collapse and reforms only after the cytoskeleton are reestablished.
If there is any change in the pattern of microtubule polymerization then the ER morphology also changes. In addition when the ribosomes detach from the sheets of the rough endoplasmic reticulum,these structures can disperse,and leads to the formation of tabular cisternae.
Functions of the rough endoplasmic reticulum:
1.The rough endoplasmic reticulum is concerned with the synthesis of proteins.
2. Rough endoplasmic reticulum is also involves in the transport of protein.
3. Disulphide bond formation .
4. Rough endoplasmic reticulum is also involves in the degradation of worn-out organelles like mitochondria.
5.Membrane synthesis.
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Smooth endoplasmic reticulum :
It is the endoplasmic reticulum with smooth appearance. On the surface of the smooth endoplasmic reticulum there is not present any ribosomes. Smooth endoplasmic reticulum is also known as tubular endoplasmic reticulum because it is formed by many interconnected tubules.
Structure of the smooth endoplasmic reticulum:
Primarily the smooth endoplasmic reticulum is composed of three-dimensional polygonal networks of tubules called cisternae.
The smooth endoplasmic reticulum is also dynamic in nature,with new tubules budding off from the sides of existing structures. The cytoskeletal elements actin and microtubule is involved in the extent of the of smooth endoplasmic reticulum.
With the help of the motor proteins ER tubules can slide along the cytoskeletal framework.
In muscle cells and neurons,smooth endoplasmic reticulum has a great significance.
In muscle cells the smooth endoplasmic reticulum is known as sarcoplasmic reticulum and is an important site for the storage of calcium ions.
Functions of smooth endoplasmic reticulum:
1.Smooth endoplasmic reticulum is responsible for the synthesis of non protein substances such as steroids and cholesterol.
2.Cellular metabolism.
3. Synthesis of glycogen.
4. Storage and metabolism of calcium.
5. Carbohydrate metabolism.
6. Catabolism and detoxification of toxic substances.
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Endoplasmic reticulum :structure and functions
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