It was discovered by Porter (1945) and Thompson (1945). The name was given by Porter in 1953. Endoplasmic reticulum is a 3-dimensional, complicated and interconnected system of membrane-lined channels that run through the cytoplasm. The endoplasmic reticulum is found in all eukaryotic cells except the R.B.Cs of mammals. eggs and embryonic cells. In adipose tissue it is poorly developed. It is extensively developed in the cells which are actively engaged in metabolic activities and protein synthesis e.g. liver cells, cells of pancreas etc.
Types:- Depending upon the nature of its membrane, endoplasmic reticulum is of two types, smooth and rough. Endoplasmic reticulum may develop from pre-existing E.R, plasmalemma or nuclear envelop.
Smooth Endoplasmic Reticulum:- It has a smooth membrane which do not bear ribosomes. It is, therfore, also called agranular endoplasmic reticulum. This type of ER is found in cells engaged in the synthesis and storage of glycogen e.g. glycogen storing liver cells, adipose cells, interstitial cells etc. Sphaerosomes are believed to originated from SER.
Rough Endoplasmic Reticulum:- This type of ER bears ribosomes attached to the outer surface of its membrane. RER is, therfore, also called granular endoplasmic reticulum. On account of the presence of ribosomes, the RER engaged in the protein synthesis and secretory activity e.g. plasma cells, pancreatic acinus cells etc.
Structure:- Endoplasmic reticulum consists of membrane lined channels or spaces. The channels contain a fluid called endoplasmic matrix. Endoplasmic reticulum can exist in three forms- Cisternae, Vesicles and Tubules.
Cisternae:- They are flat interconnected sac-like parts of ER which are 40-50 nm in diameter. The cisternae are found in bundles. They occur in the cells actively involved in synthetic activity.
Vesicles:- They are oval and round sacs of 25-500 nm in diameter. They remain isolated in the cytoplasm. The vesicles are also called microsomes.
Tubules:- They are tube like extensions which may be connected with cisternae or vesicles to form a reticular system. The tubules can be regular or irregular with diameter of 50-100nm.
Functions:-
i) It provides a large surface inside the cell for various physiological activities.
ii) It functions as cytoskeleton by providing mechanical support to cytoplasmic matrix.
iii) Endoplasmic reticulum keeps the various organelles in their position.
iv) Endoplasmis reticulum controls the movement of materials between two adjecent protoplast through plasmodesmata.
v) It provide membranes to nuclear envelop after telophase.
vi) The membranes of ER contains large number of enzymes.
Functions of Rough Endoplasmic Reticulum:-
i) RER provides a large surface area to ribosomes.
ii) It bears enzymes in the region of pores for modifying polypeptides synthesised by attached ribosomes.e.g. glycosylation.
iii) It provides enzymes precursors for the formation of lysosomes by Golgi Complex.
Types:- Depending upon the nature of its membrane, endoplasmic reticulum is of two types, smooth and rough. Endoplasmic reticulum may develop from pre-existing E.R, plasmalemma or nuclear envelop.
Smooth Endoplasmic Reticulum:- It has a smooth membrane which do not bear ribosomes. It is, therfore, also called agranular endoplasmic reticulum. This type of ER is found in cells engaged in the synthesis and storage of glycogen e.g. glycogen storing liver cells, adipose cells, interstitial cells etc. Sphaerosomes are believed to originated from SER.
Rough Endoplasmic Reticulum:- This type of ER bears ribosomes attached to the outer surface of its membrane. RER is, therfore, also called granular endoplasmic reticulum. On account of the presence of ribosomes, the RER engaged in the protein synthesis and secretory activity e.g. plasma cells, pancreatic acinus cells etc.
Structure:- Endoplasmic reticulum consists of membrane lined channels or spaces. The channels contain a fluid called endoplasmic matrix. Endoplasmic reticulum can exist in three forms- Cisternae, Vesicles and Tubules.
Cisternae:- They are flat interconnected sac-like parts of ER which are 40-50 nm in diameter. The cisternae are found in bundles. They occur in the cells actively involved in synthetic activity.
Vesicles:- They are oval and round sacs of 25-500 nm in diameter. They remain isolated in the cytoplasm. The vesicles are also called microsomes.
Tubules:- They are tube like extensions which may be connected with cisternae or vesicles to form a reticular system. The tubules can be regular or irregular with diameter of 50-100nm.
Functions:-
i) It provides a large surface inside the cell for various physiological activities.
ii) It functions as cytoskeleton by providing mechanical support to cytoplasmic matrix.
iii) Endoplasmic reticulum keeps the various organelles in their position.
iv) Endoplasmis reticulum controls the movement of materials between two adjecent protoplast through plasmodesmata.
v) It provide membranes to nuclear envelop after telophase.
vi) The membranes of ER contains large number of enzymes.
Functions of Rough Endoplasmic Reticulum:-
i) RER provides a large surface area to ribosomes.
ii) It bears enzymes in the region of pores for modifying polypeptides synthesised by attached ribosomes.e.g. glycosylation.
iii) It provides enzymes precursors for the formation of lysosomes by Golgi Complex.
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