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Endoplasmic Reticulum: Structure, Types and Function of Endoplasmic Reticulum!
The electron microscope reveals an extensive membrane system in the cytoplasm called Endoplasmic reticulum (ER).
It was first reported by Porter in 1945. This continuous membrane system connects the nuclear membrane on one end and the cell membrane on the other.
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All cells do not have Endoplasmic reticulum. It is generally absent in egg and embryonic cells. Generally, ELECTRONS is fully developed in cells actively engaged in protein and hormone synthesis. Endoplasmic Reticulum contains three different types of structure.
These are cisternae, vesicles and tubeless:
(a) Cisternae:
These are long, flat and un-branched plates or lamellae arranged in parallel rows.
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(b) Vesicles:
They are usually round or ovoid sacs. They often occur isolated in the cytoplasm.
(c) Tubules:
They are irregularly branched tube-like structures having a diameter of 50-100n. These are surrounded by this unit membrane of 50-60 thickness and their lumen is filled with the secretary products of the cell.
There are two types of ER, such as smooth walled and rough walled.
They may be present in the same or different types of cells namely:
(i) Smooth Endoplasmic Reticulum (SEE):
The surface of this type of reticulum is smooth as ribosome’s not attached to it. Smooth ER is actively engaged in steroid synthesis, carbohydrate metabolism, pigment production etc. in cells, (u) Rough Endoplasmic Reticulum: The rough ER have ribosome attached throughout the surface. These are present in cells, which are active in protein synthesis.
The major functions these are the following:
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(a)Common to both Endoplasmic Reticulum:
(i) Forms the skeletal framework.
(ii) Active transport of cellular materials.
(iii) Metabolic activities due to presence of different enzymes.
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(iv) Provides increased surface area for cellular reactions.
(v) Formation of nuclear membrane during cell division.
(b) Function of Smooth Endoplasmic Reticulum:
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(i) Lipid synthesis.
(ii) Glycogen synthesis.
(iii) Steroid synthesis like cholesterol, progesterone, testosterone, etc.
(iv) Metabolism of carbohydrates .
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(v) Detoxification function.
(vi) Major storage and released site of inter cellular calcium ions.
(c) Function of Rough Endoplasmic Reticulum:
(i) It provides site for protein synthesis.
(ii) Protein translocation, folding and transport of protein.
(iii) Glycosylation (this is the relation of a saccharides group with a hydroxyl or amino functional group to form a glucoside).
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(iv) Disulfide bond formation (disulfide bonds stabilize the tertiary and quaternary structures of many proteins).
(v) Membrane synthesis.
