Thursday, September 16, 2010
Endoplasmic Reticulum of the Cell
Thursday, September 16, 2010 by Faizan Bhatti
Endoplasmic reticulum (ER) is a complex, membrane bound labyrinth of flattered sheets, sacs and tubules that branches and spreads throughout the cytoplasm. The number and shape of endoplasmic reticulum may vary from one cell type to another, also in different physiological and developmental stages of the same cell type. The enclosed shapes called cisternae contain certain chemical substances that may vary from cell to cell. Endoplasmic reticulum has communication with the exterior, with the nuclear envelope as well as to the Golgi apparatus. Endoplasmic reticulum is continuous from the nuclear envelope to the plasma membrane in the form of a series of channels that help various material to circulate throughout the cytoplasm. It is also a storage unit for enzymes and other proteins and a point of attachment for ribosomes.
Types of endoplasmic reticulum: On the basis of appearances, endoplasmic reticulum is classified as:
(1) Rough or granular endoplasmic reticulum.
(2) Smooth or agranular endoplasmic reticulum.
(1) Rough or granular endoplasmic reticulum:
This is the type of endoplasmic reticulum that bears on its cytoplasmic face large number of small granular structures, the ribosomes. Due to the presence of these ribosomes endoplasmic reticulum gives rough appearance so named as rough or granular endoplasmic reticulum. Ribosomes present on ER help in protein synthesis that is then transported to different parts of the cell including Golgi bodies through cisternae.
(2) Smooth or agranular endoplasmic reticulum:
This is the type of endoplasmic reticulum without ribosomes. They have their own enzyme system and perform certain important functions.
Most cells contain both types of endoplasmic reticulum although relative proportion varies among cells.
Functions of Endoplasmic reticulum:
It plays an important role in the activity of cell. The functions are:
(1) Mechanical support: Due to flexible nature of plasma membrane and ability to extend into the cytoplasm, it has connections with nuclear envelope and Golgi apparatus which help to provide mechanical support to the cell.
(2) Transportation of material: As the endoplasmic reticulum has direct or indirect convection with the important organelles of the cell as well as with the cytoplasm and exterior, it acts as a transporter for the transportation of different material within the cell and from surrounding cells.
(3) Synthesis and transportation of proteins: The rough endoplasmic reticulum is involved in the synthesis and transportation of cellular proteins.
(4) Detoxificaiton of harmful substances: Smooth endoplasmic reticulum due to its own enzyme system metabolizes or destroys the toxic substances like steroids, carcinogens and toxins.
(5) Synthesis of lipids: Smooth endoplasmic reticulum synthesis different types of lipids that are used for the formation of plasma membrane and steroid hormones like testosterone and estrogens. Glycogen and glycolipids are also synthesized here.
(6) Site of new membranes: They are site for synthesis of proteins and lipids and are also considered to be primary site of new membranes.
(7) Storage of calcium ions: Smooth endoplasmic reticulum sores calcium ions in muscle cells which are required for muscle contraction.Tags: Biology , Zoology
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