1- Endoplasmic Reticulum:
The electron microscope reveals a complex network of channels, the endoplasmic reticulum (ER) which extends from plasma membrane to the nuclear membrane. It is an elaborate. tube like system of lipoprotein. There are two types of endoplasmic reticulum: (a) Agranulated or smooth endiplasmic reticulum (SER) and (b) Rough or granulated endoplasmic reticulum (RER). Smooth endoplasmic reticulum is not associated with ribosomes. It is found in steroid producing cells like adipose cells (fat cells), interstitial cells, glycogen storing cells (liver) and the muscle cells. Rough or granular endoplasmic reticulum, is heavily coated with ribosomes on its outer surface towards cytoplasmic surface. Rough ER, occurs mostly in protein synthesising cells. Such as those of the mammalian salivary glands and pancreas. Although most cells contain both rough and smooth ER but they vary from cell to cell.
The endoplasmic reticulum has many important functions. Primarily, it serves as a supporting platform for the ribosomes. The ER forms a structural framework of the cell with increased surface for various metabolic reactions, and they themselves take an active part by means of attached enzymes.
2- Mitochondria
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