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Endoplasmic Reticulum

These images show the distribution of the endoplasmic reticulum in cultured epithelial cells. The eukaryotic cell contains extensive internal membrane systems, such as the endoplasmic reticulum (ER) and the Golgi apparatus. A eukaryotic cells has two types of ER, rough and smooth. Rough ER (RER) plays a central role in the biosynthesis of proteins and lipids. It is a set of interconnected membranous sacs, canals, and saccules that define a single lumen. The rough is added due to the fact that the membrane is embedded with ribosomes. RER is prominent in cells with high secretory activity, such as plasma cells which synthesize antibodies.

A fluorescently stained image of the endoplasmic reticulum (green).

Endoplasmic Reticulum

The second type of ER, is smooth ER (SER). SER is abundant in cells that are involved in lipid metabolism. Cells that synthesize steroid hormones from cholesterol have an expanded SER to accommodate enzymes that make cholesterol and convert it into hormones.

Once a protein synthesized on a membrane-bound ribosome, it passes across the membrane of ER where the protein is processed by enzymes and folded into its correct three-dimensional conformation. Following the ER, the protein enters the Golgi apparatus where it is further modified by the addition of polysaccharide chains and packaged into vesicles. The ultimate fate of the protein is to be secreted out of the cell via exocytosis of the vesicles. All cells were processed using a gluteraldehyde fixation with an ER specific dye, 3,3'-dihexyloxacarbocyanine iodide (DiOC6(3)).

For further information on the endoplasmic reticulum, click the images below.

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