Insidetheendoplasmicreticulum

The endoplasmic reticulum (ER) is a continuous network of flattened sacs, tubules, and associated vesicles that stretches throughout the eukaryotic cell's cytoplasm.

- TAPAN KUMAR MAITRA

Although the name sounds formidable, it is actually quite descriptive. Endoplasmic simply means 'within the plasm' (of the cell), and reticulum is a Latin word meaning 'network.' The sacs are called ER cisternae (singular: ER cisterna), and the space enclosed by the sacs and tubules is called the ER lumen. Of a typical mammalian cell's total complement of membrane, 50-90 per cent is devoted to surrounding the ER lumen.

Unlike more prominent organelles, such as the mitochondrion or chloroplast, however, the ER is not visible by light microscopy unless one or more of its components are stained with a dye or labeled with a fluorescent molecule.

The ER was first observed in the late nineteenth century, when it was noted that some eukaryotic cells, particularly those involved in secretion, contained regions that stained intensely with basic dyes. These regions were called ergastoplasm, but their significance remained in doubt until the 1950s, which saw an enormous increase in resolving power provided by electron microscopy. This development allowed cell biologists to visualise for the first time the ER's elaborate network of intracellular membranes and to investigate the role of the ER in cellular processes. More recently, research in microchip technology and proteomics—the in vitro study of cellular protein-protein interactions—has further clarified our understanding of ER structure and function.