Rough endoplasmic reticulum with ribosomes on the surface (mammal neuron, CNS), coloured transmission electron micrograph (TEM). The endoplasmic reticulum (ER) is a network of membranous tubules within the cytoplasm of eukaryotic cells. Part of the ER is continuous with the nuclear membrane and is prominent component of the cell cytoplasm. It usually has ribosomes attached and is involved in protein and lipid synthesis. There are two types of ER: rough endoplasmic reticulum (rough ER) and smooth endoplasmic reticulum (smooth ER). Both types are present in plant and animal cells. The two types of ER often appear as if separate, but they are sub-compartments of the same organelle. Cells specialising in the production of proteins will tend to have a larger amount of rough ER whilst cells producing lipids (fats) and steroid hormones will have a greater amount of smooth ER. Magnification: x12,510 when shortest axis printed at 25 millimetres.
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