Endoplasmic ReticulumThe endoplasmic reticulum is a membranous network that extends throughout the cell.It is continuous with the nuclear envelope and the plasma membrane.Rough Endoplasmic ReticulumThe rough appearance of rough endoplasmic reticulum is due to the presence of ribosomeson the membrane.The rough ER functions in protein synthesis, especially proteins that are to be secreted to outside the cell (example: hormones). Proteinsenter the lumen (interior) of the endoplasmic reticulum while being synthesized. In addition to protein synthesis, the rough endoplasmic reticulum also functions in the modification of newly formed proteins. For example, some enzymes may add carbohydrate chains forming glycoproteins. Molecular chaperonesare enzymes that function to fold the newly-synthesized proteins into their proper shape.Vesiclesare small sacs that pinch off the endoplasmic reticulum or Golgi apparatus (discussed below) and transport molecules to other parts of the cell.
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