Transmission electron micrograph of rough endoplasmic reticulum in a pancreatic cell of a bat, Myotis lucifugus. Rough endoplasmic reticulum consists of extended sheets of paired membranes, with the external surface of the membranes covered in ribosomes. In this picture the paired membranes appear in large whorls & the ribosomes as dark dots on the outer surface. Rough endoplasmic reticulum occurs in cells actively engaged in protein synthesis, like this one producing digestive enzymes. Protein synthesis occurs on the ribosomes. Further processing & transportation takes place in the lumen of the paired membranes. Magnification: x3900 at 35mm size.
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