Figure 227

Electron micrograph of COP-I- and COP-II-coated vesicles, a. This image shows COP-l-coated vesicles that initiate retrograde transport from the c/s-Golgi network to the rER. In this image, taken of a quick-freeze deep-etch preparations, note the structure of the c/s-Golgi network and emerging vesicles, x27,000. b. Image of COP-II-coated vesicles that are responsible for anterograde transport. Note that the surface coat of these vesicles is different from that of clathrin-coated vesicles, x 50,000. (Courtesy of Dr. John E. Heuser, Washington University School of Medicine.)

In this case, the ribosomes and polysomes are "free" in the cytoplasm; i.e., they are not attached to membranes of the endoplasmic reticulum. The large basophilic bodies of nerve cells, called Nissl bodies, consist of both rER and large numbers of free ribosomes (Fig. 2.28). All ribosomes rSsgxk «fee ...#

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