Figure 12-5

   Topological relationships between compartments of the secretory and endocytic pathways in a eucaryotic cell

Topologically equivalent spaces are shown in red. In principle, cycles of membrane budding and fusion permit the lumen of any of these organelles to communicate with any other and with the cell exterior by means of transport vesicles. Blue arrows indicate the extensive network of outbound and inbound traffic routes, which we discuss in Chapter 13. Some organelles, most notably mitochondria and (in plant cells) plastids do not take part in this communication and are isolated from the traffic between organelles shown here.