Eukaryotic cells contain a plurality of organelles distinguished by
their specific membranes and contents. Their biogenesis occurs by growth
and division of preexisting structures rather than de novo. Mitochondria
and chloroplasts, which appear to be descended from prokaryotic
ancestors, have retained some DNA and the biosynthetic capability for
its expression. They synthesize, however, only a few of their proteins
themselves. Most of their proteins are synthesized on free ribosomes in
the cytoplasm and are only assembled in the correct membrane after
synthesis is complete. The biogenesis of peroxisomes and glyoxysomes
also appears to occur by an incorporation of proteins synthesized first
in the cytoplasm. Other organelles, the Golgi complex, lysosomes,
secretory vesicles, and the plasma membrane, are formed in a different
manner. Their proteins are assembled in the membrane of the endoplasmic
reticulum during trans- lation by bound ribosomes and they must then be
transported to the correct membrane. The 1980 Mosbach Colloquium was one
of the first attempts to discuss the biogenesis of the various
organelles in biochemical terms. This was appropriate since the crucial
problems now center on the search for signals and receptors that dictate
the site of assembly, the route taken, and the final location of a
particular organelle protein. The assembly of prokaryotic membranes and
the membrane of an animal virus were also discussed, since these simpler
systems might shed light on the biogenesis of organelles in eukaryotes.