Cell Structure and Function
vary both in size and shape and in the appearance of their
, yet they are generally the easiest organelles to
transmission electron micrographs. The striking features are the
, which are inwardly
directed extensions of the inner mitochondrial membrane. The
typically consists of ﬂ
attened, membrane-delimited sacs. The
distinguishing feature of RER is the presence of ribosomes (polyribosomes) attached to the outer surface of the membrane.
also consists of membrane-delimited spaces, but these are usually in the form of a labyrinth of branching tubules. The surface of
the membrane of SER is smooth, with no attached ribosomes.
are composed of stacks of ﬂ
delimited sacs along with associated vesicles. Shapes of the sacs can vary, but often they are bowl shaped, so that there is a convex
face (the forming face) and a concave face (the maturing face).