Basic Principles of Cell Structure and Function
inner nuclear membranes
are readily identif
ed in electron micrographs iF there is
cation and a Favorable plane oF section. In some cells, the outer nuclear membrane is studded with ribosomes, and
the perinuclear cisternae are continuous with the cisternae oF
. In a cell that is actively synthesizing proteins, the
that can be identif ed in electron micrographs as interruptions in the double-membrane arrange-
ment oF the nuclear envelope. Some Face-on views oF nuclear pores can be seen in the
. It can be seen that the pores are not
simply openings, but rather each has a diaphragm. Chromatin that is highly condensed, or
, is much more electron
dense than chromatin that is accessible to transcription, or
. Clumps oF heterochromatin tend to be located adjacent to
the inner nuclear membrane, with gaps that correspond to sites oF nuclear pores.
appear similar to heterochromatin but can
usually be distinguished by a more complex substructure oF granular, f
brous, and nucleolar organizer components.
The nucleus and its components.