92
UNIT 1
Organization of the Body
3
with ribosomes on its external face. Te inner nuclear mem-
brane is lined by the
nuclear lamina
, a network of
lamins
(rod-
shaped proteins that assemble to form intermediate filaments)
that maintains the shape of the nucleus and acts as a scaffold to
organize DNA in the nucleus (Figure 3.29b, bottom).
The Nuclear Envelope
Te nucleus is bounded by the
nuclear envelope
, a
double
membrane barrier separated by a fluid-filled space (similar to
the mitochondrial membrane). Te outer nuclear membrane is
continuous with the rough ER of the cytoplasm and is studded
Chromatin (condensed)
Nuclear envelope
Nucleus
Nuclear
pores
Fracture
line of outer
membrane
Nuclear pore complexes.
Each pore is ringed
by protein particles.
Surface of nuclear envelope.
Nuclear lamina.
The netlike lamina
composed of intermediate filaments formed by
lamins lines the inner surface of the nuclear
envelope.
Nucleolus
Cisterns of rough ER
(a)
(b)
Figure 3.29
The nucleus.
(a)
Three-dimensional diagram of the nucleus, showing the continuity
of its double membrane with the ER.
(b)
Freeze-fracture transmission electron micrographs (TEMs).
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