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Eucaryotic
Cells -
The
eucaryotic
cells
are
characterized
by
the
presence
of
a
multiplicity
of
unit
membrane
systems
which
are
structurally
and
topologically
distinct
from
the
cytoplasmic
membrane.
These
membrane
systems
enable
the
segregation
of
different
eucaryotic
cytoplasmic
functions
into
specialized
organelles.
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The
most
complex
internal
membrane
system
is
the
endoplasmic
reticulum
(ER)
which
consists
of
an
irregular
network
of
interconnected
membrane
delimited
channels
that
cover
most
of
the
interior
of
the
cell
and
is
in
direct
contact
with
two
other
components
namely
the
nucleus
and
the
cytoplasmic
ribosomes.
Part
of
the
endoplasmic
reticulum
surrounds
the
nucleus
to
form
the
nuclear
membrane.
In
other
regions,
the
surface
of
the
membrane
is
covered
with
ribosomes
where
protein
synthesis
occurs.
These
proteins
then
pass
through
the
endoplasmic
reticulum
channels
to
the
different
parts
of
the
cell
cytoplasm.
In
the
eucaryotic
cell,
the
genetic
material
is
stored
in
chromosomes
(within
the
Nucleus)
although
mitochondria
and
chloroplasts
also
contain
characteristic
DNA.
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The
chromosomes
are
distinct
thread
like
structures
mainly
containing
deoxyribonucleic
acid
(DNA)
and
basic
proteins
such
as
histones.
The
size
and
the
number
of
the
chromosome
vary
widely
with
different
organisms.
The
nucleus
also
contains
a
nucleolus
which
is
a5sociated
with
a
specific
chromosomal
region
kn9wn
as
the
nucleolar
organizer
and
is
presumed
to
be
involved
in
ribosomal
RNA
(r-RNA)
synthesis.
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