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Eukaryotic Membranes: Plastids
and Vacuoles
• Vacuoles are single
membrane sacs that
separate some
substance from the
cytosol.
Eukaryotic Membranes: Plastids
and Vacuoles
• Vacuoles have varied functions
– Central vacuole in plants is for support and
storage of metabolic wastes
– there are food storage vacuoles
– there are waste storage vacuoles
Eukaryotic Membranes:
Cytoskeleton
• Organelles do not
drift about the
cytoplasm
haphazardly, rather
they are attached to
a network of protein
fibers called the
cytoskeleton
Eukaryotic Membranes:
Cytoskeleton
• Parts of complex
metabolic pathways
may be fastened in
sequence to the
cytoskeleton so that
molecules pass from
one enzyme to the
next.
Eukaryotic Membranes:
Cytoskeleton
•
The cytoskeleton is constructed of:
1. Microfilaments (thin)
2. Intermediate filaments (medium)
3. Microtubules (thick)
Eukaryotic Membranes:
Cytoskeleton
•
The cytoskeleton performs the
following important functions:
1. Cell shape – without cell walls, the
cytoskeleton, especially networks of
intermediate filaments, determines the
shape of the cell
Eukaryotic Membranes:
Cytoskeleton
2. Cell movement – the assembly,
disassembly, and sliding of
microfilaments and microtubules causes
cell movement. Cell movement includes
both the familiar “crawling” of amoebae
and white blood cells and the migration
and shape changes that occur during the
development of multicellular organisms.
Eukaryotic Membranes:
Cytoskeleton
3. Organelle Movement – Microtubules and
microfilaments move organelles from place to
place within a cell. For example, microfilaments
attach to vesicles formed during endocytosis,
when large particles are engulfed by the plasma
membrane and pull the vesicles into the cell.
Vesicles budded off the ER and Golgi complex
are probably guided by the cytoskeleton as well.
Eukaryotic Membranes:
Cytoskeleton
4. Cell division – microtubules and microfilaments
are essential to cell division in eukaryotic cells.
First, when eukaryotic nuclei divide, microtubules
move the chormosomes into the daughter nuclei.
Second, in animal cells, division of the cytoplasm
of a single parent cell into two daughter cells
results from the contraction of a ring of
microfilaments that pinch the “waist” of the parent
c ell around the middle.
Eukaryotic Membranes: Flagella
and Cillia
• Cilia and flagella are slender extensions
of the plasma membrane.
– Each contains a ring of nine fused pairs of
microtublules in the center of a ring
arrangement.
– The main difference in these two is the
number, length, and direction of force.
Eukaryotic Membranes: Flagella
and Cillia
• Cilia – are short and
numerous. They
provide force in a
direction parallel to
the plasma
membrane. “oars”
Eukaryotic Membranes: Flagella
and Cillia
• Flagella are long,
not numerous, and
provide forse
perpendicular to the
plasma membrane.
“motorboat”
Eukaryotic Membranes:
Centrioles
• Centrioles are short,
barrel-shaped rings
of microtubules.
• Their function will be
discussed later