With and Without the

1
With and Without the Cell Cytoskeleton
ANAT3231 Cell Biology Dr. Mark Hill Research 2004
Demir, T., Deng, L.R., Feng, S Ghaly, S., and
Saekang, E.

• Introduction
• The cytoskeleton is responsible for the
  organisation of the organelles inside a cell. It
  is the bulk of the cell and assists with cell
  motility, mitosis and meiosis, and maintaining
  the shape and stability of the cell. The
  cytoskeleton is made up of long fibres of
  polymers and subunits that form into one of the
  following
• Microtubules
• Intermediate Filaments
• Microfilaments

Figure 1 General arrangement of cytoskeletal
filaments in a typical cell.1
Microfilaments Microfilaments are left-handed
helices formed by two-strands of F-actin
(fibrinous-actin) polymers.12 These are composed
of rough spherical G-actin (globular-actin)
monomers.12 They are the thinnest of the three
cytoskeleton filaments and are about 8nm in
diameter.12 The bulk of these filaments are
anchored to the cytoplasmic side of cell plasma
membranes and its nearby structures.12 The rest
is evenly distributed throughout the
cell.12 FUNCTIONS The meshwork of
microfilaments provide the cell mechanical
strength to support its plasma membrane and aids
in cell motility.5 It links transmembrane
proteins to allow communication between cells.5
It is also important in cell division, anchoring
centrosomes during prophase and acts in
cytokinesis.5 MALFUNCTIONS Because the
interactions of microfilaments with proteins
involved in focal adhesions, structural and
functional perturbations of microfilaments have
been indicated as a feature in malignant
cancers.15 Malignant cells display features of
focal adhesion abnormalities and uncontrolled
cellular migration. 15 Thus the microfilament
network has been hugely implicated as a target
for cancer therapeutics.15
Microtubules Microtubules are long, straight,
hollow and rigid cylinders of about 25nm in
diameter.5 They are constructed of alternating
identical subunits of alpha and beta protein
tubulin, forming a protofilament.5 Its walls are
made up of 13 protofilaments which correlate with
one another laterally and the filament is able to
increase or decrease in length by adding or
removing proteins.5-6 They are seen in bundles
and found in the cytoplasm of all eukaryotic
cells, emanating from the center of an interphase
cell.5-6 FUNCTIONS Microtubules are the
drivers in cell motility. Dynamic instability of
the building blocks allows the tube to break down
and reform almost spontaneously.8 The alpha and
beta dimers combine to become the components of
cilia or the flagella.8 They are responsible for
transportation of vesicles from one organelle to
another.9 Most important in mitosis and meiosis,
where they form the bipolar poles in the cell
during interphase and allow for attachments,
splitting and pairing of chromosomes.9 MALF
UNCTIONS Occur during the formation of mitotic
spindles and chromosome segregation, which can
lead to disorders such as Klinefelter, Turner,
Down Syndromes, and tumour growth. 11 Taxol
polymerisation stops the treadmill motion of the
microtubules and inhibiting polymers from
advancing to anaphase.11 Taxol therefore, is an
important form of antimitotic drug used in
chemotherapies to treat cancers.8
Figure 5 Schematic diagram of a microfilament.13
Figure 3 Schematic view of a microtubule,
composed of alpha and beta proteins and linked in
13 linear sequences called protofilaments.7
Figure 6 In a cell, microfilaments (green)
interact with other proteins to form focal
adhesions (yellow) are structures important for
anchoring the cell as well as in cell-cell
interactions. 14
Figure 4 Green - Microtubules Blue - Daughter
chromosomes Red Mitochondria 10 (Michael W.
Davidson 2004)

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