The cytoskeleton, mitochondrial
bioenergetics and apoptosis
Professor Daniel C. Hoessli
March 2013
The red cell cytoskeleton
The red cells (erythrocytes) contain a cytoskeleton
which is integrated in the plasma membrane,
conferring to the red cell its biconcave shape.
The red cell is extremely resilient and made to
resist the very strong shear forces of the blood
circulation.
Figure 11-30 Essential Cell Biology (© Garland Science 2010)
The major protein of the red cell cytoskeleton is spectrin, which is tethered to
two membrane proteins:
1) Glycophorin, its main attachment point, where spectrin ends contact the cytoskeletal
proteins actin and tropomyosin
2) Band 3, where the red cell specific protein ankyrin anchors band 3 to the side of
spectrin filaments
Figure 11-31 Essential Cell Biology (© Garland Science 2010)
The cytoskeleton of nucleated cells
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The cytoplasm is structured and organized by 3
different polymeric filamentous structures, the
cytoskeleton.
All cells contain actin filaments, intermediate
filaments and microtubules.
Movement of organelles and intracellular
macromolecules occurs along microtubules,
and is powered by motor proteins (kinesins and
dyneins).
Cytoskeleton of nucleated cells
This is the typical arrangement in nucleated cells,
showing the actin cytoskeleton in red and the microtubules in green.
The two types of filaments coincide in membrane
protrusions (yellow).
The nucleus appears in blue and microtubules
radiate from the nucleus, while the actin filaments
are peripherally disposed, without connections
with the nucleus.
Figure 17-1 Essential Cell Biology (© Garland Science 2010)
The dynamic and the structural
components of the cytoskeleton
The microtubules (MT) are highly dynamic. The MT
networks are constantly modified: MT are shortened or
elongated. They organize the cyoplasmic space.
The actin filaments (or microfilaments, MF) are highly
dynamic as well and power the cellular movements.
The intermediate filaments (IF) are purely structural and
provide epithelial sheets with resilient properties. In
epithelial cells, IF consist of keratin and connect the
cells in the sheet. In mesenchymal cells (i.e.
lymphocytes), IF consist of another protein, vimentin,
which is devoid of connecting properties
Figure 17-18a Essential Cell Biology (© Garland Science 2010)
Figure 17-18b, c Essential Cell Biology (© Garland Science 2010)
Figure 17-9 Essential Cell Biology (© Garland Science 2010)
Microtubules originate
from the centrosome
Figure 17-8a Essential Cell Biology (© Garland Science 2010)
Figure 17-8b Essential Cell Biology (© Garland Science 2010)
Actin filaments make the
backbone of cilia and
Other membrane protrusions
Figure 17-8c Essential Cell Biology (© Garland Science 2010)
Figure 17-10a, b Essential Cell Biology (© Garland Science 2010)
Figure 17-10c Essential Cell Biology (© Garland Science 2010)
How to move along microtubules ?
A variety of motor proteins can move along MTs.
The two main categories of moto proteins are:
The kinesins, and
The dyneins
Different dyneins and different kinesins have
distinct tails that accomodate different
„cargoes“.
Dyneins and kinesins move in opposite directions
on the polarized microtubule
Figure 17-14 Essential Cell Biology (© Garland Science 2010)
Figure 17-16 Essential Cell Biology (© Garland Science 2010)
Figure 17-17 Essential Cell Biology (© Garland Science 2010)
Figure 17-32 Essential Cell Biology (© Garland Science 2010)
Figure 17-33a, b Essential Cell Biology (© Garland Science 2010)
Figure 17-33c Essential Cell Biology (© Garland Science 2010)
Figure 17-28 Essential Cell Biology (© Garland Science 2010)
Figure 17-30 Essential Cell Biology (© Garland Science 2010)
Figure 17-37 Essential Cell Biology (© Garland Science 2010)
Figure 16-14 Essential Cell Biology (© Garland Science 2010)
Figure 17-3f Essential Cell Biology (© Garland Science 2010)
Figure 17-4 Essential Cell Biology (© Garland Science 2010)
Figure 17-3 Essential Cell Biology (© Garland Science 2010)
Figure 17-5 Essential Cell Biology (© Garland Science 2010)
Figure 17-7a Essential Cell Biology (© Garland Science 2010)
Figure 17-2b Essential Cell Biology (© Garland Science 2010)
Table 17-1 Essential Cell Biology (© Garland Science 2010)
Plectin (green) in a connecting protein that joins MT (actin filaments have been removed)
Figure 17-6 Essential Cell Biology (© Garland Science 2010)
Epithelial cells utilize IF and MF as
structural components
IF (keratin) constitute large bundles of filaments
that run through the entire cell and connect the
cell with the next one at the desmosomes and
hemidesmosomes.
MF in form of filamentous actin belts, also run
through the cell from one adherens junction to
the other junction. These belts allow anchoring
of other MF bundles that run at 90° into
microvilli.
Figure 20-22 Essential Cell Biology (© Garland Science 2010)
Figure 20-27 Essential Cell Biology (© Garland Science 2010)
Figure 20-25 Essential Cell Biology (© Garland Science 2010)
Summary
The cytoskeletal organization of a cell differs
between strongly associated cells (epithelial,
nerve cells) and individual ones (mesenchymal).
The structural role of tubules and filaments is
essential in epithelial cells (intercellular
adhesion) and the functional cytoskeleton
supports mesenchymal cells' various functions
(movement and phagocytosis).
In all cells, the MT network is needed for internal
organization, cell division and movement of
organelles and smaller objects.