Essential Cell Biology 5th edition

CHAPTER SEVENTEEN
17
Cytoskeleton
The ability of eukaryotic cells to organize the many components in
their interior, adopt a variety of shapes, interact mechanically with the
environment, and carry out coordinated movements depends on the
cytoskeleton—an intricate network of protein filaments that extends
throughout the cytoplasm (Figure 17–1). This filamentous architecture
helps to support the large volume of cytoplasm, a function that is particularly
important in animal cells, which have no cell walls. Although some
cytoskeletal components are present in bacteria, the cytoskeleton is most
prominent in the large and structurally complex eukaryotic cell.
INTERMEDIATE FILAMENTS
MICROTUBULES
ACTIN FILAMENTS
MUSCLE CONTRACTION
Unlike our own bony skeleton, however, the cytoskeleton is a highly
dynamic structure that is continuously reorganized as a cell changes
shape, divides, and responds to its environment. The cytoskeleton is not
only the “bones” of a cell but its “muscles” too, and it is directly responsible
for large-scale movements, including the crawling of cells along a
surface, the contraction of muscle cells, and the changes in cell shape
that take place as an embryo develops. Without the cytoskeleton, wounds
would never heal, muscles would not contract, and sperm would never
reach the egg.
While the interior of the eukaryotic cell is dynamic, it is also highly organized,
with organelles that carry out specialized functions concentrated in
different areas and linked by transport systems (discussed in Chapter 15).
It is the cytoskeleton that controls the location of the organelles and provides
the machinery for transport between them. A cytoskeletal machine
is also responsible for the segregation of chromosomes into two daughter
cells at cell division and for pinching apart those two new cells, as we
discuss in Chapter 18.