Cytoskeleton • Figure 3.3
Filaments and tubules of the cytoskel-
eton give the cell shape and generate
movement.
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g? tf t ‘ r r
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c. Microtubule
Functions of the Cytoskeleton
1. Serves as a scaffold that helps to determine a cell’s shape
and to organize the cellular contents.
2. Aids movement of organelles within the cell, of chromosomes
during cell division, and of whole cells such as phagocytes.
The Cytoplasm Contains
Many Organelles
The cytoplasm is the region between the plasma mem-
brane and the nucleus. It consists of the intracellular fluid
called cytosol and organelles. Cytosol consists of water
plus dissolved ions, proteins, amino acids, fatty acids, ATP,
and gases. The organelles are membrane-bound compart-
ments where specialized functions happen. An overview of
the cell’s organelles is provided in Figure 3.1, and here we
will take a closer look at many of them.
For a long time, biologists thought that cells were
like bags containing water and organelles. However, cells
actually have an internal “skeleton” that gives them spe-
cific shapes.
Cytoskeleton
The cytoskeleton is made of networks
of the following protein elements (Figure 3.3):
Microfilaments
(mi-kro-FIL-a-mentz)—Small protein
strands that provide mechanical
support and generate force for
movement. They are analogous
to muscles in your body. They
also anchor proteins within the
plasma membrane and provide
support for microvilli.
Intermediate
filaments—Protein
strands
that
are
larger
than
microfilaments
but
smaller
than
microtubules. They hold organelles in place and attach
cells to one another.
Microtubules
(mi-kro-TOO-bul'z)—Long,
hollow
protein tubes that determine shape and movement
similar to the way bones shape your body. They are also
the stiff components of cilia and flagella.
Centrosomes
Centrosomes (SEN-tro-somz) are located
near the nucleus. They consist of a pair of centrioles and
pericentriolar material. Centrioles (SEN-tre-olz) are hol-
low cylinders, each made of nine sets of three microtubules.
They are surrounded by proteins called tubulins, which make
up the pericentriolar material (Figure 3.4). As you will see
later in the chapter, centrosomes play a role in cell division.
microvilli
Micro-
scopic finger-like pro-
jections of the plasma
membrane in some
cells that increase the
surface area of the cell
for absorption.
Centrosomes • Figure 3.4
Centrosomes consist of a pair of centrioles and pericentriolar
material and play a role in cell division.
Centrioles
Microtubule
triplets
Pericentriolar material
Function of the Centrosome
The pericentriolar material of the centrosome contains
tubulins that build microtubules in nondividing cells
and form the mitotic spindle during cell division.
Cells Have Distinct Parts
53
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