1. The eukaryotic cytoplasm has a set of long, thin fibers called the cytoskeleton, which plays three important roles in cellular structure and function: 1. Maintains cell shape and support. 2. Provides for various types of cell movement. 3. Helps move things within the cell. Figure 4.21 The Cytoskeleton

2. Three important components of the cytoskeleton are: Microfilaments Intermediate filaments Microtubules Figure 4.21 The Cytoskeleton

3. Microfilaments are made up of strands of the protein actin. Actin monomer They have two major roles: 1. They help the cell or parts of the cell to move. 2. They stabilize cell shape. Figure 4.21 The Cytoskeleton

4. Intermediate filaments are made up of fibrous proteins that are organized into tough, ropelike assemblages. They have two major structural functions: 1.They stabilize cell structure. 2.They resist tension. Fibrous subunit Figure 4.21 The Cytoskeleton

5. Microtubules are long, hollow cylinders made up of many molecules of the protein tubulin. Tubulin consists of two subunits:  -tubulin and  -tubulin.  Tubulin dimer  -Tubulin monomer  -Tubulin monomer Microtubules have two roles: 1.They form a rigid internal skeleton. 2.They act as a framework along which motor proteins can move structures in the cell. - End + Figure 4.21 The Cytoskeleton