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|Chapter Three: Cell Structures|
Cells can easily move and alter their shape because they possess a network of fibers called the cytoskeleton. The cytoskeleton attaches to the cell membrane and to most of the organelles. As the contents of the cell move around by cyclosis, the fibers of the cytoskeleton can break and reassemble to keep the cytoskeleton functional. The cytoskeleton consists of four types of fibers, all of which are made of protein. These fibers are microtubules, intermediate filaments, microfilaments, and microtrabeculae.
Microtubules are about 20 to 25 nanometers in diameter and usually extend from the center of the cell to the cell membrane. Microtubules are involved cell reproduction, and they also are important elements in specialized structures for cell movement called cilia and flagella.
Intermediate filaments have a diameter of 7 to 10 nanometers. Intermediate filaments are formed from a protein structure called fibrous protein which cannot be as easily disassembled as either the microtubules or the microfilaments can. They have a strong, ropelike structure which helps to give the cell strength and to maintain its shape.
Microfilaments, which are only 3 to 6 nanometers in diameter, consist of a protein called actin. Unlike microtubules which are components of structures designed to move the cell around, microfilaments are used to aid in movement in cells without such specialized structures.
The microtrabeculae are tiny fibers which interconnect all of the structures within the cell. Biologists believe that, like the intermediate fibers, the microtrabeculae help to give the cell shape. At the intersections of the microtrabeculae fibers are ribosomes.