What you will learn
What do you get if you take some tubing, and make the tubes smaller and smaller and smaller? You get very small tubes, or microtubes. Very small tubes, or microtubules, together with microfilaments, form the basis of the “skeleton” inside the cell.
The cytoplasm consists of everything inside the cell membrane of the cell, excluding the nucleus in a eukaryotic cell. It includes the watery, gel-like material called cytosol, as well as various structures. The water in the cytoplasm makes up about two-thirds of the cell’s weight and gives the cell many of its properties.
The cytoplasm has several important functions, including:
The cytoskeleton is a cellular “scaffolding” or “skeleton” that crisscrosses the cytoplasm. All eukaryotic cells have a cytoskeleton, and recent research has shown that prokaryotic cells also have a cytoskeleton. The eukaryotic cytoskeleton is made up of a network of long, thin protein fibers and has many functions. It helps to maintain cell shape. It holds organelles in place, and for some cells, it enables cell movement. The cytoskeleton also plays important roles in both the intracellular movement of substances and in cell division. Certain proteins act like a path that vesicles and organelles move along within the cell. The threadlike proteins that make up the cytoskeleton continually rebuild to adapt to the cell’s constantly changing needs. Three main kinds of cytoskeleton fibers are microtubules, intermediate filaments, and microfilaments.
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The eukaryotic cytoskeleton. (Left) Microfilaments are shown in red, microtubules in green, and the nuclei are in blue. By linking regions of the cell together, the cytoskeleton helps support the shape of the cell. |
Microtubules | Intermediate Filaments | Microfilaments | |
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Fiber Diameter | About 25 nm | 8 to 11 nm | Around 7 nm |
Protein Composition | Tubulin, with two subunits, alpha and beta tubulin | One of different types of proteins such as lamin, vimentin, and keratin | Actin |
Shape | Hollow cylinders made of two protein chains twisted around each other | Protein fiber coils twisted into each other | Two actin chains twisted around one another |
Main Functions | Organelle and vesicle movement; form mitotic spindles during cell reproduction; cell motility (in cilia and flagella) | Organize cell shape; positions organelles in cytoplasm structural support of the nuclear envelope and sarcomeres; involved in cell-to-cell and cell-to-matrix junctions | Keep cellular shape; allows movement of certain cells by forming cytoplasmatic extensions or contraction of actin fibers; involved in some cell-to-cell or cell-to-matrix junctions |
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Which of the following statement(s) are true about cytoskeleton fibers?
Microfilaments are made up of the protein actin.
Intermediate filaments are made up of a variety of proteins.
Microfilaments are involved in many cellular events that involve movement.
Cytoskeletal fibers are polymers of carbohydrates.