{"id":577,"date":"2018-05-03T17:46:58","date_gmt":"2018-05-03T17:46:58","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/chapter\/the-cytoskeleton\/"},"modified":"2018-06-27T14:50:46","modified_gmt":"2018-06-27T14:50:46","slug":"the-cytoskeleton","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/chapter\/the-cytoskeleton\/","title":{"raw":"The Cytoskeleton","rendered":"The Cytoskeleton"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\nBy the end of this section, you will be able to do the following:\r\n<ul>\r\n \t<li>Describe the cytoskeleton<\/li>\r\n \t<li>Compare the roles of microfilaments, intermediate filaments, and microtubules<\/li>\r\n \t<li>Compare and contrast cilia and flagella<\/li>\r\n \t<li>Summarize the differences among the components of prokaryotic cells, animal cells, and plant cells<\/li>\r\n<\/ul>\r\n<\/div>\r\nIf you were to remove all the organelles from a cell, would the plasma membrane and the cytoplasm be the only components left? No. Within the cytoplasm, there would still be ions and organic molecules, plus a network of protein fibers that help maintain the cell's shape, secure some organelles in specific positions, allow cytoplasm and vesicles to move within the cell, and enable cells within multicellular organisms to move. Collectively, scientists call this network of protein fibers the cytoskeleton. There are three types of fibers within the cytoskeleton: microfilaments, intermediate filaments, and microtubules (<a class=\"autogenerated-content\" href=\"#fig-ch04-05-01\">(Figure)<\/a>). Here, we will examine each.\r\n<div id=\"fig-ch04-05-01\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"275\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174645\/Figure_04_05_01.jpg\" alt=\"Microfilaments line the inside of the plasma membrane, whereas microfilaments radiate out from the center of the cell. Intermediate filaments form a network throughout the cell that holds organelles in place.\" width=\"275\" height=\"694\" \/> <strong>Figure 1. <\/strong>Microfilaments thicken the cortex around the cell's inner edge. Like rubber bands, they resist tension. There are microtubules in the cell's interior where they maintain their shape by resisting compressive forces. There are intermediate filaments throughout the cell that hold organelles in place.[\/caption]\r\n\r\n<\/div>\r\n<div id=\"fs-id1228137\" class=\"bc-section section\">\r\n<h3>Microfilaments<\/h3>\r\n<p id=\"fs-id1662602\">Of the three types of protein fibers in the cytoskeleton, microfilaments are the narrowest. They function in cellular movement, have a diameter of about 7 nm, and are comprised of two globular protein intertwined strands, which we call actin (<a class=\"autogenerated-content\" href=\"#fig-ch04-05-02\">(Figure)<\/a>). For this reason, we also call microfilaments actin filaments.<\/p>\r\n\r\n<div id=\"fig-ch04-05-02\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"275\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174648\/Figure_04_05_02.jpg\" alt=\"This illustration shows two actin filaments wound together. Each actin filament is composed of many actin subunits connected together to form a chain.\" width=\"275\" height=\"753\" \/> <strong>Figure 2. <\/strong>Two intertwined actin strands comprise microfilaments.[\/caption]\r\n\r\n<\/div>\r\nATP powers actin to assemble its filamentous form, which serves as a track for the movement of a motor protein we call myosin. This enables actin to engage in cellular events requiring motion, such as cell division in eukaryotic cells and cytoplasmic streaming, which is the cell cytoplasm's circular movement in plant cells. Actin and myosin are plentiful in muscle cells. When your actin and myosin filaments slide past each other, your muscles contract.\r\n<p id=\"fs-id1973921\">Microfilaments also provide some rigidity and shape to the cell. They can depolymerize (disassemble) and reform quickly, thus enabling a cell to change its shape and move. White blood cells (your body\u2019s infection-fighting cells) make good use of this ability. They can move to an infection site and phagocytize the pathogen.<\/p>\r\n\r\n<div id=\"fs-id1685480\" class=\"interactive textbox tryit\">\r\n<h3>Link to Learning<\/h3>\r\n<p id=\"fs-id1364358\">To see an example of a white blood cell in action, watch a short time-lapse <a href=\"https:\/\/youtu.be\/AUih856vaQY\">video<\/a> of the cell capturing two bacteria. It engulfs one and then moves on to the other.<\/p>\r\n\r\n<div id=\"eip-id3083425\"><\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-id1361987\" class=\"bc-section section\">\r\n<h3>Intermediate Filaments<\/h3>\r\n<p id=\"fs-id1358496\">Several strands of fibrous proteins that are wound together comprise intermediate filaments (<a class=\"autogenerated-content\" href=\"#fig-ch04-05-03\">(Figure)<\/a>). Cytoskeleton elements get their name from the fact that their diameter, 8 to 10 nm, is between those of microfilaments and microtubules.<\/p>\r\n\r\n<div id=\"fig-ch04-05-03\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"350\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174650\/Figure_04_05_03.jpg\" alt=\"This illustration shows 10 intermediate filament fibers bundled together.\" width=\"350\" height=\"116\" \/> <strong>Figure 3. <\/strong>Intermediate filaments consist of several intertwined strands of fibrous proteins.[\/caption]\r\n\r\n<\/div>\r\n<p id=\"fs-id1561464\">Intermediate filaments have no role in cell movement. Their function is purely structural. They bear tension, thus maintaining the cell's shape, and anchor the nucleus and other organelles in place. <a class=\"autogenerated-content\" href=\"#fig-ch04-05-01\">(Figure)<\/a> shows how intermediate filaments create a supportive scaffolding inside the cell.<\/p>\r\n<p id=\"fs-id1232860\">The intermediate filaments are the most diverse group of cytoskeletal elements. Several fibrous protein types are in the intermediate filaments. You are probably most familiar with keratin, the fibrous protein that strengthens your hair, nails, and the skin's epidermis.<\/p>\r\n\r\n<\/div>\r\n<div id=\"fs-id2378542\" class=\"bc-section section\">\r\n<h3>Microtubules<\/h3>\r\n<p id=\"fs-id1430610\">As their name implies, microtubules are small hollow tubes. Polymerized dimers of \u03b1-tubulin and \u03b2-tubulin, two globular proteins, comprise the microtubule's walls (<a class=\"autogenerated-content\" href=\"#fig-ch04-05-04\">(Figure)<\/a>). With a diameter of about 25 nm, microtubules are cytoskeletons' widest components. They help the cell resist compression, provide a track along which vesicles move through the cell, and pull replicated chromosomes to opposite ends of a dividing cell. Like microfilaments, microtubules can disassemble and reform quickly.<\/p>\r\n\r\n<div id=\"fig-ch04-05-04\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"500\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174653\/Figure_04_05_04ab.jpg\" alt=\"The left part of this figure is a molecular model of 13 polymerized dimers of alpha- and beta-tubulin joined together to form a hollow tube. The right part of this image shows the tubulin structure as a ring of spheres connected together.\" width=\"500\" height=\"426\" \/> <strong>Figure 4. <\/strong>Microtubules are hollow. Their walls consist of 13 polymerized dimers of \u03b1-tubulin and \u03b2-tubulin (right image). The left image shows the tube's molecular structure.[\/caption]\r\n\r\n<\/div>\r\n<p id=\"fs-id1773065\">Microtubules are also the structural elements of flagella, cilia, and centrioles (the latter are the centrosome's two perpendicular bodies). In animal cells, the centrosome is the microtubule-organizing center. In eukaryotic cells, flagella and cilia are quite different structurally from their counterparts in prokaryotes, as we discuss below.<\/p>\r\n\r\n<div class=\"bc-section section\">\r\n<h4>Flagella and Cilia<\/h4>\r\nThe flagella (singular = flagellum) are long, hair-like structures that extend from the plasma membrane and enable an entire cell to move (for example, sperm, <em>Euglena<\/em>, and some prokaryotes). When present, the cell has just one flagellum or a few flagella. However, when cilia (singular = cilium) are present, many of them extend along the plasma membrane's entire surface. They are short, hair-like structures that move entire cells (such as paramecia) or substances along the cell's outer surface (for example, the cilia of cells lining the Fallopian tubes that move the ovum toward the uterus, or cilia lining the cells of the respiratory tract that trap particulate matter and move it toward your nostrils.)\r\n\r\nDespite their differences in length and number, flagella and cilia share a common structural arrangement of microtubules called a \u201c9 + 2 array.\u201d This is an appropriate name because a single flagellum or cilium is made of a ring of nine microtubule doublets, surrounding a single microtubule doublet in the center (<a class=\"autogenerated-content\" href=\"#fig-ch04-05-05\">(Figure)<\/a>).\r\n<div id=\"fig-ch04-05-05\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"275\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174657\/Figure_04_05_05.jpg\" alt=\"This transmission electron micrograph shows a cross section of nine microtubule doublets that form a hollow tube. Another microtubule doublet sits in the center of the tube.\" width=\"275\" height=\"428\" \/> <strong>Figure 5. <\/strong>This transmission electron micrograph of two flagella shows the microtubules' 9 + 2 array: nine microtubule doublets surround a single microtubule doublet. (credit: modification of work by Dartmouth Electron Microscope Facility, Dartmouth College; scale-bar data from Matt Russell)[\/caption]\r\n\r\n<\/div>\r\n<p id=\"fs-id1953479\">You have now completed a broad survey of prokaryotic and eukaryotic cell components. For a summary of cellular components in prokaryotic and eukaryotic cells, see <a class=\"autogenerated-content\" href=\"#tab-ch04-05-01\">(Figure)<\/a>.<\/p>\r\n\r\n<table id=\"tab-ch04-05-01\" summary=\"This table compares the features of prokaryotic and eukaryotic cells, highlighting their different levels of functioning.\">\r\n<thead>\r\n<tr>\r\n<th colspan=\"5\">Components of Prokaryotic and Eukaryotic Cells<\/th>\r\n<\/tr>\r\n<tr>\r\n<th>Cell Component<\/th>\r\n<th>Function<\/th>\r\n<th>Present in Prokaryotes?<\/th>\r\n<th>Present in Animal Cells?<\/th>\r\n<th>Present in Plant Cells?<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tbody>\r\n<tr>\r\n<td>Plasma membrane<\/td>\r\n<td>Separates cell from external environment; controls passage of organic molecules, ions, water, oxygen, and wastes into and out of cell<\/td>\r\n<td>Yes<\/td>\r\n<td>Yes<\/td>\r\n<td>Yes<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Cytoplasm<\/td>\r\n<td>Provides turgor pressure to plant cells as fluid inside the central vacuole; site of many metabolic reactions; medium in which organelles are found<\/td>\r\n<td>Yes<\/td>\r\n<td>Yes<\/td>\r\n<td>Yes<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Nucleolus<\/td>\r\n<td>Darkened area within the nucleus where ribosomal subunits are synthesized.<\/td>\r\n<td>No<\/td>\r\n<td>Yes<\/td>\r\n<td>Yes<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Nucleus<\/td>\r\n<td>Cell organelle that houses DNA and directs synthesis of ribosomes and proteins<\/td>\r\n<td>No<\/td>\r\n<td>Yes<\/td>\r\n<td>Yes<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Ribosomes<\/td>\r\n<td>Protein synthesis<\/td>\r\n<td>Yes<\/td>\r\n<td>Yes<\/td>\r\n<td>Yes<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Mitochondria<\/td>\r\n<td>ATP production\/cellular respiration<\/td>\r\n<td>No<\/td>\r\n<td>Yes<\/td>\r\n<td>Yes<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Peroxisomes<\/td>\r\n<td>Oxidize and thus break down fatty acids and amino acids, and detoxify poisons<\/td>\r\n<td>No<\/td>\r\n<td>Yes<\/td>\r\n<td>Yes<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Vesicles and vacuoles<\/td>\r\n<td>Storage and transport; digestive function in plant cells<\/td>\r\n<td>No<\/td>\r\n<td>Yes<\/td>\r\n<td>Yes<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Centrosome<\/td>\r\n<td>Unspecified role in cell division in animal cells; microtubule source in animal cells<\/td>\r\n<td>No<\/td>\r\n<td>Yes<\/td>\r\n<td>No<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Lysosomes<\/td>\r\n<td>Digestion of macromolecules; recycling of worn-out organelles<\/td>\r\n<td>No<\/td>\r\n<td>Yes<\/td>\r\n<td>Some<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Cell wall<\/td>\r\n<td>Protection, structural support, and maintenance of cell shape<\/td>\r\n<td>Yes, primarily peptidoglycan<\/td>\r\n<td>No<\/td>\r\n<td>Yes, primarily cellulose<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Chloroplasts<\/td>\r\n<td>Photosynthesis<\/td>\r\n<td>No<\/td>\r\n<td>No<\/td>\r\n<td>Yes<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Endoplasmic reticulum<\/td>\r\n<td>Modifies proteins and synthesizes lipids<\/td>\r\n<td>No<\/td>\r\n<td>Yes<\/td>\r\n<td>Yes<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Golgi apparatus<\/td>\r\n<td>Modifies, sorts, tags, packages, and distributes lipids and proteins<\/td>\r\n<td>No<\/td>\r\n<td>Yes<\/td>\r\n<td>Yes<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Cytoskeleton<\/td>\r\n<td>Maintains cell\u2019s shape, secures organelles in specific positions, allows cytoplasm and vesicles to move within cell, and enables unicellular organisms to move independently<\/td>\r\n<td>Yes<\/td>\r\n<td>Yes<\/td>\r\n<td>Yes<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Flagella<\/td>\r\n<td>Cellular locomotion<\/td>\r\n<td>Some<\/td>\r\n<td>Some<\/td>\r\n<td>No, except for some plant sperm cells<\/td>\r\n<\/tr>\r\n<tr>\r\n<td>Cilia<\/td>\r\n<td>Cellular locomotion, movement of particles along plasma membrane's extracellular surface, and filtration<\/td>\r\n<td>Some<\/td>\r\n<td>Some<\/td>\r\n<td>No<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-id1758798\" class=\"summary textbox key-takeaways\">\r\n<h3>Section Summary<\/h3>\r\n<p id=\"fs-id2005174\">The cytoskeleton has three different protein element types. From narrowest to widest, they are the microfilaments (actin filaments), intermediate filaments, and microtubules. Biologists often associate microfilaments with myosin. They provide rigidity and shape to the cell and facilitate cellular movements. Intermediate filaments bear tension and anchor the nucleus and other organelles in place. Microtubules help the cell resist compression, serve as tracks for motor proteins that move vesicles through the cell, and pull replicated chromosomes to opposite ends of a dividing cell. They are also the structural element of centrioles, flagella, and cilia.<\/p>\r\n\r\n<\/div>\r\n<div id=\"fs-id1968455\" class=\"multiple-choice textbox exercises\">\r\n<h3>Review Questions<\/h3>\r\n<div>\r\n<div>\r\n<p id=\"fs-id1973117\">Which of the following have the ability to disassemble and reform quickly?<\/p>\r\n\r\n<ol id=\"fs-id1796676\" type=\"a\">\r\n \t<li>microfilaments and intermediate filaments<\/li>\r\n \t<li>microfilaments and microtubules<\/li>\r\n \t<li>intermediate filaments and microtubules<\/li>\r\n \t<li>only intermediate filaments<\/li>\r\n<\/ol>\r\n<\/div>\r\n<div>\r\n<p id=\"fs-id1366449\">[reveal-answer q=\"242832\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"242832\"]<\/p>\r\nB[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-id2219667\">\r\n<div id=\"fs-id2215371\">\r\n\r\nWhich of the following do not play a role in intracellular movement?\r\n<ol id=\"fs-id949079\" type=\"a\">\r\n \t<li>microfilaments and intermediate filaments<\/li>\r\n \t<li>microfilaments and microtubules<\/li>\r\n \t<li>intermediate filaments and microtubules<\/li>\r\n \t<li>only intermediate filaments<\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-id1430811\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-id1430811\"]\r\n<div id=\"fs-id1430811\">\r\n<p id=\"fs-id1465956\">D<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-idm71000714\">\r\n<div id=\"fs-idp81418441\">\r\n<p id=\"fs-idm74380426\">In humans, _____ are used to move a cell within its environment while _____ are used to move the environment relative to the cell.<\/p>\r\n\r\n<ol id=\"fs-idm67922765\" type=\"a\">\r\n \t<li>cilia, pseudopodia<\/li>\r\n \t<li>flagella; cilia<\/li>\r\n \t<li>microtubules; flagella<\/li>\r\n \t<li>microfilaments; microtubules<\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-idm40512369\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idm40512369\"]\r\n<div id=\"fs-idm40512369\">\r\n<p id=\"fs-idm200102075\">B<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-id1670750\" class=\"free-response textbox exercises\">\r\n<h3>Free Response<\/h3>\r\n<div id=\"fs-id802695\">\r\n<div id=\"fs-id1453364\">\r\n<p id=\"fs-id1320817\">What are the similarities and differences between the structures of centrioles and flagella?<\/p>\r\n\r\n<\/div>\r\n[reveal-answer q=\"fs-id1322066\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-id1322066\"]\r\n<div id=\"fs-id1322066\">\r\n<p id=\"fs-id1431607\">Centrioles and flagella are alike in that they are made up of microtubules. In centrioles, two rings of nine microtubule \u201ctriplets\u201d are arranged at right angles to one another. This arrangement does not occur in flagella.<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-id1649129\">\r\n<div id=\"fs-id1322776\">\r\n<p id=\"fs-id1720446\">How do cilia and flagella differ?<\/p>\r\n\r\n<\/div>\r\n[reveal-answer q=\"fs-id1448091\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-id1448091\"]\r\n<div id=\"fs-id1448091\">\r\n<p id=\"fs-id1105152\">Cilia and flagella are alike in that they are made up of microtubules. Cilia are short, hair-like structures that exist in large numbers and usually cover the entire surface of the plasma membrane. Flagella, in contrast, are long, hair-like structures; when flagella are present, a cell has just one or two.<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-idm71000712\">\r\n<div id=\"fs-idp81418439\">\r\n<p id=\"fs-idm74380424\">Describe how microfilaments and microtubules are involved in the phagocytosis and destruction of a pathogen by a macrophage.<\/p>\r\n\r\n<\/div>\r\n[reveal-answer q=\"fs-idm40512367\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idm40512367\"]\r\n<div id=\"fs-idm40512367\">\r\n<p id=\"fs-idm200102073\">A macrophage engulfs a pathogen by rearranging its actin microfilaments to bend the plasma membrane around the pathogen. Once the pathogen is sealed in an endosome inside the macrophage, the vesicle is walked along microtubules until it combines with a lysosome to digest the pathogen.<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-idm71000713\">\r\n<div id=\"fs-idp81418440\">\r\n<p id=\"fs-idm74380425\">Compare and contrast the boundaries that plant, animal, and bacteria cells use to separate themselves from their surrounding environment.<\/p>\r\n\r\n<\/div>\r\n[reveal-answer q=\"fs-idm40512368\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idm40512368\"]\r\n<div id=\"fs-idm40512368\">\r\n<p id=\"fs-idm200102074\">All three cell types have a plasma membrane that borders the cytoplasm on its interior side. In animal cells, the exterior side of the plasma membrane is in contact with the extracellular environment. However, in plant and bacteria cells, a cell wall surrounds the outside of the plasma membrane. In plants, the cell wall is made of cellulose, while in bacteria the cell wall is made of peptidoglycan. Gram-negative bacteria also have an additional capsule made of lipopolysaccharides that surrounds their cell wall.<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3>Glossary<\/h3>\r\n<dl id=\"fs-id2472145\">\r\n \t<dt>cilium<\/dt>\r\n \t<dd id=\"fs-id1704493\">(plural = cilia) short, hair-like structure that extends from the plasma membrane in large numbers and functions to move an entire cell or move substances along the cell's outer surface<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1526841\">\r\n \t<dt>cytoskeleton<\/dt>\r\n \t<dd id=\"fs-id1774415\">protein fiber network that collectively maintains the cell's shape, secures some organelles in specific positions, allows cytoplasm and vesicles to move within the cell, and enables unicellular organisms to move independently<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1448192\">\r\n \t<dt>flagellum<\/dt>\r\n \t<dd id=\"fs-id1973989\">(plural = flagella) long, hair-like structure that extends from the plasma membrane and moves the cell<\/dd>\r\n<\/dl>\r\n<dl>\r\n \t<dt>intermediate filament<\/dt>\r\n \t<dd id=\"fs-id1883769\">cytoskeletal component, comprised of several fibrous protein intertwined strands, that bears tension, supports cell-cell junctions, and anchors cells to extracellular structures<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id1805178\">\r\n \t<dt>microfilament<\/dt>\r\n \t<dd id=\"fs-id1968369\">the cytoskeleton system's narrowest element; it provides rigidity and shape to the cell and enables cellular movements<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-id2005388\">\r\n \t<dt>microtubule<\/dt>\r\n \t<dd id=\"fs-id1699781\">the cytoskeleton system's widest element; it helps the cell resist compression, provides a track along which vesicles move through the cell, pulls replicated chromosomes to opposite ends of a dividing cell, and is the structural element of centrioles, flagella, and cilia<\/dd>\r\n<\/dl>\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<p>By the end of this section, you will be able to do the following:<\/p>\n<ul>\n<li>Describe the cytoskeleton<\/li>\n<li>Compare the roles of microfilaments, intermediate filaments, and microtubules<\/li>\n<li>Compare and contrast cilia and flagella<\/li>\n<li>Summarize the differences among the components of prokaryotic cells, animal cells, and plant cells<\/li>\n<\/ul>\n<\/div>\n<p>If you were to remove all the organelles from a cell, would the plasma membrane and the cytoplasm be the only components left? No. Within the cytoplasm, there would still be ions and organic molecules, plus a network of protein fibers that help maintain the cell&#8217;s shape, secure some organelles in specific positions, allow cytoplasm and vesicles to move within the cell, and enable cells within multicellular organisms to move. Collectively, scientists call this network of protein fibers the cytoskeleton. There are three types of fibers within the cytoskeleton: microfilaments, intermediate filaments, and microtubules (<a class=\"autogenerated-content\" href=\"#fig-ch04-05-01\">(Figure)<\/a>). Here, we will examine each.<\/p>\n<div id=\"fig-ch04-05-01\" class=\"wp-caption aligncenter\">\n<div style=\"width: 285px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174645\/Figure_04_05_01.jpg\" alt=\"Microfilaments line the inside of the plasma membrane, whereas microfilaments radiate out from the center of the cell. Intermediate filaments form a network throughout the cell that holds organelles in place.\" width=\"275\" height=\"694\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 1. <\/strong>Microfilaments thicken the cortex around the cell&#8217;s inner edge. Like rubber bands, they resist tension. There are microtubules in the cell&#8217;s interior where they maintain their shape by resisting compressive forces. There are intermediate filaments throughout the cell that hold organelles in place.<\/p>\n<\/div>\n<\/div>\n<div id=\"fs-id1228137\" class=\"bc-section section\">\n<h3>Microfilaments<\/h3>\n<p id=\"fs-id1662602\">Of the three types of protein fibers in the cytoskeleton, microfilaments are the narrowest. They function in cellular movement, have a diameter of about 7 nm, and are comprised of two globular protein intertwined strands, which we call actin (<a class=\"autogenerated-content\" href=\"#fig-ch04-05-02\">(Figure)<\/a>). For this reason, we also call microfilaments actin filaments.<\/p>\n<div id=\"fig-ch04-05-02\" class=\"wp-caption aligncenter\">\n<div style=\"width: 285px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174648\/Figure_04_05_02.jpg\" alt=\"This illustration shows two actin filaments wound together. Each actin filament is composed of many actin subunits connected together to form a chain.\" width=\"275\" height=\"753\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 2. <\/strong>Two intertwined actin strands comprise microfilaments.<\/p>\n<\/div>\n<\/div>\n<p>ATP powers actin to assemble its filamentous form, which serves as a track for the movement of a motor protein we call myosin. This enables actin to engage in cellular events requiring motion, such as cell division in eukaryotic cells and cytoplasmic streaming, which is the cell cytoplasm&#8217;s circular movement in plant cells. Actin and myosin are plentiful in muscle cells. When your actin and myosin filaments slide past each other, your muscles contract.<\/p>\n<p id=\"fs-id1973921\">Microfilaments also provide some rigidity and shape to the cell. They can depolymerize (disassemble) and reform quickly, thus enabling a cell to change its shape and move. White blood cells (your body\u2019s infection-fighting cells) make good use of this ability. They can move to an infection site and phagocytize the pathogen.<\/p>\n<div id=\"fs-id1685480\" class=\"interactive textbox tryit\">\n<h3>Link to Learning<\/h3>\n<p id=\"fs-id1364358\">To see an example of a white blood cell in action, watch a short time-lapse <a href=\"https:\/\/youtu.be\/AUih856vaQY\">video<\/a> of the cell capturing two bacteria. It engulfs one and then moves on to the other.<\/p>\n<div id=\"eip-id3083425\"><\/div>\n<\/div>\n<\/div>\n<div id=\"fs-id1361987\" class=\"bc-section section\">\n<h3>Intermediate Filaments<\/h3>\n<p id=\"fs-id1358496\">Several strands of fibrous proteins that are wound together comprise intermediate filaments (<a class=\"autogenerated-content\" href=\"#fig-ch04-05-03\">(Figure)<\/a>). Cytoskeleton elements get their name from the fact that their diameter, 8 to 10 nm, is between those of microfilaments and microtubules.<\/p>\n<div id=\"fig-ch04-05-03\" class=\"wp-caption aligncenter\">\n<div style=\"width: 360px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174650\/Figure_04_05_03.jpg\" alt=\"This illustration shows 10 intermediate filament fibers bundled together.\" width=\"350\" height=\"116\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 3. <\/strong>Intermediate filaments consist of several intertwined strands of fibrous proteins.<\/p>\n<\/div>\n<\/div>\n<p id=\"fs-id1561464\">Intermediate filaments have no role in cell movement. Their function is purely structural. They bear tension, thus maintaining the cell&#8217;s shape, and anchor the nucleus and other organelles in place. <a class=\"autogenerated-content\" href=\"#fig-ch04-05-01\">(Figure)<\/a> shows how intermediate filaments create a supportive scaffolding inside the cell.<\/p>\n<p id=\"fs-id1232860\">The intermediate filaments are the most diverse group of cytoskeletal elements. Several fibrous protein types are in the intermediate filaments. You are probably most familiar with keratin, the fibrous protein that strengthens your hair, nails, and the skin&#8217;s epidermis.<\/p>\n<\/div>\n<div id=\"fs-id2378542\" class=\"bc-section section\">\n<h3>Microtubules<\/h3>\n<p id=\"fs-id1430610\">As their name implies, microtubules are small hollow tubes. Polymerized dimers of \u03b1-tubulin and \u03b2-tubulin, two globular proteins, comprise the microtubule&#8217;s walls (<a class=\"autogenerated-content\" href=\"#fig-ch04-05-04\">(Figure)<\/a>). With a diameter of about 25 nm, microtubules are cytoskeletons&#8217; widest components. They help the cell resist compression, provide a track along which vesicles move through the cell, and pull replicated chromosomes to opposite ends of a dividing cell. Like microfilaments, microtubules can disassemble and reform quickly.<\/p>\n<div id=\"fig-ch04-05-04\">\n<div style=\"width: 510px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174653\/Figure_04_05_04ab.jpg\" alt=\"The left part of this figure is a molecular model of 13 polymerized dimers of alpha- and beta-tubulin joined together to form a hollow tube. The right part of this image shows the tubulin structure as a ring of spheres connected together.\" width=\"500\" height=\"426\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 4. <\/strong>Microtubules are hollow. Their walls consist of 13 polymerized dimers of \u03b1-tubulin and \u03b2-tubulin (right image). The left image shows the tube&#8217;s molecular structure.<\/p>\n<\/div>\n<\/div>\n<p id=\"fs-id1773065\">Microtubules are also the structural elements of flagella, cilia, and centrioles (the latter are the centrosome&#8217;s two perpendicular bodies). In animal cells, the centrosome is the microtubule-organizing center. In eukaryotic cells, flagella and cilia are quite different structurally from their counterparts in prokaryotes, as we discuss below.<\/p>\n<div class=\"bc-section section\">\n<h4>Flagella and Cilia<\/h4>\n<p>The flagella (singular = flagellum) are long, hair-like structures that extend from the plasma membrane and enable an entire cell to move (for example, sperm, <em>Euglena<\/em>, and some prokaryotes). When present, the cell has just one flagellum or a few flagella. However, when cilia (singular = cilium) are present, many of them extend along the plasma membrane&#8217;s entire surface. They are short, hair-like structures that move entire cells (such as paramecia) or substances along the cell&#8217;s outer surface (for example, the cilia of cells lining the Fallopian tubes that move the ovum toward the uterus, or cilia lining the cells of the respiratory tract that trap particulate matter and move it toward your nostrils.)<\/p>\n<p>Despite their differences in length and number, flagella and cilia share a common structural arrangement of microtubules called a \u201c9 + 2 array.\u201d This is an appropriate name because a single flagellum or cilium is made of a ring of nine microtubule doublets, surrounding a single microtubule doublet in the center (<a class=\"autogenerated-content\" href=\"#fig-ch04-05-05\">(Figure)<\/a>).<\/p>\n<div id=\"fig-ch04-05-05\" class=\"wp-caption aligncenter\">\n<div style=\"width: 285px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03174657\/Figure_04_05_05.jpg\" alt=\"This transmission electron micrograph shows a cross section of nine microtubule doublets that form a hollow tube. Another microtubule doublet sits in the center of the tube.\" width=\"275\" height=\"428\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 5. <\/strong>This transmission electron micrograph of two flagella shows the microtubules&#8217; 9 + 2 array: nine microtubule doublets surround a single microtubule doublet. (credit: modification of work by Dartmouth Electron Microscope Facility, Dartmouth College; scale-bar data from Matt Russell)<\/p>\n<\/div>\n<\/div>\n<p id=\"fs-id1953479\">You have now completed a broad survey of prokaryotic and eukaryotic cell components. For a summary of cellular components in prokaryotic and eukaryotic cells, see <a class=\"autogenerated-content\" href=\"#tab-ch04-05-01\">(Figure)<\/a>.<\/p>\n<table id=\"tab-ch04-05-01\" summary=\"This table compares the features of prokaryotic and eukaryotic cells, highlighting their different levels of functioning.\">\n<thead>\n<tr>\n<th colspan=\"5\">Components of Prokaryotic and Eukaryotic Cells<\/th>\n<\/tr>\n<tr>\n<th>Cell Component<\/th>\n<th>Function<\/th>\n<th>Present in Prokaryotes?<\/th>\n<th>Present in Animal Cells?<\/th>\n<th>Present in Plant Cells?<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Plasma membrane<\/td>\n<td>Separates cell from external environment; controls passage of organic molecules, ions, water, oxygen, and wastes into and out of cell<\/td>\n<td>Yes<\/td>\n<td>Yes<\/td>\n<td>Yes<\/td>\n<\/tr>\n<tr>\n<td>Cytoplasm<\/td>\n<td>Provides turgor pressure to plant cells as fluid inside the central vacuole; site of many metabolic reactions; medium in which organelles are found<\/td>\n<td>Yes<\/td>\n<td>Yes<\/td>\n<td>Yes<\/td>\n<\/tr>\n<tr>\n<td>Nucleolus<\/td>\n<td>Darkened area within the nucleus where ribosomal subunits are synthesized.<\/td>\n<td>No<\/td>\n<td>Yes<\/td>\n<td>Yes<\/td>\n<\/tr>\n<tr>\n<td>Nucleus<\/td>\n<td>Cell organelle that houses DNA and directs synthesis of ribosomes and proteins<\/td>\n<td>No<\/td>\n<td>Yes<\/td>\n<td>Yes<\/td>\n<\/tr>\n<tr>\n<td>Ribosomes<\/td>\n<td>Protein synthesis<\/td>\n<td>Yes<\/td>\n<td>Yes<\/td>\n<td>Yes<\/td>\n<\/tr>\n<tr>\n<td>Mitochondria<\/td>\n<td>ATP production\/cellular respiration<\/td>\n<td>No<\/td>\n<td>Yes<\/td>\n<td>Yes<\/td>\n<\/tr>\n<tr>\n<td>Peroxisomes<\/td>\n<td>Oxidize and thus break down fatty acids and amino acids, and detoxify poisons<\/td>\n<td>No<\/td>\n<td>Yes<\/td>\n<td>Yes<\/td>\n<\/tr>\n<tr>\n<td>Vesicles and vacuoles<\/td>\n<td>Storage and transport; digestive function in plant cells<\/td>\n<td>No<\/td>\n<td>Yes<\/td>\n<td>Yes<\/td>\n<\/tr>\n<tr>\n<td>Centrosome<\/td>\n<td>Unspecified role in cell division in animal cells; microtubule source in animal cells<\/td>\n<td>No<\/td>\n<td>Yes<\/td>\n<td>No<\/td>\n<\/tr>\n<tr>\n<td>Lysosomes<\/td>\n<td>Digestion of macromolecules; recycling of worn-out organelles<\/td>\n<td>No<\/td>\n<td>Yes<\/td>\n<td>Some<\/td>\n<\/tr>\n<tr>\n<td>Cell wall<\/td>\n<td>Protection, structural support, and maintenance of cell shape<\/td>\n<td>Yes, primarily peptidoglycan<\/td>\n<td>No<\/td>\n<td>Yes, primarily cellulose<\/td>\n<\/tr>\n<tr>\n<td>Chloroplasts<\/td>\n<td>Photosynthesis<\/td>\n<td>No<\/td>\n<td>No<\/td>\n<td>Yes<\/td>\n<\/tr>\n<tr>\n<td>Endoplasmic reticulum<\/td>\n<td>Modifies proteins and synthesizes lipids<\/td>\n<td>No<\/td>\n<td>Yes<\/td>\n<td>Yes<\/td>\n<\/tr>\n<tr>\n<td>Golgi apparatus<\/td>\n<td>Modifies, sorts, tags, packages, and distributes lipids and proteins<\/td>\n<td>No<\/td>\n<td>Yes<\/td>\n<td>Yes<\/td>\n<\/tr>\n<tr>\n<td>Cytoskeleton<\/td>\n<td>Maintains cell\u2019s shape, secures organelles in specific positions, allows cytoplasm and vesicles to move within cell, and enables unicellular organisms to move independently<\/td>\n<td>Yes<\/td>\n<td>Yes<\/td>\n<td>Yes<\/td>\n<\/tr>\n<tr>\n<td>Flagella<\/td>\n<td>Cellular locomotion<\/td>\n<td>Some<\/td>\n<td>Some<\/td>\n<td>No, except for some plant sperm cells<\/td>\n<\/tr>\n<tr>\n<td>Cilia<\/td>\n<td>Cellular locomotion, movement of particles along plasma membrane&#8217;s extracellular surface, and filtration<\/td>\n<td>Some<\/td>\n<td>Some<\/td>\n<td>No<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<div id=\"fs-id1758798\" class=\"summary textbox key-takeaways\">\n<h3>Section Summary<\/h3>\n<p id=\"fs-id2005174\">The cytoskeleton has three different protein element types. From narrowest to widest, they are the microfilaments (actin filaments), intermediate filaments, and microtubules. Biologists often associate microfilaments with myosin. They provide rigidity and shape to the cell and facilitate cellular movements. Intermediate filaments bear tension and anchor the nucleus and other organelles in place. Microtubules help the cell resist compression, serve as tracks for motor proteins that move vesicles through the cell, and pull replicated chromosomes to opposite ends of a dividing cell. They are also the structural element of centrioles, flagella, and cilia.<\/p>\n<\/div>\n<div id=\"fs-id1968455\" class=\"multiple-choice textbox exercises\">\n<h3>Review Questions<\/h3>\n<div>\n<div>\n<p id=\"fs-id1973117\">Which of the following have the ability to disassemble and reform quickly?<\/p>\n<ol id=\"fs-id1796676\" type=\"a\">\n<li>microfilaments and intermediate filaments<\/li>\n<li>microfilaments and microtubules<\/li>\n<li>intermediate filaments and microtubules<\/li>\n<li>only intermediate filaments<\/li>\n<\/ol>\n<\/div>\n<div>\n<p id=\"fs-id1366449\">\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q242832\">Show Solution<\/span><\/p>\n<div id=\"q242832\" class=\"hidden-answer\" style=\"display: none\">\n<p>B<\/p><\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-id2219667\">\n<div id=\"fs-id2215371\">\n<p>Which of the following do not play a role in intracellular movement?<\/p>\n<ol id=\"fs-id949079\" type=\"a\">\n<li>microfilaments and intermediate filaments<\/li>\n<li>microfilaments and microtubules<\/li>\n<li>intermediate filaments and microtubules<\/li>\n<li>only intermediate filaments<\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-id1430811\">Show Solution<\/span><\/p>\n<div id=\"qfs-id1430811\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-id1430811\">\n<p id=\"fs-id1465956\">D<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm71000714\">\n<div id=\"fs-idp81418441\">\n<p id=\"fs-idm74380426\">In humans, _____ are used to move a cell within its environment while _____ are used to move the environment relative to the cell.<\/p>\n<ol id=\"fs-idm67922765\" type=\"a\">\n<li>cilia, pseudopodia<\/li>\n<li>flagella; cilia<\/li>\n<li>microtubules; flagella<\/li>\n<li>microfilaments; microtubules<\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idm40512369\">Show Solution<\/span><\/p>\n<div id=\"qfs-idm40512369\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idm40512369\">\n<p id=\"fs-idm200102075\">B<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-id1670750\" class=\"free-response textbox exercises\">\n<h3>Free Response<\/h3>\n<div id=\"fs-id802695\">\n<div id=\"fs-id1453364\">\n<p id=\"fs-id1320817\">What are the similarities and differences between the structures of centrioles and flagella?<\/p>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-id1322066\">Show Solution<\/span><\/p>\n<div id=\"qfs-id1322066\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-id1322066\">\n<p id=\"fs-id1431607\">Centrioles and flagella are alike in that they are made up of microtubules. In centrioles, two rings of nine microtubule \u201ctriplets\u201d are arranged at right angles to one another. This arrangement does not occur in flagella.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-id1649129\">\n<div id=\"fs-id1322776\">\n<p id=\"fs-id1720446\">How do cilia and flagella differ?<\/p>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-id1448091\">Show Solution<\/span><\/p>\n<div id=\"qfs-id1448091\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-id1448091\">\n<p id=\"fs-id1105152\">Cilia and flagella are alike in that they are made up of microtubules. Cilia are short, hair-like structures that exist in large numbers and usually cover the entire surface of the plasma membrane. Flagella, in contrast, are long, hair-like structures; when flagella are present, a cell has just one or two.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm71000712\">\n<div id=\"fs-idp81418439\">\n<p id=\"fs-idm74380424\">Describe how microfilaments and microtubules are involved in the phagocytosis and destruction of a pathogen by a macrophage.<\/p>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idm40512367\">Show Solution<\/span><\/p>\n<div id=\"qfs-idm40512367\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idm40512367\">\n<p id=\"fs-idm200102073\">A macrophage engulfs a pathogen by rearranging its actin microfilaments to bend the plasma membrane around the pathogen. Once the pathogen is sealed in an endosome inside the macrophage, the vesicle is walked along microtubules until it combines with a lysosome to digest the pathogen.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm71000713\">\n<div id=\"fs-idp81418440\">\n<p id=\"fs-idm74380425\">Compare and contrast the boundaries that plant, animal, and bacteria cells use to separate themselves from their surrounding environment.<\/p>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idm40512368\">Show Solution<\/span><\/p>\n<div id=\"qfs-idm40512368\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idm40512368\">\n<p id=\"fs-idm200102074\">All three cell types have a plasma membrane that borders the cytoplasm on its interior side. In animal cells, the exterior side of the plasma membrane is in contact with the extracellular environment. However, in plant and bacteria cells, a cell wall surrounds the outside of the plasma membrane. In plants, the cell wall is made of cellulose, while in bacteria the cell wall is made of peptidoglycan. Gram-negative bacteria also have an additional capsule made of lipopolysaccharides that surrounds their cell wall.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox shaded\">\n<h3>Glossary<\/h3>\n<dl id=\"fs-id2472145\">\n<dt>cilium<\/dt>\n<dd id=\"fs-id1704493\">(plural = cilia) short, hair-like structure that extends from the plasma membrane in large numbers and functions to move an entire cell or move substances along the cell&#8217;s outer surface<\/dd>\n<\/dl>\n<dl id=\"fs-id1526841\">\n<dt>cytoskeleton<\/dt>\n<dd id=\"fs-id1774415\">protein fiber network that collectively maintains the cell&#8217;s shape, secures some organelles in specific positions, allows cytoplasm and vesicles to move within the cell, and enables unicellular organisms to move independently<\/dd>\n<\/dl>\n<dl id=\"fs-id1448192\">\n<dt>flagellum<\/dt>\n<dd id=\"fs-id1973989\">(plural = flagella) long, hair-like structure that extends from the plasma membrane and moves the cell<\/dd>\n<\/dl>\n<dl>\n<dt>intermediate filament<\/dt>\n<dd id=\"fs-id1883769\">cytoskeletal component, comprised of several fibrous protein intertwined strands, that bears tension, supports cell-cell junctions, and anchors cells to extracellular structures<\/dd>\n<\/dl>\n<dl id=\"fs-id1805178\">\n<dt>microfilament<\/dt>\n<dd id=\"fs-id1968369\">the cytoskeleton system&#8217;s narrowest element; it provides rigidity and shape to the cell and enables cellular movements<\/dd>\n<\/dl>\n<dl id=\"fs-id2005388\">\n<dt>microtubule<\/dt>\n<dd id=\"fs-id1699781\">the cytoskeleton system&#8217;s widest element; it helps the cell resist compression, provides a track along which vesicles move through the cell, pulls replicated chromosomes to opposite ends of a dividing cell, and is the structural element of centrioles, flagella, and cilia<\/dd>\n<\/dl>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-577\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Biology 2e. <strong>Provided by<\/strong>: OpenStax. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"https:\/\/openstax.org\/details\/books\/biology-2e\">https:\/\/openstax.org\/details\/books\/biology-2e<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Download for free at http:\/\/cnx.org\/contents\/8d50a0af-948b-4204-a71d-4826cba765b8@8.19<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":311,"menu_order":6,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology 2e\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"https:\/\/openstax.org\/details\/books\/biology-2e\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at http:\/\/cnx.org\/contents\/8d50a0af-948b-4204-a71d-4826cba765b8@8.19\"}]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-577","chapter","type-chapter","status-publish","hentry"],"part":542,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/577","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/users\/311"}],"version-history":[{"count":4,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/577\/revisions"}],"predecessor-version":[{"id":2449,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/577\/revisions\/2449"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/parts\/542"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/577\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/media?parent=577"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapter-type?post=577"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/contributor?post=577"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/license?post=577"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}