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The Cell: Cytoskeleton
AP Biology
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Cytoskeleton Function structural support motility regulation
maintains shape of cell provides anchorage for organelles motility cell locomotion cilia, flagella, etc. regulation organizes structures & activities of cell AP Biology
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Cytoskeleton Structure
network of fibers extending throughout cytoplasm 3 main protein fibers microtubules microfilaments intermediate filaments It’s a matter of size… AP Biology
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Evolutionary perspective
Proteins that make up the fibers are very similar in all living things from bacteria to humans tubulin (all cells) actin (eukaryote cells) Means that they are both ancient and essential for life AP Biology
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Microtubules Structure thickest fibers
hollow rods about 25nm in diameter constructed of protein, tubulin grow or shrink as more tubulin molecules are added or removed AP Biology
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Microtubules Function structural support & cell movement
move chromosomes during cell division centrioles tracks that guide motor proteins carrying organelles to their destination motor proteins: myosin & dynein motility cilia flagella AP Biology
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Centrioles Cell division
in animal cells, pair of centrioles organize microtubules guiding chromosomes in cell division AP Biology
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Cilia & flagella Extensions of eukaryotic cytoskeleton
Cilia = numerous & short (hair-like) Flagella = 1-2/cell & longer (whip-like) move unicellular & small multicellular organisms by propelling water past them cilia sweep mucus & debris from lungs flagellum of sperm cells AP Biology
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Cilia Oar-like movement alternating power & recovery strokes
generate force perpendicular to cilia’s axis AP Biology
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Flagella undulatory movement
force generated parallel to flagellum’s axis AP Biology
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Cilia & Flagella Structure remember 9+2!
9 pairs of microtubules around 2 single microtubules in center bending of cilia & flagella is driven by motor protein dynein requires ATP AP Biology
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Microfilaments (actin filaments)
Structure thinnest class of fibers solid rods of protein, actin twisted double chain of actin subunits about 7nm in diameter Function 3-D network inside cell membrane in muscle cells, actin filaments interact with myosin filaments to create muscle contraction AP Biology
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Microfilaments (actin filaments)
“ Microfilaments (actin filaments) Dynamic process actin filaments constantly form & dissolve making the cytoplasm liquid or stiff during movement movement of Amoeba cytoplasmic streaming in plant cells speeds distribution of materials AP Biology
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Intermediate filaments
Structure specialized for bearing tension built from keratin proteins same protein as hair intermediate in size 8-12nm Function hold “things” in place inside cell more permanent fixtures of cytoskeleton reinforce cell shape & fix organelle location nucleus is held in place by a network of intermediate filaments AP Biology
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Summary Microtubules Microfilaments Intermediate filaments • actin
thickest cell structure & cell motility tubulin Microfilaments thinnest internal movements within cell actin, myosin Intermediate filaments intermediate more permanent fixtures keratin • actin • microtubule • nuclei AP Biology
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Cell Junctions Where cells touch each other… AP Biology
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Plant cell wall Structure cellulose primary cell wall
secondary cell wall middle lamella = sticky polysaccharides AP Biology
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Intercellular junctions
Plant cells plasmodesmata channels allowing cytosol to pass between cells plasmodesmata AP Biology
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Animal cell surface Extracellular matrix
collagen fibers in network of glycoproteins support adhesion movement regulation AP Biology
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Intercellular junctions in animals
AP Biology
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Intercellular junctions
Animal cells tight junctions membranes of adjacent cells fused forming barrier between cells forces material through cell membrane gap junctions communicating junctions allow cytoplasmic movement between adjacent cells desmosomes anchoring junctions fasten cells together in strong sheets AP Biology
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A cell is a living unit greater than the sum of its parts
AP Biology
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