Cytoskeleton, Cell Walls, & ECM Slide show modified from: http://www.explorebiology.com Cytoskeleton, Cell Walls, & ECM

Cytoskeleton – network of fibers extending throughout the cytoplasm

MICROTUBULES FUNCTION Structural support and cell movement ~ Move chromosomes during cell division Centrioles & spindle fibers ~ tracks guide motor proteins Motor proteins: dynein & myosin ~ cell motility Cilia & flagella

http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb2/part1/movies/kinesin.dcr MICROTUBULES Tracks guide motor proteins to destination (Motor proteins: dynein & myosin) Vesicle Receptor for motor protein Motor protein (ATP powered) Microtubule of cytoskeleton ATP SEE MOTOR PROTEINS in ACTION EXAMPLES Vesicles containing neurotransmitters migrate to tips of nerve cells Vesicles move to Golgi along cytoskeletal tracks Cytoplasmic streaming http://python.rice.edu/~kolomeisky/transport.htm

Cilia and Flagella Are locomotor appendages Extensions of cytoskeleton Examples: Many unicellular protists move with flagella Some plant reproductive cells have flagella Cilia in oviducts move egg toward uterus Cilia lining windpipe sweep mucous out of lungs Flagellum in sperm cells (Prokaryotic flagella don’t have microtubules)

Cross section of basal body Cilia and flagella share a common ultrastructure (b) Outer microtubule doublet Dynein arms Central microtubule Outer doublets cross-linking proteins inside Radial spoke Plasma membrane Microtubules Basal body 0.5 µm 0.1 µm Cross section of basal body Triplet

FLAGELLUM (few, long) whip-like movement; cell moves in same direction as axis of flagellum CILIUM (many, short) oar-like movement; cell moves perpendicular to axis of cilium http://web.jjay.cuny.edu/~acarpi/NSC/13-cells.htm http://www.sk.lung.ca/content.cfm?edit_realword=hwbreathe

MICROFILAMENTS STRUCTURE Thinnest class of fibers Twisted double chain of actin subunits ~ 7 nm in diameter FUNCTION Crosslinks with microtubules (cell shape) Muscle cells: Actin filaments interact with myosin motor proteins to create muscle contraction Amoeboid movement Cytoplasmic streaming

MICROFILAMENTS Make up contractile apparatus of muscle Contain the motor protein myosin in addition to actin Actin filament Myosin filament Myosin motors in muscle cell contraction. (a) Muscle cell Myosin arm

Amoeboid movement Actin filaments constantly form & dissolve making cytoplasm liquid or stiff during movement Cortex (outer cytoplasm): gel with actin network Inner cytoplasm: sol with actin subunits Extending pseudopodium http://www.nextftp.com/jissen/ameba.gif

Cytoplasmic streaming Speeds distribution of materials http://www.daviddarling.info/images/cytoplasmic_streaming.gif Nonmoving cytoplasm (gel) Chloroplast Streaming cytoplasm (sol) Parallel actin filaments Cell wall

NUCLEAR LAMINA

Cell Walls of Plants Protection Maintain shape Also found in Prokaryotes, fungi, and some protists Composition varies with species/cell type Basic design: Microfibrils of polysaccharide cellulose embedded in matrix of other polysaccharides (like steel reinforced concrete)

MIDDLE LAMELLA- ~ between primary cell walls of adjacent cells Plant cell wall Structure PRIMARY CELL WALL MIDDLE LAMELLA- ~ between primary cell walls of adjacent cells ~ made of sticky polysaccharides (pectins) ~ glues cells together SECONDARY CELL WALL ~ built when cell stops growing ~ between plasma membrane and 1° cell wall

Unify plant into one living continum

Types of intercellular junctions in animals TIGHT JUNCTIONS Membranes of neighboring cells and pressed together & bound by proteins Forms continuous seal to prevent leakage of extracellular fluid across layer of cells DESMOSOMES (anchoring junctions) Act like “rivets” to fasten cells together into strong sheets Intermediate proteins (keratin) anchor desmosomes in cytoplasm GAP JUNCTIONS (communicating junctions) Channels connect to adjacent cells Special membrane proteins surround pore Necessary for communication between cells in heart muscle and animal embryos

The Cell: A Living Unit Greater Than the Sum of Its Parts Cells rely on the integration of structures and organelles in order to function 5 µm Figure 6.32