1. The Cytoskeleton... Is a supportive meshwork of fine fibers inside eukaryotic cells Provides structural support Is involved in cell movement and movement of organelles within cells May help regulate cellular activities FIGURE 1: CYTOSKELETON OF A CELL HIGHLIGHTED IN GREEN

2. Microfilaments Fine, threaded protein fibers Consists of Actin, a globular, contractile (can contract under stimuli-see next point) protein, one of the most abundant cellular proteins Has myosin proteins (motor), activated by an ATP, causing movement along the actin fibers, causing contraction in the filament, and therefore muscle contraction 3-6 nanometers in diameter Carry out cellular movement such as gliding, contraction, and cytokinesis (cytoplasm division of eukaryotic cells) FIGURE 3: ATP ACTIVATED MYOSIN MOTOR PROTEIN “WALKING” ON AN ACTIN MICROFIBER, CAUSING IT TO CONTRACT FIGURE 4: ARRANGEMENT OF ACTIN GLOBULAR PROTEINS IN A MICROFILAMENT

3. Microtubules Cylindrical tubes consisting of tubulin (globular protein) in subunits (two tubulin molecules per subunit) 20-25 nanometers in diameter Determine cell shape and create pathway for cellular movement Serve as spindle fibers for separation of chromosomes in mitosis Constitute cilium and flagellum for cell locomotion/propulsion (see slide on flagellum and cilia) FIGURE 5: TUBULIN SUBUNITS FORMING A MICROTUBUL E FIGURE 6: PINK FIBERS ARE MICROTUBULES SERVING AS SPINDLE FIBERS IN CYTOKINESIS

4. Intermediate Filaments Consist of a variety of fibrous proteins in subunits 10 nanometers in diameter (in between microtubules and microfilaments) Serve as anchors for organelles Provide tensile strength and stability for the cell Different proteins form different intermediate filaments Keratin intermediate filaments, for example, are essential in hair and nails and epithelial cells Vimentins give strength to muscles FIGURE 7: VAST NETWORK OF KERATIN INTERMEDIATE FILAMENTS IN AN ANIMAL CELL STRENGTH AND INTEGRITY

5. Microtubules as Locomotives In a cilia or flagella strand, microtubules double up In a 9+2 pattern, 8 pairs of microtubules form a ring, and a ninth pair in the center All nine pairs are coated with an extension of the plasma membrane of the cell The basal body, or bottom supporting structure of the cilia/flagella, consists of 9 triplets of microtubules Cause movement by a dynein (protein) arm on a certain microtubule grabbing an adjacent one (powered by an ATP) and “walk” on the adjacent one, causing a sliding force. Because the microtubule doublets are held together, they must bend, causing cellular propulsion FIGURE 9: BENDING OF MICROTUBULES FIGURE 8

6. The Extracellular matrix... Is a layer of glycoproteins surrounding Animal cells Binds cells together in tissues Has protective and supportive functions Regulates cell behavior AN EXTRACELLULAR MATRIX SURROUNDING A CELL FIGURE 10

7. Communication Four main kinds of communication -ENDOCRINE: FROM FAR AWAY -PARACRINE: LOCALIZED -AUTOCRINE: SELF -JUXTACRINE: ADJACENT -Either a hydrophilic or hydrophobic signaling molecule is sent to a receptor in/on the cell -If hydrophilic, the molecule must find a receptor on the membrane -If hydrophobic, the molecule can diffuse across the membrane FIGURE 11

8. Extracellular composition Contains an mesh of biomolecules Composed of proteins and glycosaminoglycans Produced inside the cell (EXAMPLE OF A GLYCOSAMINOGLYCAN)  ATTACHES TO EXTRACELLULAR JUNCTIONS  TIGHT JUNCTION: TWO CELLS HELD CLOSELY TOGETHER BY JOINED MEMBRANES  GAP JUNCTIONS: CHANNELS THAT ALLOW MOLECULE TRANSPORT  ADHERENS JUNCTIONS: MECHANICAL ATTACHMENT BETWEEN TWO CELLS  DESMOSOMES: BIND TWO CELLS TOGETHER. HELPS RESIST SHEARING FORCES FIGURE 12

9. Purposes of the extracellular matrix Provide structural support to animal cells Separates different tissues Regulates intercellular communication Attaches to cell junctions Allows the cells to attach to each other (EXTRACELLULAR MATRICES IN A TISSUE) FIGURE 13

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