Biology 1020 lecture 8 Cell structure 3

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  1. Eukaryotic cell structure: support elements within the cell
    • - Pressure from fluid (vacuole)
    • - Cytoskeleton
  2. Eukaryotic cell structure: Cytoskeleton
    • Network of fibers extending throughout the cytoplasm (its dynamic)
    • Anchors many organelles, supports cell and maintains shape
    • Regulate biochemical activities
  3. Cytoskeleton
    Some organelles and vesicles move along the cytoskeleton: Motor proteins produce motility. -- Web like structures "acts as a highway"
  4. Cytoskeleton: Classified based on diameter
    • Microfilaments (actin, myosin filaments) - thinnest
    • Intermediate filaments - middle range
    • Microtubules - Thickest
  5. Microfilaments #1
    • Solid rods
    • Twisted double chain of actin subunits (nanometer range)
    • Near plasma membrane => cortex
    • Anchored -->minus end
    • Growing end --> plus end
    • Can resist pulling/bear tension
    • Moves organelles, change cell shape
  6. Microfilaments #2
    • Different functions/shapes
    • - Microvilli
    • - Cytoplasmic contractile bundles
    • - Lamillipodia and filipodia
    • - Cell division contractile ring
  7. Microfilaments
    Cytoplasmic streaming: Myosin moves organelles on a bed of actin (think of the moving chloroplasts)

    - Myosin and actin filaments move past each other to shorten the muscle cell.

    - Actin and myosin polymerize to form pseudopodium in amoeboid movement
  8. Intermediate Filaments
    • Support cell shape and fix organelles in place. ex. nuclear lamina
    • Do not polymerize and depolymerize very quickly - more permanent
    • ex. keratin proteins
  9. Microtubules
    • Hollow rods of tubulin
    • Maintains cell shape, movement of cells, organelles and chromosomes
    • Plus and minus ends
    • - Grow by polymerizing tubulin at the plus end
    • - In animals - start growing centrosome (near nucleus). => minus end is anchored
    • - In plants - grows from microtubule organizing centre (MOC)
  10. Microtubules: Cilia and Flagella
    • Specialized for beating
    • * Cilia: power stroke and recovery stroke
    • Can move liquid or air past a cell, or move the cell itself
    • They have a core of mocrotubules surrounded by the plasma membrane

    • Consists:
    • - Outer microtubule doublet
    • - Plasma membranes
    • - Dynein proteins
  11. Microtubules: Cilium
    • - Anchored with basal body --> cell membrance
    • - 9 groupings of 2 microtubules => doublets
    • - 2 of each basal body doublets extend out into cilium. Cilium - doublets
    • - Additional pair in the middle (independently)

    • Note: Cross section of basal body (similar in structure to centriole). Has 9 triplet microtubules groups arranged in a kind of pinwheel design.
    • 9 doubles
    • 2 singles
    • 9 + 2 structure
  12. Microtubules: Cilia and flagella (cilium)
    • Structure of cilia and flagella is a similar in many eukaryotes (paramecium and cells of windpipe cells)
    • Motor protein - called DYNEIN - bends cilium
    • Dynein anchored in doublet of tubules
    •  * Arms grab and move along another doublet (outer)
    • Protein cross-links, limit sliding
    • Cause doublets to curve, bending the cilium or flagellum
  13. Cytoskeleton: Multiple fibres in one cell type
    • Intestinal microvilli
    • - Microfilaments reinforce the microvilli, anchored to intermediate filaments
  14. Eukaryotic cell structure: connections of cells within tissues.
    • Materials that are external to the plasma membrane
    • Synthesized and secreted by the cell
    • Connected to cytoskeleton via membrane proteins
  15. Extracellular matrix (ECM) Multicellular organism
    • Network of material
    • Secreted to outside of cell (sometimes in large amounts)
    • Strong ex. animal skin
    • Hold cells of a tissue together
    • Provides support
    • Cell signalling
    • Fluid --> extracellular fluid
    • Plants - cell wall
    • Animals - glycoproteins (from rough ER) (collagen) in proteoglycan
  16. Parts of extracellular matrix
    • - Extracellukar fluid
    • - Collagen (the thickest strand)
    • - The proteoglycan complex (look like the long thin branches that weave around the collagen)
    • - The Fibronectin attached to the collagen on one end, and to the other the integrin
  17. ECM: Proteoglycan complex
    • The main branch consists of a polysaccharide
    • A side branch (proteoglycan molecule), the core is a protein, the little off shoots are carbohydrates
  18. ECM: Signalling
    Collagen --> Fibronectin --> integrins --> cytoskeleton (microfilaments)
  19. Form and function in animal cell junctions
    • 1. Prevent leakage (like skin): The plasma membrane of adjacent cells in close connection. This is done through specific proteins. Results ina continuous seal.
    • => Tight junction

    • 2. Join in strong sheets (like muscle cells): The intermediate filaments extend far into the cell.
    • => Desmusomes/Anchoring

    • 3. Chemical communication among cells in a tissue (intestinal cells): Membrane proteins of adjacent cells come together to make a pore.
    • => Gap junction
  20. Plant ECM: Cell wall
    • Cellulose micro fibres embedded in other polysaccharides and protein matrix
    • Thin layer of polysaccharide (pectin) between primary walls of adjacent cells (middle lamella)
  21. Form and function in plant cell junctions
    • Cytoplasm of one cell continuous with another through plasmodesmata (small passage way through the cell walls)
    • Water, small solutes, some proteins can pass through, move along cytoskeleton
  22. Cell structure and function
    • High rates of protein synthesis --> Fibosomes/nucleoli
    • Movement --> cilia/flagella
    • Energy consumption --> mitochondria
    • Detoxification --> peroxisomes
    • High turnover --> Lysosomes
    • Storage: Vacuoles
    • Steroid hormone production: Smooth ER
  23. Separating organelles for study: Fractionation
    • Collect the tissue
    • Homogenize: break up the cells - forms a homogenate
    • Differential centrifugation (multiple steps): Cell components will fall to the bottom of the tube at speeds dependent on their size and mass
    • Larger, heavier items form pellets at lower speeds
    • Centrifuge each supernatant (the liquid on top of the debris in the tube) at a higher speed
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Biology 1020 lecture 8 Cell structure 3
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