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Spring 2010 chapter 3a PowerPoint for BIOL2401 (Human Anatomy & Physiology) at San Antonio College with Alba

Spring 2010 chapter 3a PowerPoint for BIOL2401 (Human Anatomy & Physiology) at San Antonio College with Alba



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    Chapter3a Chapter3a Presentation Transcript

    • Chapter 3: Cells: The Living Units
    • The Cellular Basis of Life: Cell Theory
      • A cell is the basic structural & functional unit of living organisms
      • The activity of an organism depends both the individual & collective activity of its cells
      • Biochemical activities of cells are dictated by the relative number of their specific subcellular structures
      • Continuity of life has a cellular basis
    • Cell Diversity
    • The Composite Cell
    • The Plasma Membrane: Structure
      • Very thin, s electively permeable phospholipid bilayer
      • Membrane proteins: surface receptors, pumps, channels, cytoskeletal anchors
      • Membrane carbohydrates- Cell recognition, “ID tags”
    • The Plasma Membrane: Functions
      • Defines the cell’s boundary
      • Selectively permeable membrane that transports substances in and out of the cell
      • Generates and maintains the resting membrane potential
      • Mediates cell-cell and cell-environment interactions
    • Transport: Protein channels and pumps transport specific substances into the cell Enzymatic Activity: Some enzymes are at the membrane, supplying products where they are needed Signal Transduction: Some membrane proteins are receptors that receive external signals and initiate cascades of chemical reactions
    • Intercellular Joining: Cell adhesion molecules (CAMS) provide binding sites for cell-cell interactions Cell-Cell Recognition: Some glycoproteins serve as cellular “ID” tags that allow cells to recognize each other Attachment to the cytoskeleton and ECM: Some membrane proteins act as anchors for the cell, binding the cell to its environment and supporting the cytoskeleton
    • Plasma Membrane Special Structures
    • Special Structures: Tight Junctions
      • Interlocking junctional proteins fused together to form a relatively impermeable barrier around cells
      • Prevents molecules from passing between adjacent cells
      • Example: Digestive tract lining to prevent “seeping”
    • Special Structures: Desmosomes
      • Plaque & linker proteins interdigitate like a zipper
      • Allow for cell sheets to form
      • Also prevents cell sheets subjected to mechanical stress from tearing
      • Examples: Skin, heart muscle
    • Special Structures: Gap Junctions
      • Communicating junction between cells
      • Connexons are transmembrane proteins that form channels that span across adjacent cells
      • Essential for excitable tissue that require rapid communication in order to synchronize activities
      • Examples: Cardiac & smooth muscle
    • Membrane Transport
      • Cells are surrounded by extracellular fluid/ interstitial fluid containing nutrients, amino acids, sugars, fatty acids, vitamins, etc.
      • Cells need to extract essential substances from interstitial fluid in order to survive
      • Traffic across the plasma membrane is constant but is also selective on what substances are introduced into the cell
      • Transport is either passive or active
    • Membrane Transport
      • Passive Processes
        • Diffusion
          • Simple Diffusion
          • Facilitated Diffusion (channel & carrier-mediated)
          • Osmosis
        • Filtration
      • Active Processes
        • Active Transport
        • Vesicular Transport
    • Diffusion
      • The tendency of molecules or ions to scatter evenly throughout the environment
      • Molecules and ions move down their concentration gradients until equilibrium is reached
      • [High]  [Low]
    • Diffusion
      • Molecules diffuse through the membrane if:
      • Lipid-soluble
      • Small
      • Assisted by a carrier molecule
      • Types of Diffusion:
      • Simple Diffusion: Unassisted diffusion
      • Facilitated Diffusion: Assisted diffusion
        • Channel-mediated
        • Carrier-mediated
      • 3) Osmosis: Diffusion of solvents (water)
    • Simple Diffusion
      • Small, non-polar, lipid-soluble substances diffuse directly through the lipid bilayer from regions of high concentration to low concentration
      • Examples: Oxygen, Carbon dioxide, fat-soluble vitamins
    • Channel-Mediated Facilitated Diffusion
      • Protein channels form “tunnels” that allow small, lipid-insoluble molecules (water, ions) into the cell
      • Channels are selective, only allowing molecules of certain sizes and charges to pass through
    • Carrier-Mediated Facilitated Diffusion
      • Large, polar, lipid-insoluble molecules such as sugars and amino acids bind to protein carriers and are “shuttled” across the membrane
      • Carrier membrane proteins are molecule-specific
    • Osmosis
      • Specific to the movement of water (a solvent) through a membrane from regions of high water concentrations to regions of low water concentrations
      • Osmotic diffusion of water may be directly through the lipid bilayer or through aquaporins
    • Diffusion –vs- Osmosis
    • Tonicity Hypertonic: Osmotic pressure outside the cell is higher, water leaves cell faster than it enters Isotonic: Osmotic pressure in and out of cell are equal, water enters and leaves cell at same rate Hypotonic: Osmotic pressure inside cell the higher, water enters the cell faster than it leaves
    • Filtration
      • Movement of molecules through membranes from regions of high hydrostatic pressure to regions of lower hydrostatic pressure
      • Separation of solids from fluids
      • Generally applies only to capillary walls