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    The Living Cell The Living Cell Presentation Transcript

    • Chapter 4 THE LIVING CELL
    • The Cell
      • A. Surrounds all cells
      • 1. Also called the
      • Cell Membrane
      • 2. Shape and Protection
      • 3. Boundary
      • a. Semipermeable
      • b. Controls movement of
      • materials in and out
      • of cell
      4-1 PLASMA MEMBRANE cell membrane 7nm wide Nerve cell Nerve cell Gap between cells 437 000x TEM
      • B. Membrane Architecture
      • 1. Made up of PHOSPHOLIPIDS
      • a. Phosphorus Head
          • Polar
          • Hydrophilic – attracted to water
      • b. Lipid Tail
          • Nonpolar
          • Hydrophobic –
      • not attracted to water
      4-1 PLASMA MEMBRANE POLAR A Phospholipid NONPOLAR
    • Phospholipids are important structural components of cell membranes. Phospholipids are modified so that a phosphate group (PO4-) replaces one of the three fatty acids normally found on a lipid. The addition of this group makes a polar "head" and two nonpolar "tails".
      • 2. Phospholipid Bilayer
      • a . Phospholipids form
      • a bilayer
        • Double layer
        • Surrounds cell
        • Blocks most polar
      • molecules
      • b . Cell is a prisoner
      • of the bilayer
      INSIDE CELL OUTSIDE CELL
    • Phospholipid Bilayer POLAR NONPOLAR POLAR Bilayer
      • c. Cholesterol binds to phospholipids
        • Makes membrane strong as well as flexible
        • Not present in all cells
      Remember the membrane is only 7 nm thick! cholesterol
    • OUTSIDE CELL INSIDE CELL 3. Embeded Proteins in Bilayer
    • Movement of selected molecules across the cell membrane
      • a. Channel Proteins
        • Selective Pathways
        • Called PORES or GATES
        • Allow polar and other certain molecules to pass
      • b . Receptor Proteins
        • Transfer Information
        • Examples
        • Insulin tells cell to
        • store sugar
        • Viruses match receptors
      • c . Marker Proteins
        • Tags
        • Identify cells
        • as “SELF”
        • and kind of cell
        • NONSELF are attacked by the immune system
      • Phospholipids and proteins float
      • Mosaic refers to the protein pattern
      • Flexible enough to fit any ce3ll
      4. Fluid Mosaic Model
    • Summary
      • Cell membranes have a basic structure composed of a PHOSPHOLIPID BILAYER.
      • Phospholipds have HYDROPHOBIC (non-polar) tails and HYDROPHILIC (polar) heads.
      • The best model of the cell membrane is called the FLUID MOSAIC MODEL
      • The average thickness of the membrane is 7nm.
      • The fatty acid tails of phospholipids can be SATURATED (straight) or UNSATURATED (bent)
      • Proteins can float or be fixed and also have hydrophobic and hydrophilic portions.
      • Some proteins and phospholipids have carbohydrates attached to them to form GLYCOPROTEINS AND GLYCOLIPIDS.
      • Phospholipids form the bilayer, act as barrier to most water soluble substances
      • Cholesterol regulates the fluidity of the membrane, gives mechanical stability and help to prevent ions from passing through the membrane.
      • Proteins act as transport proteins to act as channels for substances to move into or out of the cell. Some act as membrane enzymes and some have important roles in membranes of organelles.
      • Glycolipids and Glycoproteins help to stabilise membrane structure, some act as receptor molecules eg for hormones and neurotransmitters or as antigens for other cells to recognise them.
      • A. DIFFUSION
      • 1. Spreading out of substances
      • by random molecular motion
      • 2. Molecules from high to low
      • concentration
      • 3. DYNAMIC EQUILIBRIUM
      • a. Balance
      • b. Equal concentration on
      • both sides of cell
      • membrane reached
      • (materials in = out)
      4-2 MOVING IN AND OUT OF CELLS
    • Diffusion
      • B. OSMOSIS
      • 1. Diffusion of water across a cell membrane
      • 2. Osmotic Balance
      • a. Dynamic Equilibrium of water molecules
      • b. H 2 O entering the cell = H 2 O leaving the cell
      • 3. Osmotic Pressure
      • a. Results from water entering the cell
      • b. Could cause a cell to burst
          • RED BLOOD CELL PARAMECIUM
      • 4. Turgor Pressure
      • a. Water entering plant cell
      • pushes against cell
      • wall
      • b. Makes cell rigid
      • 5. Plasmolysis
      • a. Loss of H 2 O due to osmosis
      • b. Cell contents shrink
      • c. Causes plants to wilt
      • d. Prolonged plasmolysis
      • results in a cell’s death
      • e. EX. Salt as a weed killer
      • C. SELECTIVE TRANSPORT
      • 1. Movement through protein channels
      • 2. Channels are selective
      • 3. Types of Transport
      • a. PASSIVE TRANSPORT
          • Requires NO cellular energy
          • Movement in both directions
          • EX. Diffusion and Osmosis
      • FACILITATED DIFFUSION
          • Passive but channels assist movement
          • Molecules move down the concentration gradient
      • b. ACTIVE TRANSPORT
          • Requires cellular energy (pumps)
          • One directional against the concentration gradient
      • D. MOVING LARGE PARTICLES
      • 1. ENDOCYTOSIS
      • a. Moving materials IN
      • b. Cell membrane extends to engulf large particles
      • c. Types
      • PHAGOCYTOSIS
          • Takes in solids (White Blood Cells, Amoeba)
      • PINOCYTOSIS
          • Takes in liquids (Cell drinking)
      • RECEPTOR MEDIATED
      • 2. EXOCYTOSIS
      • a. Moving materials OUT
      • b. Cell releases materials from vesicles “sacs” at
      • membrane surface
      • A. PROKARYOTES
      • 1. NO Nucleus
      • 2. Bacteria divide by BINARY
      • FISSION
      • a. Circle of DNA (plasmid)
      • attached to membrane
      • b. DNA replicates
      • c. As cell elongates plasmids
      • separate
      • d. Cell divides into two
      • daughter cells
      4-3 HOW CELLS DIVIDE
      • B. EUKARYOTES
      • 1. Cells with a nucleus
      • a. More complex
      • b. DNA in chromosomes
      • 2. Mitosis and Cell Division
      • a. Characteristic of SOMATIC
      • CELLS (body cells)
      • b. MITOSIS
          • Chromosomes replicate and each daughter cell gets a complete set
          • Occurs in phases
      • c. CYTOKENISIS
          • Cytoplasm divides in half
          • Two daughter cells form