Transport

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  • Transport
    • Facilitated Diffusion
      • Doesn't require energy
      • Uses transport proteins to move from high to low concentration
      • Examples - Glucose or amino acids moving from blood into a cell
      • Some carrier proteins do not extend through the membrane
      • They bod and drag molecules through the lipid bilayer and release them on the opposite side
      • Other carrier proteins change shape to move materials across the cell membrane
    • Active Transport
      • Requires energy of ATP
      • Moves materials from low to high concentration
      • Against concentration gradient
      • Examples - Pumping Na+ out and K+ in against strong concentration gradient
        • Called Na+-K+ pump
        • 3 Na+ pumped in for every 2 K+ pumped out; creates a membrane potential
      • Large molecules move into the cell by one of those two forms of endocytosis
        • Pinocytosis - most common form of endocytosis. Takes in dissolved molecules as a vesicle
        • Exocytosis - molecules are moved out of the cell by vesicles that fuse with the plasma mebrane
        • This is how many hormones are secreted out and has nerve cells communicate with one another
        • The opposite of endocytosis is exocytosis
          • Exocytosis - molecules are moved out of the cell by vesicles that fuse with the plasma mebrane
    • Small molecules and larger hydrophobic lipid soluble molecules move through easily e.g. O2, H2O, CO2
    • Cholesterol = Stablity
      • Less fluid at high temperatures
      • More fluid at low temperatures
    • Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own
    • Proteins are critical to membrane function:
      • Structural support - cholesterol
      • Recognition - glycolipid
      • Communication - glycoprotein
      • Transport - channel protein
    • Channel proteins are embedded in the cell membrane  have a pore for materials to cross
    • Carrier proteins can change shape to move material from one side of the membrane to the other

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