S t r u c t u r e   &   O r g a n i z a t i o n :     L e c t u r e  # 7 Vocabulary | Study Questions
Cells: Movements of Materials
Objectives:
  1. Understand the processes and purposes of diffusion and osmosis.
  2. Understand the following biological mechanisms:
    1. facilitated diffusion
    2. active transport
    3. endocytosis
    4. exocytosis
  1. Water potential and the movement of water and solutes
    Water potential is the ability of water to move from an area of higher concentration (more energy) to an area of lower concentration (less energy). With molecules, the higher the concentration, the higher the energy.
    'Moving along a concentration gradient' means moving from an area of higher concentration to a lower one.
    1. Factors affecting water potential
      1. Gravity
        Energy of position. (Used in our obtaining electricity.)
      2. Pressure
        Helps to maintain the cell shape (e.g. the vacuole in a plant cell). Pressure can push water, but only so far: other kinds of forces must come into play to move water up a tree, for example.
      3. Concentration of solute particles
        Solute is anything that is dissolved in a substance (such as water). The concentration of water to solute.
    2. Patterns and approaches to solute and water movement:
      1. Diffusion
        90% of movement of materials across cell membranes is by simple diffusion: movement from a lower to a higher concentration (Figure 7.1).
      2. Osmosis
        A special case of diffusion: the movement of WATER from a higher concentration to a lower concentration across a selectively permeable membrane. (3 aspects of the definition: water, higher to lower, semi-permeable membrane (Figure 7.2).) Note that this movement involves a water concentration gradient, not a solute concentration gradient (they are inversely related).
  2. Movement of materials across cell and organelle membranes
    Not all materials can be moved through the cell membrane by simple diffusion or osmosis: insulin, for example.
    1. Membrane structure
      (Review: phospholipid bilayer, proteins. Many materials cannot move through it: proteins and ions, for example.)
      1. Molecular composition of membranes
        Determines membrane permeability.
      2. Organization and structure of cell membranes
    2. Membrane function
      (In transportation)
      1. Metabolism
      2. Selective permeability
      3. Protein carriers and transport
        1. Facilitated diffusion
          Using a protein, materials are able to move, as in simple diffusion, from an area of higher to one of lower concentration (along the concentration gradient). (Example: glucose being moved into the cell. Glucose attaches to the protein embedded in the phospholipid bilayer. The protein then changes shape, allowing the glucose to enter the cell cytoplasm.) No ATP is involved! Figure 7.3: Movement of Materials
        2. Active transport
          Uses ATP (energy) to move materials across a cell membrane (using a protein carrier) AGAINST the concentration gradient (from a lower to a higher concentration). Example: on the outside of a cell there are potassium ions (from bananas) that need to be moved to the inside, which already contains a higher concentration of potassium ions. To move the ions from an area of higher to one of lower concentration requires energy: the ion attaches to an embedded protein outside of the cell; when ATP attaches to the protein on the inside of the cell (cytoplasm) its third phosphate bond is broken, releasing energy; using this energy, the shape of the protein changes (flips) so that the ion is moved to the inside of the cell, where it os released; when the ATP (Adenosine TRIphosphate) releases this energy, ADP (Adenosine DIphosphate) drops from the protein but the third phosphate remains bonded; then, when the energy in the bond between the attached phosphate and the protein is released (the bond is broken), the protein is energized into returning to its initial shape, ready to move another ion.
          Figure 7.3: Movement of Materials Active transport can move a variety of materials in and out of the cell, some proteins functioning to move more than one particular material.

          3. Review the TABLE.

        3. Endocytosis and Exocytosis
          Figure 7.5: Endocytosis
          Endocytosis involves the plasma membrane engulfing materials and moving them into the cell (e.g. the amoeba that engulfs the bacteria; a white blood cell engulfing bacteria (phagocytosis) to be broken down by the hydrolytic enzymes of a lysosome).

          4. Figure 7.6: Exocytosis
          Exocytosis involves the packaging and transporting of materials from the inside to the outside of the cell (the opposite of endocytosis). Exocytosis is how we move proteins, for example, from the cell, where they are built, to be used outside of the cell (insulin is moved from pancreas cells into the blood by way of exocytosis).