Factors Affecting Membrane Structure and Permeability

  • Created by: Freja
  • Created on: 13-04-21 11:57
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  • Factors Affecting Membrane Structure and Permeability
    • Temperature
      • Increase in kinetic energy of the phospho-lipids. So the membrane becomes more fluid and disrupts the structure of the membrane.
        • This created more gaps in the membrane, so it becomes more permeable so more particles can cross into the cell more easily.
      • Temperatures below 0C- The phospholipids don't have much energy, so they can't move much. They're packed closely together and the membrane is rigid. But the channel and carrier proteins in the membrane deform, increasing the permeability of the membrane. Ice crystals may form and pierce the membrane making it highly permeable when it thaws.
      • Temperatures between 0C and 45C- The phospholipids can move around and aren't packed as tighly together, so the membrane is partially permeable. As the temperature increases the phospholipids move more because they have more energy, which increases the permeability of the membrane.
      • Temperatures above 45C- The phospholipid bilayer starts to melt and the membrane becomes more permeable. Water inside the cell expands, putting pressure on the membrane. Channel and carrier proteins deform so they can't control what enters or leaves the cell, increasing the permeability of the membrane.
    • Solvents
      • Surrounding cells in a solvent increasing the permeability of the plasma membranes.
      • The solvents dissolve the lipids in a cell membrane, so the membrane loses its structure.
      • Some solvents increase permeability more, e.g. ethanol increases the cell permeability more than methanol.
      • Increasing the concentration of the solvent will also increase the membrane permeability.
      • Non-polar alcohol molecules can enter the phospholipid membrane and the presence of these molecules between the phospholipids disrupts the membrane.
    • pH
      • The pH affects the protein structure.
      • The low pH means it is more acidic, so there are more H+ ions. The H+ ions disrupt the hydrogen bonds in proteins, which affects the tertiary structure.
    • It is important to maintain fluidity, otherwise the cell would not be able to function.
    • Needed for : diffusion of substances across the membrane, membranes to fuse and for cells to move and change shape.
    • The Solvent Water
      • Water is a polar molecule, which creates stability within the bilayer membrane, as it does not disrupt the membrane, as the phospholipids will not dissolve in water.


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