Cell Membranes

View mindmap
  • Cell Membranes
    • Roles of membranes
      • Separating cell contents from the outside environment
      • Separating cell components from cytoplasm
      • Cell recognition and signalling
      • Holding the components of some metabolic pathways in place
      • Regulating the transport of materials into or out of cells
    • Phosphlipid  bilayer
      • Phosphate  'head'
        • Hydrophilic -water loving
        • Phosphate head stick into the water
      • Fatty acid (lipid) 'tail'
        • Hydrophobic - water hating
      • If phosholipid molecules are completely surrounded by water, a bilayer can form.
        • Phosphate heads on each side of the bilayer stick into the water, while the hydrophobic fatty acid tails point towards each other
          • Means that the hydrophobic tails are away from water
          • Phospholipid molecules can move freely -  just like fluid molecules do.
          • Gives the bilayer stability
      • Basic structural component of all biological membranes
        • Hydrophobic layer formed by the phosphlipid tails creates a barrier to many molecules and separates the cell contents from the outside world.
      • Differentiation of membranes
        • Phosphlipid bilayer would be to fragile to function as a barrier without other components
        • Examples
          • Plasma membranes of the cells in a growing shoot contain receptors the molecules that regulate growth
          • Muscle cell membranes contain a large number of channels that allow rapid uptake of glucose
    • The fluid mosaic model
      • Used to describe the molecular arrangemnts in membranes.
      • Feature: a bilayer of phospholipid molecules forming the basic structure
      • Feature: various protein molecules floating in the phospholipid bilayer, some completly freely, some bound to other components or to sturctures within the cell
      • Feature: some proteins partially embedded in the bilayer on the inside or the outside face;other protiens completely spanning the bilayer
    • Glycoproteins and glycolipids
      • Where phosphlipid molecules have a carbohydrate part attached they are called glycolipids
      • Where protein molecules have a carbohdrate part attached they are called glycoproteins
    • Membrane components and their roles
      • Membranes stability and fluidity
        • Cholesterol gives the membranes some mechanical stability. Fits between the lipid tails and makes the barrier more complete
      • Membrane transport functions
        • Channel proteins allow the movement of large/charged substances across the membrane.
        • Carrier proteins actively move large/charged substances across the membrane
      • Recognition and communication
        • Receptor sites - some allow hormones to bind with the cell so that a cell 'response' can be carried out. A cell can respond to a hormone only if it has a receptorfor that hormone on its cell surface membrane
        • Glycoproteins/lipids are involved in cell signalling that they are 'self' to allow recognition to by the immune system
    • Temperature
      • Increasing temperature gives molecules more kinetic energy - they will move faster.
        • Increased movement of phospholipids and other components makes membranes leaky
          • Allows subsutances that would normally not do so to enter or leave the cell.
      • Organisms that live in very hot or very cold environments need differntly adapted molecular components of their membranes so that their membranes can perform the functions needed to maintain life


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Cellular processes and structure resources »