Cell Membranes - Parts and Roles II

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  • Created by: Vikki4
  • Created on: 08-03-15 15:50
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  • Cell Membranes
    • Phospholipids
      • Short chain fatty acids increase fluidity
      • Fluid barrier
      • Unsaturated fatty acids also increase membrane fluidity (especially cis)
      • Does not allow water soluble or polar molecules through easily due to its hydrophobic core
      • Allow fluidity
        • Membrane fusion
        • Vesicle formation
    • Glycolipids
      • Have high specificity
      • Involved in cell cell recognition
    • Cholesterol
      • Steroid
      • Mechanically stabilises the membrane
      • Reduces leakage of polar molecules
      • Regulates membrane fluidity
    • Roles of the structures
      • Allow membrane to be partially permeable
        • Proteins and glycoproteins
          • Receptors for hormones and neurotransmitters
          • Involved in cell cell recognition
          • Are enzymes (microvilli)
          • Channels and carrier proteins
          • Involved in energy tranfser reatcions in respiration and photosynthesis
          • Have high specificities
      • Allow fluidity
        • Membrane fusion
        • Vesicle formation
      • Selective cell cell recognition
        • Glycolipids
          • Have high specificity
          • Involved in cell cell recognition
        • Proteins and glycoproteins
          • Receptors for hormones and neurotransmitters
          • Involved in cell cell recognition
          • Are enzymes (microvilli)
          • Channels and carrier proteins
          • Involved in energy tranfser reatcions in respiration and photosynthesis
          • Have high specificities
      • Separate cell contents and allow compartmentalisation
    • Membrane fludidty
      • Classic experiment to prove
        • Cell with plasma membrane proteins green fluorescence
          • Shocked cells to fuse
            • Expected half green half red if proteins rigid
            • Actually got random mixtures of proteins, proving they could move and membranes are fluid
        • Cell with plasma membrane proteins red fluorescence
          • Shocked cells to fuse
            • Expected half green half red if proteins rigid
            • Actually got random mixtures of proteins, proving they could move and membranes are fluid
      • Effect of changing tempreature
        • Increased movement of phospholipids makes membranes leak
        • Increased temperature gives molecules more kinetic energy
          • For beetroot this means the betalain will diffuse more quickly
        • Denaturation of proteins makes membranes leak
        • At high temperatures, denatured proteins can reblock gaps in the membrane
        • Extremophiles have different membrane compositions (cholesterol and different fatty acid chain lengths)
    • Roles in cell signalling
      • Communication and coordination between cells
      • Specific substance released by one cell and binding to specific receptor on another cell to create a response
        • Signal and receptor are complementary
        • Drugs work by having same shapes as signalling molecules
      • Examples
        • Neurotransmitters
        • Hormoes released into the blood
          • Adrenaline binds to liver cells to stimulate breakdown of glycogen
          • Made by endocrine glands
          • Diffuse from blood to target cell receptors or cytoplasm
        • Local cell mediators (short distances)
          • Cytokines in immune response
          • Only in immediate environment
          • Taken up by cells or rapidly destroyed

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