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Transport across cell membranes (DIFFUSION (Definition (A net movement of…

- - - - Is hydrophillic
      - Point to the outside of the cell membrane attracted by water on both sides.
    - - 2 fatty acids which made of hydrocarbons
      - Phosphate
      - Gycerol
    - - Is hydrophobic
      - Point into the center of the membrane repelled by water on both sides.
    - - Whats allowed through the cell through the phospholipids?
        
        Allowed substances that can enter and leave the cell.
        
        small, uncharged, lipid soluble.
        
        Not allowed/prevented substances from entering or leaving the cell.
        
        large, charged, water soluble.
      - Make the membrane flexible and self-sealing.
  - - - 1) Some proteins occurs in the surface of the bilayer and never extend completely across it. They act either to give mechanical support to the membrane or, in conjunction with glycolipids , as cell receptors for molecules such as hormones.
      - 2) Other proteins span across the phospholipid bilayer from one side to the other. Some are protein channels, which form water-filled tubes to allow water-soluble ions to diffuse across the membrane. Others are carrier proteins that bind to ions or molecules like glucose and amino acids, then change shape in order to move these molecules across the membrane.
    - - Form cell-surface receptors for identifying cells
        
        ligand-gated ion channels
        
        Ligand-gated ion channels (LICs, LGIC), also commonly referred to as ionotropic receptors, are a group of transmembrane ion-channel proteins which open to allow ions such as Na+, K+, Ca2+, and/or Cl− to pass through the membrane in response to the binding of a chemical messenger (i.e. a ligand)such as a neurotransmitter.
        
        G protein-coupled receptors
        
        receptor tyrosine kinases.
      - 3) Allow active transport across the membrane through carrier proteins.
      - Help cells adhere (Stick fast) together.
      - 2) Act as channels transporting water soluble substances across the membrane.
      - Act as receptors, e.g. hormones.
      - 1) Provide structural support