Cell membrane (WIP) --> Add Co-Transport, use example and add diagrams

Cell membrane (WIP) --> Add Co-Transport, use example and add diagrams

1. Membrane

   • Components
     • Phospholipid Bilayer
       • Phosphate head - Hydrophilic
         • Face outwards, and towards the watery environment surrounding and inside the cell
       • Fatty acid tails - Hydrophobic
         • Point inwards
         • Prevent water soluble molecules entering the cell
         • Prevent soluble polar molecules leaving the cell
       • Allows these molecules to pass through:
         • Non-polar molcules
         • Small molecules
         • Lipid soluble molecules
     • Proteins
       • Extrinsic
         • Cell-receptors
       • Intrinsic/Integral
         • Protein channels
           • Form channels and allow one type of molecule to pass through
           • Water filled hydrophilic
         • Carrier proteins
           • Bind ions and changes shape to allow molecules to pass
             • Complementary shape
           • Use ATP
             • Binds to protein and becomes ADP, changing its shape
           • Three types
             • Uniport - Transports one type of ion in one direction
             • Antiport - Requires two types of ions, moving in different directions
             • Symport - Requires two tpes of ions, moving in the same direction
               • Example: Sodium ion enters a symport, pulls a glucose molecule with it against the concentration gradient (Indirect active transport)
       • Other functions:
         • Structural support
         • Help cells adhere together
     • Cholesterol
       • Structural strength
       • Hydrophobic (Prevents water loss)
       • Prevent phospholipid moving away from each other or colliding
       • Makes membrane less fluid at high temperatures
     • Glycolipds
       • Recognition sites
       • Help cells attach to each other
       • Maintain stability
     • Glycoproteins
       • Aids in cell recognition
       • Recognition sites
       • Helps cells attach to each other
   • Partially Permeable
   • Creates different environments outside and inside of the cell
   • Controls movement of substances in and out of the cell

2. Fluid Mosaic Model

   • Cholesterol present to stabilise
   • Proteins are scattered
   • Phospholipid move relative to each other

3. Transport

   • Diffusion
     • Simple diffusion
       • Molecules pass through the membrane
       • Molecules
         • Small
         • Non-polar
         • Lipids
     • Fracilitated diffusion
       • Molecules pass through channel proteins
       • Molecules
         • Water soluble
         • Polar
         • Large
     • Affected by
       • Surface area
       • Temperature
       • Diffusion pathway
       • Concentration gradient
       • Molecules size
       • Lipid solubility
   • Osmosis
     • Water potential
     • Measured in Psi
       • Solute Potential - Effects on solutes lowering the Psi of cell sap
         • Negative value
       • Pressure Potential - Tendency of water to leave cell, opposite pressure generated
         • Positive value
     • High water potential --> Low water potential
     • Solutions
       • Isotonic - Solution with equal concentration to the cell
         • Movement of water, no new movement
           • Plant cell - Flacid
           • Animal cell - Normal
       • Hypotonic - Solution with higher concentration of water than the cell
         • Net movement into the cell
           • Animal cell --> Lysing (Burst)
           • Plant cell - Turgid
       • Hypertonic - Solution with lower concentration of water than the cell
         • Net movement out of the cell
           • Animal cell - Shrivelled
           • Plant cell - Plasmolyses (Shrink)
   • Active transport
     • Against the concentration gradient
     • Need ATP
   • Endocytosis/Exocytosis
     • Endocytosis - Movement of large materials in bulk into a cell
       • Phagocytosis - Cells obtain solid particles too big for diffusion or active transport
         • Invaginates then buds off to form a phagosome, lysosomes digest contents
         • Pincocytosis - Intake of liquids
     • Exocytosis - Secreting material in bulk, transport by vesicle