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biological membranes (cell membranes (cell membrane receptors (drugs bind…

- - - - barrier between cell and its environment controlling which substances enter or leave the cell
      - partially permeable
      - substances move across by osmosis, diffusion and active transport
      - they allow RECOGNITION by other cells e.g. cells of immune system
      - they allow RECOGNITION by other cells e.g. the cells of immune system
      - they allow CELL COMMUNICATION (cell signaling)
    - - membranes around organelles divide cell into different compartments - act as a barrier between organelle and cytoplasm(makes functions more efficient)
      - can form vesicles to transport substances between different parts of cell
      - control which substances enter or leave the organelle
      - partially permeable
      - membranes within a cell can be a site of chemical reactions e.g. the inner membrane of mitochondria contains enzymes needed for respiration
  - - - form a barrier to dissolved substances
      - head is hydrophillic and tail is hydrophobic
      - molecules automatically arrange themselves into bilayer - heads face out towards water on either side of membrane
      - centre of bilayer is hydrophobic so the membrane DOESNT allow water-soluble substances (e.g. ions) through it (acting as a barrier) but fat soluble substances can dissolve in bilayer and pass through
    - - gives the membrane STABILITY
      - cholesterol is a type of LIPID
      - present in ALL CELL MEMBRANES except bacterial
      - cholesterol molecules fit between phospholipids and BIND to hydrophobic tails causing them to pack more closely together- makes membrane less fluid and more rigid
    - - protein channels in membrane allow small or charged particles through e.g. ions
      - protein carriers transport molecules and ions across membrane by ACTIVE TRANSPORT and FACILITATED DIFFUSION
      - proteins also act as RECEPTORS for molecules e.g. hormones in cell signaling - when a molecule binds to a protein a chemical reaction is triggered inside cell
    - - act as receptors for messenger molecules in cell signalling
      - stabilize the membrane by forming hydrogen bonds with surrounding water molecules
      - sites where drugs, hormones and antibodies bind
      - act as antigens -involved in immune response
  - - - 1) one cell releases a messenger molecule (e.g. hormone)
      - 2) this molecule travels (e.g. via the blood) to another cell
      - 3) the messenger molecule is detected by the cell because it binds to a receptor on its cell membrane
  - - - bind to receptors
      - trigger a response or block the receptor and prevent it from working
  - - - 1) cut 5 equal sized pieces of beetroot and rinse them to remove any pigement released during cutting
      - 2) place the five pieces in five different test tubes with 5cm3 of water
      - 3) place each test tube in a water bath at a different temp for 15 minutes
      - 4) remove the pieces of beetroot from the test tubes leaving the coloured liquid
      - 5) use a COLORIMETER- the higher the permeability of the membrane, the more pigment is released and the higher the absorbance of the liquid
  - - - phospholipids don't have much energy so don't move alot
      - packed close together and membrane is rigid
      - BUT channel and carrier proteins can deform/denature which increases permeability
      - ice crystals may form and pierce membrane increasing permeability
    - - phospholipids can move and are not as closely packed- the membrane is partially permeable
      - as temp increases phospholipids move more because they have more energy (increasing permeability)
    - - phospholipid bilayer starts to melt and membrane becomes more permeable
      - water inside cell expands putting pressure on membrane
      - channel and carrier proteins deform increasing permeability
  - - - solvents dissolve the lipids in cell membrane so it loses its structure
- - - - diffusion= the net movement of particles from an area of high conc to an area of low conc- down the conc gradient
      - molecules will diffuse both ways but the net movement will be to the lower conc - continues until particles are evenly distributed
      - concentration gradient= path from an area of higher concentration to an area of low concentration - particles diffuse down
    - - small, non polar molecules e.g. oxygen and carbon dioxide are able to diffuse easily through spaces between phospholipids
      - water diffuses across membrane by osmosis because it is small despite being polar
    - - concentration gradient- higher it is, the faster the rate
      - thickness of exchange surface- the thinner the exchange surface, the faster the rate
      - surface area- the larger the surface area, the faster the rate
      - temperature- the warmer it is, the faster the rate (particles have more kinetic energy to move faster)
    - - 1) make up agar jelly with phenolphthalein and dilute sodium hydroxide - turning it pink
      - 2) fill beaker with dilute hydrochloric acid and using a scalpel cut out a few cubes from jelly and put in beaker of acid
      - 3) eventually cubes turn colorless as acid diffuses into agar jelly and neutralizes sodium hydroxide
      - surface area
        
        cut agar jelly into different sized cubes and work out surface area to volume ratio and time how long cubes take to go colorless
        
        larger surface area to volume ratio, faster it will turn colourless
      - conc gradient
        
        use different concs of hydrochloric acid and keep size of agar cubes the same and time how long they take to go colourless
        
        high conc, faster it will turn colourless
      - temp
        
        put boiling tubes of HCl in waterbaths at different temps and put equal sized agar cubes in and time how long it takes to go colourless
        
        higher the temp, the faster it will go colourless
    - - osmosis= the diffusion of water molecules across a partially permeable membrane down the concentration gradient from an area of high water potential to an area of low water potential
      - water potential= the potential of water molecules to diffuse out of or into a solution
      - pure water has highest water potential, all other solutions are lower
  - - - large molecule attaches to a carrier protein in membrane
      - then protein changes shape
      - this releases molecule on opposite side of membrane
    - - form pores in the membrane for charged particles to diffuse through
      - different channel proteins facilitate the diffusion of different charged particles
  - - - taking in large solid material
      - cell membrane forms pseudopods which surround material to be taken into cell
      - the pseudopods fuse together around material, fully enclosing it within vesicle
      - vesicle is transported inside cell
    - - small sized particles are taken in
      - vesicles formed by cell membrane WITHOUT formation of pseudopods
  - - - hypotonic solution (solution with higher water potential) = net movement of water into cell- cell bursts
      - isotonic solution(same water potential in cell)= water passes in and out in equal amounts- cell stays the same
      - hypertonic(solution with lower water potential)= net movement of water molecules is out of cell - cell shrinks
    - - hypotonic solution= net movement of water into cell- vacuole swells and cell becomes TURGID
      - isotonic solution= water molecules move in and out of cell in equal amounts- cell stays same
      - hypertonic solution= net movement of water molecules out of cell- cell becomes flaccid (cytoplasm and membrane pull away from cell wall- plasmolysis)