plasma membranes

• compartentalisation- the formation of separate membrane bound areas in a cell
• intrinsic proteins

  channel proteins- allow passive movements of polar molecules and ions

  carrier proteins- both passive and active transport, changes shape of protein
• glycoproteins

  • cell signalling receptor for neurotransmitter
  • drugs
• extrinsic proteins

  • present on one side of bilayer
  • hydrophilic R-group on outer surface
• cholesterol

  • regulates fluidity
  • adds to stability
• glycolipids

  • antigens
  • recognised by immune system
• temperature affects membrane structure

  • as temperature increases, phospholipids have more kinetic energy so will move more
  • membrane more fluid
  • creates gaps within the structure making it more permeable
  • carrier and channel proteins denatured at higher temperatures
• solvents affect membrane structure

  • organic solvents will dissolve membranes, disrupting cells

  Anticeptic wipes- alcohols dissolve membranes of bacteria (killing them)

  Alcoholic drink- when neuronal membrane is disrupted, nerve impulses are no longer transmitted as normal, this causes a change in the persons behaviour
• water potential- pressure exerted by water molecules as they collide with a membrane
• pure water- 0 pa

  more concentrated solution- negative pa
• cytrolysis

  • if solution has a higher water potential than cell cytoplasm, water will move into cell by osmosis
  • hydrostatic pressure in the cell will build up, the cell will burst
• crenation

  • if solution has a lower water potential than cell cytoplasm, cell will loose water by osmosis
  • cell volume decreases and the cell puckers
• pressure against cell wall- turgor (cell becomes turgid)

  membrane pulled away from wall- plasmolysed
• diffusion- net movements of particles from an area of high concentration to an area of low concentration via a concentration gradient
• factors affecting rate of diffusion

  • temperature
  • surface area
  • concentration gradient
  • membrane thickness
• facilitated diffusion

  • phospholipid bilayers are barriers to polar molecules and ions
  • the more protein channels, higher the rates of diffusion

  channel proteins- polar molecules/ ions pass through

  carrier proteins- change shape of molecule
• active transport

  1. molecule being transported bind to receptors in the channel of the carrier protein
  2. once on the inside ATP binds to the carrier protein and is hydrolysed into ADP and phosphate
  3. binding causes the protein to change shape. It opens up the to inside of the cell and the ion is released.
  4. recombines to form ATP and the carrier protein returns to original shape
• Bulk transport

  • form of active transport where molecules are too large to move through channel/ carrier proteins
• endocytosis

  -material entering cells

  (phagocytosis- solids)

  (pinocytosis- liquids)

  1. cell surface membrane bends inwards
  2. membrane enfolds until becomes a vesicle
  3. vesicle pinches off and moves into the cytoplasm
• exocytosis

  -material exiting the cell

  1. vesicle formed by golgi apparatus
  2. vesicle moves towards and fuses with cell membrane
  3. contents are released outside of the cell