cell fractionisation

• what is cell fractionisation?

  when organelles of a cell are separated
• what is the usual order of mass of organelles? (heaviest to lightest)

  nucleichloroplastsmitochondrialysosomesendoplasmic reticulumribosomes
• what are the 3 main stages in cell fractionation?

  1. homogenisation

  2)filtration3) ultracentrifugation
• what is homogenisation?


  breaking up the cells.the sample is vibrated at high speeds or the cells are ground in a blender.this breaks up the plasma membrane and releases the organelles into the solution.the solution must be kept ice cold, isotonic and buffered to minimise risk of damage and improve chances of seeing organelles functioning normally
• what does keeping the solution ice cold do ?

  reduces enzyme activity so they dont break down and slows metabolic reactions
• why should you keep the solution isotonic?

  cells have same chemical concentration as cells to prevent damage that could be caused by osmosis
• why should the solution be buffered?

  minimize potential denaturing of proteins by maintaining the ph
• what is filtration?


  where the larger unwanted pieces are removed.the solution is filtered through a gauze to do this
• what happens in ultracentrifugation?

  cell fragment solution is poured into a tube and placed in a centrifuge. it is spun at a low speed.heaviest organelles are forced to the bottom forming a thick sediment called a pellet. the other organelles are suspended in the liquid above called the supernatant.the supernatant is poured off and put into another tubethis process continues at increasing speed.