Cell fractionation

• What is cell fractionation?

  Cell fractionation is a process that separates different organelles within the cell using an ultracentrifuge, allowing them to be studied in detail.
• What are the 4 steps of cell fractionation?


  1. homogenise
  2. Filter
  3. prepare solution
  4. Ultracentrifugation
• What is homogenisation?


  Breaking open cells using a blender to release organelles into the solution
• Why is filtration a step during cell fractionation?


  Filtration removes larger cell debris or remaining tissue fragments (usually done through a gauze)
• What are the three properties of the solution cells should be kept in during cell fractionation?


  • Ice cold
  • Isotonic
  • Buffered
• why does the solution need to be ice cold during cell fractionation?


  to reduce enzyme activity and prevent breakdown of organelles
• why does the solution need to be isotonic during cell fractionation?


  Isotonic (ensures water potential is the same inside and outside the organelles) to prevent osmosis so organelles don’t shrivel or burst
• why does the solution need to be buffered during cell fractionation?


  it keeps the pH constant to prevent damage to enzymes and organelles
• what is ultracentrifugation?


  Ultracentrifugation is the process used to separate organelles based on their density by spinning filtered solution at various speeds to separate organelles
• Describe ultracentrifugation 


  1. Solution placed in a centrifuge and spun at low speed
  2. Heaviest organelle forms first pellet (nuclei) at the bottom of the tube
  3. Lighter organelles remain suspended in the supernatant
  4. Supernatant is transferred to a new tube and centrifuged at a higher speed
  5. Next set of organelles settle into a pellet
  6. Repeat steps 4 and 5, increasing speed each time
• Name the 3 heaviest organelles in order


  1. Nuclei
  2. Chloroplast
  3. Mitochondria
• what is the lightest organelle?


  ribosomes