Cell structure

• How to calculate size of image?

  magnification x actual size
• How to calculate actual size?

  size of image/magnification
• How to calculate magnification?

  Image size/actual size
• List 3 main stages involved in cell fractionation

  Homogenisation, filtration and ultracentrifugation
• What is the heaviest organelle?

  nucleus
• What is the lightest organelles?

  Ribosomes
• why does the solution have to be cold?

  To prevent any unwanted chemical reactions by enzymes
• Why does the solution have to be isotonic?

  To prevent organelles shrinking or swelling due to osmosis
• What is cell homogenation


  The breaking of a cell in order for the different organelles to separate out in a homogeniser
• Why must the homogenate be filtered?

  To remove any large cells or large pieces of cell membrane
• What are the first three steps at the start of centrifugation?

  1 - the homogenate is spun in a centrifuge

  2 - organelles fall to the bottom (order depending on density) forming pellet

  3 - the supernatant is removed and spun at a higher speed
• Explain why an ice-cold, isotonic, buffered solution is used in cell fractionation.

  Ice- cold: slow enzyme activity

  Isotonic: prevent damage to organelles

  Buffered: control pH