Methods of Studying Cells

• Transmission electron microscope

  -Electrons pass through a thin sample (dead specimen) -Denser areas absorb more electrons- appear darker on micrograph -Image is 2D - cross section slice -Magnification around x500,000 -B&W only
• Scanning electron microscope

  -Electrons bounce off surface of specimen (dead - vacuum/stain)

  -3D view

  -Mag around x100,000

  -Black and white only
• Cell fractionation - solution reasoning

  Cold- slow down enzyme activity to prevent damage to or digestion of organelles

  Buffered- kept at a constant pH so there are no fluctuations and no denaturing of enzymes or damage of the organelles

  Isotonic- same water potential as organelles so that they don't shrivel or burst
• Cell Fractionation - Describe + Explain

  -Add cells to solution that is:

  -cold

  -buffered

  -isotonic

  -Homogenize to break open cells and release organelles (crudely )

  -Filter to remove cell debris

  -Ultracentrifugation- Low spin in centrifuge first to remove densest organelles (eg nucleus) as pellets sedimented at bottom

  - rest of organelles still in supernatant

  -so spin again at higher speed to remove less dense organelles in order of most to least dense (inversely prop relationship between centrifuge speed and organelle density)