Methods of studying cells

• The human eye can only view objects up to 0.1mm in size. This means it has a limited magnification and resolution.
• Magnification: How many times bigger an image appears than the actual object.
• Resolution: Minimum distance at which two distinct points can be distinguished.
• Optical microscopes use light to manipulate samples, it is then magnified by a lense.
• Positives of an optical microscope:

  • Cheap and easy to use
  • Provides a coloured image
  • You can examine a whole cell
  • Living samples can be used
• Negatives of an electron microscopes:

  • A limited magnification (1000x)
  • A limited resolution (200nm)
  • Can only view eukaryotes and nuclei
• There is two types of electron microscopes. Both use electrons to manipulate an image.
• Positive of electron microscope:

  • A shorter wave length than a light microscope which provides a better magnification and resolution
• Disadvantage of electron microscopes:

  • Specimens must be dead as it is in a vacuum.
• A TEM transmits electron beams through the sample to provide an image
• Positives of a TEM:

  • A high resolution
  • A high magnification
  • Allows intercellular detail
• Negatives of a TEM:

  • Specimens must be thin
  • Expensive and slow to use
  • Has to be kept in a vacuum
  • No living samples can be used
• A SEM emits beams across a specimen. These bounce off surfaces and any electrons used.
• Positives of a SEM:

  • Thicker samples can be used
  • Gives a 3D external suface
  • Captures textures
• Negatives of a SEM:

  • Can't view the inside of a cell
  • Lower resolution then a TEM
  • No living specimens
  • Slow to use
• Cells need to be kept at 3 specific conditions before they are examined:

  • Cold to prevent enzyme activity
  • pH buffered to prevent enzyme activity and protein denaturing
  • Same water potential to tissue to prohibit osmosis, prevent dissolving and bursting under osmosis
• Homogenation:

  Place cells in a homogenphier (blender)

  Produces a fluid called homogonate

  Filter to remove any large peices and remove any incomplete cells
• Ultracentrefigation:

  Spins the homogonate to force cell organelles to leave

  Start at a low speed which removes the nucleus

  This then settles at the bottom of the test tube and when removed a supernatant is left

  Increase the speed if nucleus isn't wanted and repeat until organelle needed is released.