Analysis of Cell Components

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  • Created by: katrina
  • Created on: 29-04-13 10:14

Magnification and Resolution

Magnification - how much bigger the image is than the specimen (the sample your looking at)

Formula for magnification = length of image/length of specimen

ie. if you magnified image that's 5mm wide and your specimen is 0.05mm wide the magnification is: 5/0.05= times 100

Resolution - how detailed the image is. More specifically, it's how well a microscope distinguishes between two points that are close together. If a microscope lens can't seperate two objects, then increasing the magnificationwon't help.

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Light and Electron Microscopes

Light Microscopes;

  • They use light.
  • They have lower resolution than electron microscopes.
  • They have a maximum resolution of about 0.2 micrometres (um).
  • The maximum useful magnification of a light microscope is about times 1500.

Electron Microscopes;

  • They use electrons instead of light to form an image.
  • They have a higher resolution than light microscopes so give a more  detailed image.
  • They have a maximum resolution of about 0.0001 micrometres (about 2000 times higher than light microscopes.)
  • The maximum useful magnification of an electron microscope is about 1,500,00.
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Electron microscope; TEMs and SEMs

Transmitting Electron Microscopes (TEMs);

  • TEMs use elctromagnets to focus a beam of electrons, which is then transmitted through the specimen.
  • Denser partsof the specimen absorb more electrons, which make them look darker on the image you end up with.
  • TEMs are good because they give high resolution images.
  • But they can only be used on thin specimens.

Scanning Electron Microscopes (SEMs);

  • SEMs scan a beam of electrons across the specimen.
  • This knocks of electrons from the specimen, which are gathered in a cathode ray tube to form an image.
  • The images you end up with show the surface of the specimen and they can be 3D.
  • But they give lower resolution images than TEMs.
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Cell Fractionation Seperates Organelles

1) Homogenisation -  breaking up the cells. e.g. by vibrating the cells by grinding the cellsup in a blender. Thsi breaks up the plasma membrane and releases the organelle into the solution.

2) Filtration- gettng rid of the big bits. The solution is filtered though a gauze to seperate any large cell debris or tissue debris. The organelles are much smaller than the debris, so they pass through.

3) Ultracentrifugation - Seperating the organelles.

- The cell fragments are poured into a tube. This tube is put into a cetrifuge and spun at a low speed. the heaviest organelles, like nuclei, get flung to the bottom - the pellet. The rest of the organelles stay suspended in the fluid above the sediment - the supernatant.

- The supernatant is drained off, poured into another tube, and spun in a centrifuge at a higher speed.

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