Maginfication And Ultracentrifugation Flashcards
Optical microscopes
Light microscope in which beams of light is focused by glass lenses to produce maginified images
Cheaper easier to maintain
Can view living organisms
Not a very high resolution so see organelles in less detail
Transmission electron microscope
TEM
Beams of electrons transmitted through a thin specimen focusing the electrons on a screen or film
Good resolution gives nice internal images
Must be in a vacuum
Can’t be manipulated with
Scanning electron microscope
SEM
Scan a fine beam of electrons onto specimen and collect electrons scattered
Gives great 3D external images
Good resolution
Bar magnification calculation
Bar length/bar scale(number written)
Bar scale actual size
Image length/bar length x bar scale
Magnification
Image/actual image
Microscopy comparison model answer for resolution
Electron microscopes have a higher resolution than light microscopes
This is because electron microscopes have a shorter wavelength
So you can see the organelles more clearly
1) cell fractionation
The process where cells are broken up so the organelles are separated out
Before fractionation begins the cell is put into a solution which is
Cold-to reduce enzymes breaking down organelles
Isotonic-to prevent bursting/shrinking of cell through osmosis
Buffered-to maintain a constant pH (so enzymes don’t denature etc)
The solution is the same concentration as the cell why?
To prevent cell shrinking or bursting via osmosis
2)homogenation
Cells are broken up in a homogeniser The homegenate(resulting fluid) is filtered to remove any complete cells and large debris
3)ultracentrifugation
Tube of homogenate is spun at low speed so nuclei (heaviest) are forced into pellet at bottom by centrifugal force
Supernatant (fluid at top)is removed leaving the sediment of nuclei
Supernatant is spun again at faster speed forcing chloroplasts to the bottom
Process is repeated for all organelles
Order of pellet formation
Nuclei Chloroplast Mitochondria Golgi apparatus and ER ribosomal structures Left with cytoplasm only
Magnification vs resolution
Magnification is how many times bigger the image is compared to the real object
Resolution is the minimum distance apart that two objects can be in other for them to appear as separate items.
Artefacts
The preparation of material for any kind of electron microscope greatly changes its nature forming structures that were not there originally.
These are called artefacts.
