3053654
Description
Flashcards by mitzigolsorkhi, updated more than 1 year ago
|
Created by mitzigolsorkhi
almost 9 years ago
|
|
| Question | Answer |
| How is electron microscopy better than a light microscope? | - capable of higher magnification - greater resolving power = you can see smaller objects in greater detail |
| How do you achieve greater resolution? | - the faster you ACCELERATE the electron beam, the SHORTER their wavelength |
| How is acceleration measured? | in kV |
| 100,000 V gives... | - a wavelength (resolution) of 0.004nm - producing a magnification of x500,000 |
| what are two types of electron microscopy (em)? | - TEM (transmission) - SEM (scanning) |
| 4 steps of TEM are... | 1. Tungsten cathode emits electron beam 2. Specimen = v thin to allow electron penetration 3. Image is magnified via magnetic lenses and recorded via a fluorescent screen 4. Gives info on structure - 2D black and white image w 0.2nm resolution (Tarty Sam Is Great) |
| 4 steps of SEM are... | - Lower beam acceleration - Detects secondary electrons emitted from the surface of the specimen -Detectors build up image by mapping detected signals w beam positioning - Greater depth of view, gives 3D black and white image w 2nm resolution (Ladies Do Dance Great) |
| pros and cons of TEM | - See inside the cell - Bad resoution |
| pros and cons of SEM | - Only see the outside of the cell - Good resolution |
| Name the 6 types of preparation of the specimen for EM | 1. Cryofixation 2. Fixation 3. Dehydration 4. Embedding 5. Sectioning 6. Staining CFDESS (So Called FEDS) |
| Cryofixation is... | RAPID FREEZING in liquid nitrogen - minimal artefacts but time sensitive |
| Fixation is | glutaraldhyde often used to crosslink protein molecules and osmium tetroxide to PRESERVE LIPIDS - can leave artefacts - store for ages |
| Dehydration... | replaces water with organic solvent (ethanol or acetone) |
| Embedding... | - after dehydration, infiltrate tissue with wax of resin - lasts ages - leaves artefacts |
| Sectioning | - produce thin slices necessary for EM (90nm) cut via ultra-microtome knife |
| Staining | - uses heavy metals to increase electron density - therefore increases electron scatter giving greater contrast |
| Disadvantages of EM are... | VERY EXPENSIVE - Needs constant high voltages needs continuous vacuum system - housed in special building to keep vibration and external magnetic field muted - preparations of samples = timely and expensive |
Want to create your own Flashcards for free with GoConqr? Learn more.