studying cells Flashcards
-> microscopes, cell fractionation + ultracentrifugation (23 cards)
what is magnification equation?
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A M
how do light microscopes work?
they pass a beam of light through a thin sample
- use glass lenses to focus images
what is magnification?
how enlarged an image is
what is resolution?
the minimum distance apart that two objects can be distinguished as separate objects
advantages of optical microscopes
- cheap
- produce colour images
- easy to use
- can view live specimens
disadvantages of optical microscopes
- low resolution
- low magnification
- specimens must be thin
- stains required
Why do electron microscopes have a higher resolution than a light microscope?
as electrons have a shorter wavelength than the wavelength of light
total magnification equation
objective magnification x eyepiece magnification
how do electron microscopes work?
use a beam of electrons in which pass through/over the surface of a sample
why are EM greyscale?
- some areas absorb electrons more than others
- heavy metal stains are used
why must EM specimens be dead?
as they are viewed in a vacuum
how are TEM images made?
by passing a beam of shorter wavelength electrons through a sample, creating 2D images
how are SEM images made?
by passing a beam of shorter wavelength electrons across the surface of a sample, creates 3D images
advantages of EM
- high resolution so can view smaller organelles
- high magnification
disadvantages of EM
- more complex + expensive
- greyscale images
- artefacts common
- specimens must be dead
what is cell fractionation?
process in which different parts and organelles of a cell are separated so that they can be studied
what are the cells prepared in?
placed in a ice cold, isotonic, buffer solution
why ice cold?
to reduce enzyme activity to prevent organelle damage
why isotonic?
to make the concentration of chemicals the same as the cell to prevent damage by osmosis and shrinkage/ lysis of cells
why buffer?
to maintain constant pH to avoid enzymes/proteins being denatured
homogenisation
- BREAKING = cells broken up by either grinding or vibrating them. Cells blended in ice cold, isotonic, buffer solution
- FILTRATION = homogenised mixture of buffer and cell debris/ organelles is filtered, only organelles pass into filtrate, cell debris filtered out
ultracentrifugation
solution placed into a tube and is centrifuged to separate organelles based on density. A pellet of organelles is left at the bottom of the tube and the supernatant is removed. Each time this is repeated at increasing speeds until the pellet of organelles you want is left
order of organelle density
Nuclei
Chloroplasts
Mitochondria
Endoplasmic reticulum
Ribosomes
