Analysis Of Cells Flashcards
What is the equation for magnification?
Size of image
________________
Size of real object
How many micrometers are in a mm?
1000
What are the two types of microscope?
Optical (light) and electron
What is the magnification of an optical microscope?
X1500
What is the magnification of an electron microscope?
X1500000
How do TEMs work?
Use electromagnets to focus a beam of electrons on a specimen (darker parts - more dense, more electrons absorbed)
Give an advantage and disadvantage of a TEM
High resolution
Thin specimens only
How do SEMs work?
Scan a beam of electrons across the specimen and knock off electrons, electrons gathered in cathode ray tube to form image
Give an advantage and disadvantage of TEMs
Thick specimens
3D
Lower resolution than SEM
How do you prepare a temporary mount?
Drop of water on slide
Tweezer thin section
Drop of stain e.g. Iodine in potassium iodide
Cover slip using mounted needle
What are the 3 phases of cell fractionation?
Homogenisation
Filtration
Ultracentrifugation
Describe the homogenisation of cells
Cells are vibrated or ground up
Breaks up plasma membrane and releases organelles
Ice cold, isotonic, pH
In homogenisation, why should the solution contain a buffer, be isotonic and ice cold?
Maintain pH
Prevent osmosis damaging organelles
Stop enzymes working/breaking down organelles
Describe the process of filtration
Homogenised cell solution passes through gauze to separate large cell debris
Describe ultracentrifugation
Cell in tube spun in centrifuge at low speed
Heaviest organelles form thick sediment at bottom (pellet)
Other organelles stay suspended (supernatant)
Supernatant drained off
Repeat
What are the heaviest and lightest organelles?
Nucleus and ribosome
What is meant by magnification?
How much bigger the image is than the specimen
What is meant by resolution?
How detailed the image is
How well a microscope can distinguish two points that are close together
What are artefacts?
Something you see down a microscope that isn’t part of the specimen e.g. Air bubble, dust
What is needed to measure size of object under microscope?
Graticule
Stage micrometer
