CELLS: Analysing Cell Components Flashcards
Magnification
How much bigger the image is than the specimen
Resolution
How easily a microscope distinguishes between two points that are close together.
What are the two main types of microscope?
Optical
Electron
Optical microscope:
- How does it form an image?
- Maximum resolution?
- Maximum useful magnification?
- Forms an image using light
- Maximum resolution of 0.2 micrometres
- Max useful magnification = x 1500
Electron microscope:
- How does it form an image?
- Maximum resolution?
- Max useful magnification?
- Uses electrons
- Higher resolution of about 0.0002 micrometres
- Max useful magnification x 1500000
What are the 2 types of electron microscopes?
Transmission (TEMs)
Scanning (SEMs)
How do TEMs work?
- Electromagnets focus beam of electrons that is transmitted through specimen.
- Denser parts absorb more = darker image
What is a strength and limitation of TEMs?
+ High resolution images, so can see internal structures of organalles
- Thin specimens needed
How do SEMs work?
- Scan beam of electrons across specimen.
- Knocks off electrons from specimen, which gather in cathode ray tube to form image
- Shows surface, 3D images
What is a strength and limitation of SEMs?
+ Thick specimens
- Lower resolution images
How do you convert from micrometres to mm?
Divide by 1000
How do you prepare a temporary mount of a specimen on a slide?
- Pipette small drop of water onto slide
- Use tweezers to place thin specimen on top of water
- Add a stain
- Add cover slip to protect.
How are organelles separated?
Using cell fractionation
What are the 3 steps of cell fractionation?
- Homogenisation - break up cells
- Filtration - removes large pieces
- Ultracentrifugation - separates organelles
What does homogenisation do?
Breaks up plasma membrane
Releases organelles into solution
How might you homogenise cells?
Grinding cells in a blender
In cell homogenisation, what must the solution be?
- Ice-cold - reduces enzyme activity
- Isotonic - prevents damage through osmosis
- Buffered - maintains pH
Describe the process of filtration:
- Homogenised cell solution filtered through gauze
- Separates large cell debris or tissue debris from organelles.
Describe the process of ultracentrifugation:
- Cell fragments poured into tubes
- Tube put in centrifuge + spun at low speed
- Heaviest organelles gather at bottom + form thick sediment (the pellet)
- Supernatent drained off into another tube + spun at higher speed
- Process repeats
Pellet
Thick sediment at bototm of centrifuge formed from heaviest organelles
Supernatent
Fluid above pellet in which the lighter organelles are suspended.
What organelle is likely to be the first separated out in ultracentrifugation?
Nuclei
What organelle is likely to be the second separated out in ultracentrifugation?
Mitochondria
