Cells (AQA AS Biology) PART 3 of 6 TOPICS
Methods of studying cells:
- Cheaper than electron microscopes
- Magnification and resolution is not as electron microscopes
Transmission electron microscopes
- Specimen has to be dead
Scanning electron microscopes
- Gives 3D structure of organelles
- It is very expensive
Cell fractionation has three processes:
- Homogenisation is where the cell membrane is broken to release the organelles into an ice cold (preventing enzyme activity), isotonic (preventing shrivelling and bursting of organelles) buffer (to keep the pH constant to prevent the enzymes and organelles from denaturing).
- Filtration is where the cell membrane is separated from the organelles as well as large debris using a gauze.
- Ultracentrifugation is where the organelles are separated from each other. All the organelles are poured into a tube and centrifuged where it is spun at high speed at an angle. Heaviest organelles such as nuclei form a pellet at the bottom with all the lighter organelles at the top called the supernatant. The supernatant is drained off into another tube where it is spun at a higher speed at an angle to get the next heaviest organelles (mitochondria) and the process is repeated until all the organelles are separated.