Methods of studying cells Flashcards
What is the magnification equation ?
Magnification = Image size / actual size
What are the conversions between units ?
nm /1000 = um
um/1000=mm
What do optical microscopes use ?
They use a pair of convex glass lenses , this microscope uses light to view the specimen.
Limitations and benefits of an optical microscope ?
Lower magnification , lower resolution , can view living specimen , can see in colour , more portable , less complex to prepare .
What do electron microscopes use ?
They use beams of electrons and are focused by electromagnets
Limitations and benefits of an electron microscope ?
Higher magnification . higher resolution , cannot view living specimen , cannot see in colour , less portable , more complex to prepare, specimens have to be very thin.
What are the two types of electron microscopes?
Transmission electron microscope (TEM) and scanning electron microscope (SEM) .
How does a TEM work ?
A beam of electron passes through a thin section of the specimen . Areas that absorb the electron appear darker.
How does SEM work ?
A beam of electrons passes across the surface and scatter , pattern of scattering builds up a 3D image .
Which electron microscope has a lower resolving power ?
SEM
What is cell fractionation?
Cell fractionation is the process in which different parts and organelles of a cell a separated so
that they can be studied in detail. The most common method of cell fractionation is differential
centrifugation.
What is the first step of homogenation ?
The cells are first blended in an homogeniser forming the resultant fluid called the
homogenate .Filter solution to remove any debris . This tube of homogenate is then placed in a centrifuge and spun at a slow
speed
What is the second step of homogenation ?
The heaviest organelles, the nuclei, are forced to the bottom of the tube where a thin
sediment forms.
What is the third step of homogenation ?
The fluid at the top, called the supernatant, is removed which leaves just the sediment of
the nuclei. The supernatant is then transferred to another tube and spun at a slightly faster
speed. This time the pellet that forms contains the next heaviest organelle, the
mitochondria.
What is the fourth step of homogenation ?
This process continues so that each time the speed is increased the next heaviest organelle is
sedimented and separated out.
What are the conditions that the homogenate is placed in and why ?
The homogenate at the beginning is placed in a cold, buffered solution of the same water
potential as the cells. This is to prevent the organelles from bursting under osmotic pressure,
to inactivate any enzymes from breaking down organelles and so that the pH does not
fluctuate.
What is the order of separation ?
nuclei - chloroplast (only plants ) - mitochondria - lysosomes - endoplasmic reticulum - Golgi - ribosomes
