Methods of Studying Cells

12 Questions

What is the main difference between a light microscope and an electron microscope?

Light microscopes use visible light while electron microscopes use a beam of electrons

What is the formula used to calculate the magnification of an image in a microscope?

Magnification = size of image / size of real object

What is the main purpose of the vacuum environment in an electron microscope?

To prevent the electrons from being deflected out of the beam alignment

What is the primary difference between a transmission electron microscope (TEM) and a scanning electron microscope (SEM)?

TEMs use a beam of electrons that passes through the specimen, while SEMs use a beam of electrons that scans the surface of the specimen

What is the relationship between the resolution of a microscope and the wavelength of the light or electrons used?

The resolution is inversely proportional to the wavelength of the light or electrons

What is the main limitation of light microscopes compared to electron microscopes?

Light microscopes have a lower resolution than electron microscopes

What is the main purpose of cell fractionation?

To separate different organelles within a cell for further study

Which of the following is a key limitation of using electron microscopes?

All of the above

What is the purpose of the homogenization step in cell fractionation?

To break up the cells into a fluid mixture containing all the organelles

What is the main difference between a Transmission Electron Microscope (TEM) and a Scanning Electron Microscope (SEM)?

TEM uses a beam of electrons that passes through the specimen, while SEM scans the surface of the specimen

What is the purpose of the buffered solution used in the cell fractionation process?

All of the above

Which of the following is a key advantage of using a Transmission Electron Microscope (TEM) over a light microscope?

TEM has a higher resolving power than light microscopes

Study Notes

Electron Microscopes

Transmission Electron Microscope (TEM):
- A beam of electrons passes through a thin section of a specimen
- Areas that absorb electrons appear darker on the electron micrograph
Scanning Electron Microscope (SEM):
- A beam of electrons passes across the surface and scatters
- The pattern of scattering builds up a 3D image depending on the contours of the specimen
Limitations of Electron Microscopes:
- The whole system must be in a vacuum, making it impossible to observe living specimens
- A complex staining process is required, which may introduce artefacts into the image
- Specimens have to be very thin, particularly for TEM
- SEM has a lower resolving power than TEM, but both have greater resolving power than a light microscope

Cell Fractionation and Ultracentrifugation

Cell fractionation is the process of separating different parts and organelles of a cell to study them in detail
The most common method of cell fractionation is differential centrifugation
Steps of differential centrifugation:
- Homogenization: blending cells in an homogeniser to form a homogenate
- Centrifugation: spinning the homogenate at a slow speed to sediment the heaviest organelle (nuclei)
- Removing the supernatant and transferring it to another tube
- Spinning at a slightly faster speed to sediment the next heaviest organelle (mitochondria)
- Repeating the process to separate out other organelles

Cell Structure

All living organisms are made up of cells, with various types of cells sharing common features
Eukaryotic cells, found in humans, contain a nucleus and membrane-bound organelles

Microscopes

Light Microscopes:
- Use convex glass lenses to resolve images 0.2um apart
- Limited by the wavelength of light, restricting resolution
Electron Microscopes:
- Can distinguish between items 0.1nm apart
- Allow for higher resolution than light microscopes