Continued from Manhua's Methods of study of Viruses i am going to talk about the physical methods used to view virus.


They are mainly:

• X-ray crystallography
• Electron microscopy - Transmission Electron microscopy, Scanning Electron microscopy and the STEM (Scanning Transmission Electron Microscope)
• Ultracentrifugation where purification is used.


Basically, they are used to study the virus and the virus genome.
X-ray crystallography is a method used to determine atoms in the crystals with an illustration of the picture is on the right. The rays are being scattered on to the crystal, forming a lot of rays which gives an density make up of the virus.


The Electron microscopy is a microscope used to enlarge objects up to 2 million times, using electrons to give an idea of the object. As compared to a light microscope which can only magnify up to 2000 times, the electron microscope have a higher resolution due to the wavelength of the electron. With a electrostatic and electromagnetic lenses, the image is then formed by controlling the electron beam to focus on the object to form the magnified image.

The difference between the 3 Electron microscope is that the Transmission Electron microscope uses a high voltage electron beam to create an image.

While the
Scanning Electron microscope,( picture of it is at the right) produces the image with a electron beam that is focus and scan over the specimen.
Unlike the Transmission Electron microscope, it does not carry a complete image of the specimen.

Lastly, the Scanning Transmission Electron Microscope
STEM use beam like
use of SEM’s beam which transmits and simplifies dark-field images. Thus, the specimen is taken in serial but not in parallel fashion.



Then, is the Ultracentrifugation where purification is used. In ultracentrifugation, either sucrose gradients or organelles. gradients of caesium salts are used to study the virus.
Using the sucrose gradient, the cellular organelles are being separated followed by the gradient of caesium salts are used to separate the nucleic acids. Then, the sample are being spun at high speed for sufficient time to produce the separation for the gradient to be isolated and then separated.