Flashcards in 02/27f Virus Ultrastructure Deck (15)
What signals are detected by a transmission electron microscope?
Electrons that are not bounced back or scattered by the sample (transmitted electrons)
What signals are detected by a scanning electron microscope?
Secondary electrons (bounced out from the sample)
What happens when outer shell electrons fall down energy levels to fill vacant orbits?
X-rays are released
What two specimen preparation methods are used for EM samples? For what types of specimens is each method used?
Negative staining - for fluid specimens
Ultrathin sectioning - for cells and solid tissues
How is negative staining performed?
Fluid sample is spun down
Supernatant is placed on a waxy substance, which causes it to bead up
A tiny grid coated with a support film is placed over the sample bead
The grid is then wicked, placed on a droplet of stain, wicked again, and placed in the microscope
What does the negative stain actually stain?
Background (what you're NOT interested in)
How is ultrathin sectioning performed?
Tissue is fixed and embedded in an epoxy resin
Ultrathin (60-90nm) sections are cut on a microtome
Section is then placed onto an EM grid
What are the two basic morphologies of viruses?
What are the morphological characteristics of naked viruses in negative staining?
Hard and hardy
What are the morphological characteristics of enveloped viruses in negative staining?
Encased in pleiomorphic membrane - may appear smooth or "spiky"
Nucleocapsid contained within the membrane
What are the possible shapes of the nucleocapsid?
Where are DNA viruses usually seen in ultrathin sections? What about RNA viruses?
DNA viruses - nucleus
RNA viruses - cytoplasm
Where is poxvirus (a DNA virus) formed?
In the CYTOPLASM (atypical)
For what types of clinical procedures are EM particularly useful?
Differentiating viral infections
Identifying emerging viruses
Identifying weird, mysterious infections