Viruses: Structure & Properties
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13 terms
Terms | Definitions |
|---|---|
 What are Koch's postulates? | To prove that an agent causes disease it must: Be found in lesions. Isolate in pure culture. Inoculate pure culture & cause disease. Recover again from lesions of host. |
| What is the method for indirect demonstration of viruses? | Grind infected tissue into fluid suspension. Filter to retain bacteria/fungi and protozoa. Inoculate filtrate into to test animals/plants. Watch for disease. Repeat and pass in series. (Show particulate nature by ultracentrifugation). |
| What are the technical advances for the demonstration of viruses? | Whole animals/plants/bacteria (in vivo). Chick embryos (in vivo) - Used to produce influenza vaccine Discovery of viral genetic material (DNA/RNA). Tissue culture - Used for vaccines and diagnostic reagents. Electron microscopy - Defines morphology by negative staining or thin section. Various molecular techniques. |
| What is tissue culture? | Single cells grow as a monolayer on a flat surface (glass/plastic). Cells are covered by a medium containing nutrients + antibiotics + pH indicator. |
| What is the structure of a virus? | Virion - Infectious virus particle consisting of nucleic acid. Capsid - Composed of capsomeres and has either icosohedral or helical symmetry. Lipoprotein envelope. |
| What are the functions of viral proteins? | Structural - Capsid proteins, viral surface proteins. Non-structural - Enzymes concerned with various aspects of the replication cycle. |
| How was hepatitis C virus discovered? | Ultracentrifugation of plasma from chimps. Extraction of nucleic acid from pellet. Cloning of the bacterial virus (bacteriophage). Grow bacteriophage clones in bacteria. Screen clones for virus protein with human anti-serum. DNA from the only +ve clone sequenced. Use sequenced DNA as probe for virus which turns out to be an RNA virus. |
| Bacteriophage. | A virus that is parasitic in bacteria. It uses the bacterium's machinery and energy to produce more phage until the bacterium is destroyed and phage is released to invade surrounding bacteria. |
| How do you classify viruses? | Viruses are classified in families depending on: Genome (DNA/RNA, ss/ds, +/- sense RNA, polycistronic or segmented). Strategy of replication. Morphology (icosohedral/helical/complex, +/- envelope). Size. |
| What are submicroscopic infectious agents? | Viruses, viroids and prions. |
| What is a viroid? | A single stranded RNA molecule that has no surrounding capsids (protein coat) and only infect plants. |
| What is a prion? | A small proteinaceous infectious particle which is resistant to most procedures that modify nucleic acids. |
| What are the general properties of viruses? | Infect animals, insects, plants, bacteria. Size - submicroscopic (20-300 nm diameter). Classified by morphology and behaviour. DNA or RNA + protein coat ± envelope. Extracellular infectious phase. Obligatory intracellular replication. Viral genes subvert cell biosynthesis to replicate. |
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