Lecture 4 Flashcards
How big is a typical virus?
20-400 nm
What is a virus?
Obligate intracellular parasites
What are viruses made of?
Proteins
Nucleic acid
Sometimes lipids
What are viroids?
Naked circular RNAs associated with plant diseases
How big are viroids generally?
200-400nt
What are virsoids?
Circular RNAs which are larger than 1000nt long dependent on the presence of a helper virus replication for multiplication
What are prions?
Infectious aggregated proteins
How did people prevent the spread of smallpox on China in 1000BC?
They recognised that survivors were protected from subsequent infection. They inhaled dried crusts or inoculation of pus from lesion into a scratch on the forearm.
When did Edward Jenner invent the modern vaccine?
1796
How did edward jenner protect against smallpox?
Edward Jenner used cowpox-infected material from hand of a milkmaid to vaccinate an 8 year old James Phipps. He was not infected when later inocculated with smallpox
Who proposed the germ theory of disease?
Robert Koch and Louis pasteur
Who demonstrated that something smaller than bacteria must be causing disease? How and when did he do this?
Dimitri Iwanowski
He used extracts of diseases tobacco plants and passed them through ceramic filters which retain the smallest known bacteria
1892
Who developed the modern idea of a virus? When did he do this? What did he call it?
Martinus Beijerinick
1898
Vivum fluidum
How are viruses classified?
Using a hierarchical classification system
What suffix to familes of viruses have?
viridae
What suffix do virus genus’ have?
virus
What are the three main bases of classification of viruses?
Morphology
Physiochemical properties
Genome
What are the three theories on the origin of viruses?
Regressive theory
Progressive theory
Co- evolution theory
Describe the regressive theory on the origin of viruses
They are degenerate forms of intracellular parasites which lost genomic complexity.
What is the problem with the regressive theory for the origin of viruses?
It doesn’t account for RNA viruses
Describe the progressive theory of viruses
Normal cellular nucleic acids gained the ability to replicate autonomously and to evolve. So DNA viruses would originate from plasmids or transposable elements and RNA viruses would originate from mRNA
Describe the co-evolution theory of the origin of virused
Viruses co-evolved with life
Who developed the mouse model of yellow fever?
Walter Reed
What are the seven different ways of quantifying viruses?
The plaque assay Serology Structural studies Biochemical Genetic Molecular biology Chemistry
What is a plaque assay?
Once a virus infected culture is stained we can count the number of plaques which are holes in the lawn of bacteria
What is serology?
Antibodies and antigens in the blood are identified
