Heaphy 4 Virology Flashcards
Uses of virology
-Medicine
Features of gene expression by studying simpler organisms
Uses of virology
-Biotech
Gene therapy based on virus vector
Uses of virology
-Environmental
average bacteria lives less than day, killed by viruses
Viroids:
small 200-400nt, naked circular RNAs. No capsid or lipid envelope. Associated with plant diseases. Capable of replicating in cells. Not known to infect animals yet.
Virusoids (‘satellite’):
circular RNAs, larger than viroids ~1000nt.
- Defective viruses/parasite rely on ‘helper’ virus for replication for multiplication, packages genome, into virus capsids as passengers. Present in animals and plants. Associated with disease. Encode proteins
Hepatitis B :
infection of viruses also infect animals and plants associated with liver cancer, via blood. Delta antigen makes it worse is virus that uses Hep B to propagate genome.
Virus:
Obligate intracellular parasites. Have to grow inside cells to assemble 2002 – some change morphology outside of cells.
Virus - Morphology:
Rod shaped or spherical. Typically 20-400nM, sub-microscopic (but a few visible by light microscopy uM in size e.g. pox and pandora virus groups(giant viruse, big genomes)
virions,
do not ‘grow’ or divide, but assemblesed by preformed materials by cell
lack genetic information and apparatus for the generation of metabolic energy or for protein synthesis.
PRIONS
”: infectious protein! believed to consist of a single type of protein with no nucleic acid component.
Creutzfeldt-Jakob disease, scrapie & bovine spongiform encephalopathy.
variolation:
To be infected with low, and deliberate exposure.
• Recognized that survivors were protected from subsequent infection,
Vaccines developed
Edward Jenner, Gloucestershire used cowpox-infected material from hand of a milkmaid Sarah Nemes to vaccinate 8 year old James Phipps.
Germ Theory of disease
- Robert Koch & Louis Pasteur jointly proposed the ‘germ theory’ of disease in the 1880s.
- Micro-organisms can invade other organisms and cause disease.
VIRUS CONCEPT.
1892, Dmitri Iwanowski, Russian, The beginning of virology. showed that extracts from diseased tobacco plants transmit disease to other plants after passage through ceramic filters which retain the smallest known bacteria.
1898, Martinus Beijerinick
- Tobacco mosaic virus isolated and identified.
extended results on tobacco mosaic virus & developed the modern idea of the virus, referred to as contagium vivum fluidum (‘soluble living germ’)
Virus taxonomy
• Hierarchical. Families have suffix viridae. Genus have suffix virus. Species is important definition. BIV (bovine) is not the same hazard as HIV! In many animals.
Order: virales
Families: viridae
Genus: virus
Strain & type= most important classification.
Quasi species:
prone to accumulate mutations=> 10power 15 sequence variants all with diff phenotypic properties => hard to prevent and cure. Common in RNA virus families.
Basis of classification:
x3
• morphology (size, shape, enveloped/ un enveloped) (good but many similar)
physicochemical properties (molecular mass, thermal, ionic stability). (not good)
• genome (RNA, DNA , segmented sequence, etc) more than one strand• Mixture of Morphology & genome is basis for phylogenetic
Origin of Viruses
• Regressive theory:
degenerate forms of intracellular parasites/bacteria. Cf Leprosy bacillus, rickettsiae and chlamydia have all evolved in this direction. RNA virus evolution ? can only replicate in human cells. – does not account for RNA genomes.
Origin of Viruses
• Progressive theory:
Normal cellular nucleic acids gained the ability to replicate autonomously & to evolve.
- DNA viruses from plasmids or transposable elements.
- Retroviruses derived from retrotransposons & RNA virus from mRNA.
Origin of Viruses
• Co evolution theory:
Viruses coevolved with life.
Techniques used to Study Viruses
x5
- Living hosts: Man.
- Pasteur: rabbits to study & develop rabies vaccines.
- Walter Reed: mouse model of yellow fever, virus transmitted disease by flies reduced death rate by changing working hours. Transgenic mice now invaluable
- Embryonated eggs: propagate viruses in the early decades of this century.
Cell Culture methods:
• Whole organ cultures, => cells; primary cell cultures a short period in culture/ immortalized cell lines => HeLa cells grow in culture indefinitely. Viruses grown in them.
Quantifying viruses
• The plaque assay
dilutions of virus infect a cell monolayer, covered with agar to restrict virus diffusion. Results in localized cell killing & the appearance of plaques. The number of plaques directly relates to numbers of infectious virus particles applied to the plate.
• Pfu/cfu
