Heaphy 4 Virology

Question 1

Uses of virology

-Medicine

Answer 1

Features of gene expression by studying simpler organisms

Question 2

Uses of virology

-Biotech

Answer 2

Gene therapy based on virus vector

Question 3

Uses of virology

-Environmental

Answer 3

average bacteria lives less than day, killed by viruses

Question 4

Viroids:

Answer 4

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.

Question 5

Virusoids (‘satellite’):

Answer 5

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

Question 6

Hepatitis B :

Answer 6

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.

Question 7

Virus:

Answer 7

Obligate intracellular parasites. Have to grow inside cells to assemble 2002 – some change morphology outside of cells.

Question 8

Virus - Morphology:

Answer 8

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)

Question 9

virions,

Answer 9

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.

Question 10

PRIONS

Answer 10

”: infectious protein! believed to consist of a single type of protein with no nucleic acid component.
Creutzfeldt-Jakob disease, scrapie & bovine spongiform encephalopathy.

Question 11

variolation:

Answer 11

To be infected with low, and deliberate exposure.

• Recognized that survivors were protected from subsequent infection,

Question 12

Vaccines developed

Answer 12

Edward Jenner, Gloucestershire used cowpox-infected material from hand of a milkmaid Sarah Nemes to vaccinate 8 year old James Phipps.

Question 13

Germ Theory of disease

Answer 13

• Robert Koch & Louis Pasteur jointly proposed the ‘germ theory’ of disease in the 1880s.
• Micro-organisms can invade other organisms and cause disease.

Question 14

VIRUS CONCEPT.

Answer 14

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.

Question 15

1898, Martinus Beijerinick

Answer 15

• 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’)

Question 16

Virus taxonomy

Answer 16

• 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.

Question 17

Quasi species:

Answer 17

prone to accumulate mutations=> 10power 15 sequence variants all with diff phenotypic properties => hard to prevent and cure. Common in RNA virus families.

Question 18

Basis of classification:

x3

Answer 18

• 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

Question 19

Origin of Viruses

• Regressive theory:

Answer 19

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.

Question 20

Origin of Viruses

• Progressive theory:

Answer 20

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.

Question 21

Origin of Viruses

• Co evolution theory:

Answer 21

Viruses coevolved with life.

Question 22

Techniques used to Study Viruses

x5

Answer 22

• 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.

Question 23

Cell Culture methods:

Answer 23

• 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.

Question 24

Quantifying viruses

• The plaque assay

Answer 24

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

Question 25

Quantifying viruses
other approaches:
x6

Answer 25

• Many other approaches. -> staining, counting.
• Serology (antibodies and antigens in blood)
• Structural studies, purification, Electron M, X-ray.
• Biochemical, electrophoresis. => BIOCHEMISTry
• Genetic
• Molecular biology, nucleic acid sequencing.