Section 1: Introduction to Virology

Question 1

Viral history

Answer 1

Greece/Mesopotamia
-the Iliad, Homer describes Hector as rabid
-1000 BC, Mesopotamian law dictates how to be responsible for Rabid dogs
-Egyptian hieroglyphs depict withered legs, typical of poliomyelitis
-evidence of smallpox being endemic in the Ganges River basin- 500 BC (later to decimate the native peoples of the Americas- 1400 BC)
- Agriculture and the domestication of animals changed the ways of humans and viruses interact

Question 2

Variolation

Answer 2

-inoculation, of healthy individuals with material from smallpox pustules into a scratch was widespread in China and India- 1000 AD

Question 3

Vaccination

Answer 3

-vacca = cow
-Edward Jenner (1790s) observed that milkmaids were protected against smallpox
-extracts from cowpox lesions protected individuals against smallpox
-Louis Pasteur coined the term vaccination in the 1800s in honor of Jenner
-Cowpox virus and vaccinia virus are not the same, at some point during the history of passing cowpox from animal to human vaccinia appeared,,, and no one definitely knows how

Question 4

tobacco mosaic disease (TMV)

Answer 4

-first virus was discovered in 1892, by Ivanovsky
-Beijerinck discovered the agent causing the disease was ultra filterable (smaller than bacteria, virus = poison)

Question 5

Bacteriophage

Answer 5

• phage = eating
  -discovered by Twort in 1915 and named for their ability to lyse bacteria on agar plates

Question 6

Properties of Viruses

Answer 6

1. Infectious obligate intracellular parasites
2. Genome is either DNA or RNA
3. Viral genome is replicated and directs synthesis, by cellular systems, of other viral components
4. Progeny virus particles, Virions are formed by de novo assembly from synthesized components in host
5. A progeny virion assembled during the infectious cycle is the vehicle of transmission of the viral genome to the next host

Question 7

Lytic cycle

Answer 7

-infection resulting in lysis

Question 8

lysogenic (lysogeny)

Answer 8

-infection results in the integration of viral DNA into host genome (Prophage)
-longer run time

Question 9

viroids

Answer 9

-infectious agents of plants, a single molecule of RNA

Question 10

prions

Answer 10

-infectious protein molecules

Question 11

Viral classification

Answer 11

-all life must produce mRNA to thus create proteins, this led to the modern classification of viruses

Question 12

The Baltimore classification

Answer 12

-Based on the genetic system of each virus and the relationship between viral genome and mRNA
-Positive strand or Sense (+)
-Negative strand or Sense (-)
-single-stranded (ss) nucleic molecule
-double-stranded (ds) nucleic molecule

Question 13

Positive strand or Sense (+)

Answer 13

immediately translatable information
-makes sense

Question 14

Negative strand or Sense (-)

Answer 14

-the complement to a positive sense DNA or RNA molecule

Question 15

Viral genetic content

Answer 15

DNA viruses contain ssDNA and dsDNA
-mostly are dsDNA
-mostly are not simple linear molecules

RNA viruses are mostly ssRNA molecules
-can be -, +, or ambisense
-most viruses appear rod-shaped or spherical under electron microscopy, this is due to the economy of viral construction of the plasmid

Question 16

Where is viral genetic material contained

Answer 16

1. capsid (contains the material within itself)
2. nucleocapsid

Question 17

Capsid symmetry

Answer 17

-capsids are constructed from a small number of protein subunits by using helical symmetry (rod-shaped) or the symmetry of platonic polyhedra (tetrahedron, icosahedron, etc, spherical

Question 18

helical symmetry

Answer 18

-imagine a two-dimensional lattice and rolling it into a cylindrical structure

Question 19

icosahedral symmetry

Answer 19

-most efficient way of forming a spherical shell to maximize internal volume (the simplest case is an icosahedral symmetry with 20 triangular faces)

Question 20

complex particles

Answer 20

-form complex capsids with structures that are poorly understood (ex: retroviridae)

Question 21

Enveloped viruses

Answer 21

-enveloped viruses have a lipid membrane acquired from the host that surrounds the capsid, naked do not have an envelope
-easy to get rid of

Question 22

Class I

Answer 22

dsDNA
-viruses contain dsDNA as their genome, their mRNA directly transcribed from the DNA template
ex: herpes simplex (herpesvirus)

Question 23

Class II

Answer 23

ssDNA
dsDNA
-viruses have ssDNA as their genome, they convert DNA to double stranded form before RNA is transcribed
ex: parvovirus

Question 24

Class III

Answer 24

dsRNA
- their mRNA is transcribed from the RNA genome
ex: rotavirus (childhood gastroenteritis)

Question 25

Class IV

Answer 25

(+)ssRNA
(-)ssRNA
- the positive polarity means their genomic RNA can serve directly as mRNA
-negative polarity (complement of positive strand genomic RNA) are formed from intermediates and serve as a template for the production of RNA with positive polarity
ex: picornavirus

Question 26

Class VI

Answer 26

(-)ssRNA-RT
DNA/RNA
dsDNA
-viruses have diploid ssRNA genomes that need to be convert with reverse transcriptase to dsDNA, this is then put in the nucleus of host cell, then mRNA can be produced by transcription of viral DNA
ex: Human immunodeficiency virus (HIV)

Question 27

Class V

Answer 27

(-)ssRNA
-viruses contain a ssRNA genome with negative polarity, so their sequence is complementary to mRNA. So the negative stranded genome can be converted directly to mRNA.
ex: rabies (rhabdovirus)

Question 28

Class VII

Answer 28

dsDNA-RT
-viruses have partial dsDNA genomes and make ssRNA intermediates that act as mRNA, but are also converted back into dsDNA genomes by reverse transcriptase, necessary for genome replication.
- ex: Hepatitis B virus (hepadnavirus)

Question 29

Naked particles

Answer 29

-naked particles are harder to get rid of (intestinal viruses), they just contain the viral capsid so they can survive a very long time (have to bleach it to dissolve it)