Block 1

Question 1

Define virology

Answer 1

Virology: The study of viruses and viral diseases

Question 2

Define virus

Answer 2

Virus: broad term to describe any aspect of the infectious agent and includes:
i. The infectious (viron) or inactivated virus particle
ii. Viral nucleic acid
iii. Protein in the infected cell

Question 3

Define Virion

Answer 3

Virion: A complete/mature virus particle that consists of an RNA or DNA core
sometimes with external envelopes and that is the extracellular infective form of a virus

Question 4

Define Viroid

Answer 4

Viroid: An infectious particle smaller than any of the know viruses, an agent of certain plant diseases
i. This particle only consists of extremely small circular RNA molecules,
lacking the protein coat/capsid of a virus

Question 5

What is the importance of veterinary virology (3 examples)

Answer 5

a. Viruses cause high rates of mortality and morbidity in animals and birds
b. Viral diseases in animals and birds cause financial loss to livestock and poultry
industries
c. Some viruses are zoonotic

Question 6

viruses are Non living entities
That Contain nucleic acid genome (DNA or RNA) surrounded by a protein coat (and
sometimes an envelope). All viruses are obligate intracellular parasites. What does this mean for the virus when outside and inside the cell?

Answer 6

i. Outside the cell, viruses are inert or dormant particles
ii. Inside the cell, viruses hijack and utilize the host cell’s machinery to
produce its proteins and nucleic acids for the next generation of virus

Question 7

Viruses do not have what, make what, or can reproduce how?

Answer 7

i. Have standard cellular organelles
ii. Make energy or proteins by themselves
iii. Have the genetic ability to multiply by division
1. Viruses reproduce like an assembly line where various parts of the
virus come together from different parts of the host cell to form
new virus particles

Question 8

What is the smallest virus?

Answer 8

Porcine circovirus type 1

Question 9

What is the largest virus?

Answer 9

Poxvirus (200nm diameter & 300 nm in length) → humans,
animals and birds

Question 10

What is pleomorphism?

Answer 10

the ability of some viruses to alter their shape and size

Question 11

What is Electron microscopy?

Answer 11

Biological materials have little inherent contrast → need to be stained
Requires negative staining with electron dense material (Uranyl acetate, Phosphotungstate)

Question 12

What is Cryo-Electron Microscopy (Cryo-EM)?

Answer 12

Allows observation of specimens in their natural environment (not stained or fixed) at cryogenic temperatures

Question 13

What is X-Ray Crystallographic Method?

Answer 13

Virus particles are crystallized and then are reflected with heat from x-rays

Question 14

What is Nuclear Magnetic Resonance (NMR)?

Answer 14

Very high quality images

Question 15

Explain the capsid of a virus

Answer 15

a. Capsid = protein shell of a virus that encases/envelopes the viral nucleic acid or
genome
b. Made up of capsomeres
i. Capsomere = basic subunit protein in the capsid of a virus
c. Most viruses have 1 capsid (except reoviruses which have double layered capsids)
d. Nucleocapsid = Capsid + Virus Nucleic Acid (DNA or RNA)/Genome

Question 16

What is the function of a capsid? (8)

Answer 16

i. Protects viral nucleic acids from enzymes, chemicals, environment
ii. Structural symmetry of the virus
iii. Attachment of the virus specific receptors on the susceptible host cell
iv. Interaction with host cell membranes to form the envelope
v. Uncoating of the genome in the host cell
vi. Transport of the viral genome to the appropriate site
vii. Facilitates specific recognition and packaging of the nucleic acid genome
viii. Contain antigenic sites → determine antigenicity of the virus

Question 17

What is helical symmetry? Animal and plant viruses

Answer 17

i. Animal viruses→ Helical nucleocapsid is enclosed within a lipoprotein envelope
ii. Plant viruses → Naked helical nucleocapsids → no envelope (ex: tobacco mosaic virus)

Question 18

Cubic/Icosahedral Symmetry
Have 2 types of capsomers: pentagonal and hexagonal. Explain

Answer 18

1. Pentagonal → make up vertices (corners/pentons)
   a. There are always 12 pentons
2. Hexagonal → make up facets (hexons)
   a. # of hexons varies with the virus groups

Question 19

What is the T-Number?

Answer 19

Triangulation Number (T-Number)
1. Describes the relation between the number of pentagons and hexagons of the icosahedron
a. T = h^2 + h*k + k^2
b. H and k are the distances between the successive pentagons on the virus surface for each axis
2. Examples:
a. Parvovirus: T=1
i. Simplest icosahedron
ii. Capsid consists of 60 copies of CP protein
b. Reoviridae

i. Outer capsid: T=13 icosahedral symmetry
ii. Inner capsid: T=2 icosahedral symmetry
3. Naked icosahedral vs. enveloped icosahedral

Question 20

What is complex symmetry?

Answer 20

i. Virions are composed of several parts each with separate shapes and symmetries
ii. Ex: pox viruses, bacterial viruses

Question 21

What is the envelope of a virus?

Answer 21

a. A lipid bilayer with embedded proteins
i. Formed from the cellular membrane of a host cell
ii. Maintained only in aqueous or moist environments
b. Inactivated by the the dissolution of lipid membrane with lipid solvents such as:
i. Ether
ii. Chloroform
iii. Sodium deoxycholate, detergents, etc.
c. Enveloped viruses are easier to sterilize than non-enveloped viruses & cannot survive for long periods in the environment

Question 22

What are 3 functions of the envelope of a virus?

Answer 22

i. Facilitate virus entry into host cells
ii. Help the virus adapt fast and evade the host immune system
iii. Can cause persistent infections

Question 23

How is the envelope formed?

Answer 23

Formed by budding of viral nucleocapsid through a cellular membrane
(like cytoplasmic, golgi, or nucleus membranes)

Question 24

There are two types of proteins that make the envelope of a virus. What are they?

Answer 24

i. Glycoprotein (Two types:
External glycoprotein and Channel proteins
ii. Matrix proteins

Question 25

What is the location and and function of the matrix proteins?

Answer 25

1. Location: Between virus capsid and envelope 2. Functions: a. Recognition site of nucleocapsid at the plasma membrane and mediates encapsidation of the RNA-nucleoprotein cores into the membrane envelope b. Link the internal nucleocapsid to the lipid membrane envelope c. Virus assembly d. Allow stabilization of the lipid envelope

Question 26

What are 4 functions of External glycoproteins?

Answer 26

a. External glycoprotein i. Usually major antigens of the virus ii. Functions: 1. Hemagglutination 2. Receptor binding 3. Antigenicity 4. Membrane fusion

Question 27

What are 2 functions of channel proteins?

Answer 27

Channel proteins i. Hydrophobic proteins that form a protein lined channel through the envelope ii. Function: 1. Alter permeability of the membrane 2. Modify the internal environment of the virus

Question 28

What is antigenic drift?

Answer 28

i. Can cause changes in antigenicity or become resistant to drugs ii. Point mutations (silent, nonsense, missense)

Question 29

What is recombination vs reassortment shift?

Answer 29

Recombination 1. Involves the exchange of the nucleotide sequences between different, but close related, viruses during replication 2. Occurs with only one single gene segment Reassortment 1. Most important mechanism for high genetic diversity in viruses with a segmented genome 2. Only occurs with multiple segments of the genome

Question 30

What are enzyme viral proteins required for? (2)

Answer 30

1. mRNA transcription 2. Nucleic acid replication

Question 31

What is Retroviral integrase (IN)? Example?

Answer 31

Produced by retrovirus that enables its genetic material to be integrated into the DNA of the infected host cell Ex) HIV

Question 32

What is Reverse transcriptase (RT)?

Answer 32

Used to generate complementary DNA from a RNA template

Question 33

What is Nucleic acid polymerases?

Answer 33

Viral genome replication

Question 34

What 2 roles do viral nonstructural proteins?

Answer 34

i. Play roles within infected host cell during virus replication ii. Act in regulation of virus replication or virus assembly

Question 35

What is Incomplete virions?

Answer 35

Virions without nucleic acid (empty capsid)

Question 36

What is defective virions?

Answer 36

i. A virus that cannot replicate because it lacks a full complement/copy of viral genes ii. Defective viral particles result from mutations or errors in the production or assembly of virions

Question 37

What is Pseudovirion?

Answer 37

i. Contains non-viral genome with the viral capsid (such as host nucleic acid instead of viral nucleic acid)

Question 38

What is Pseudotypes?

Answer 38

When related viruses infect the same cell, the genome of one virus may be enclosed in the heterologous capsid of the second virus

Question 39

What is Variolation/Inoculation? How did Edward Jenner invent the first vaccine? What was Louis pasteur’s contribution to help cure Rabies?

Answer 39

i. First method used to immunize an against smallpox ii. Material taken from a patient in hopes a mild infection would result Edward jenner → invented vaccination Inoculated cowpox matter repeatedly into arms of a healthy boy who became immune and did not succumb to smallpox Louis Pasteur Injected dried potassium hydroxide treated infected rabbit brain materials to 2 boys bitten by rabid dogs and both recovered

Question 40

What is a chamberland filter and who were some key names who used the filter? (4)

Answer 40

i. Filter with pores smaller than bacteria ii. Dmitri Ivanovski → famous tobacco mosaic virus experiment iii. Fredirich Loeffler & Paul Frosch → passed 1st animal virus through a filter and discovered foot-and-mouth disease iv. Martinus Beijerinck → discovered “viruses” using the chamberland filter

Question 41

What did Walter reed discover?

Answer 41

Discovered yellow fever is transmitted through mosquitoes

Question 42

What did Peyton Rous discover?

Answer 42

Discovered oncogenic viruses (Rous sarcoma virus) Isolated the first tumor-causing animal virus

Question 43

What did Russia and Knoll invent?

Answer 43

Invented electron microscope to see viruses for the first time

Question 44

What did Woodruff, Goodpasture, and Burnet do?

Answer 44

Propagated viruses in eggs Fowlpox virus → first virus successfully propagated in eggs

Question 45

Sanford, Enders and Dulbecco & Vogt contributed to tissue culture how respectfully?

Answer 45

Tissue Culture i. Sanford → culture of isolated mammalian cells ii. Enders → growth of Poliovirus in cell culture iii. Dulbecco & Vogt → plaque assay for first animal virus (poliovirus)

Question 46

Discuss eradication of an infectious disease. What is rinderpest?

Answer 46

a. Eradication involves complete elimination of the pathogen or the disease-causing agent from a defined geographic region b. Rinderpest = only animal disease declared globally eradicated

Question 47

What is Baltimore Classification system?

Answer 47

i. No longer used ii. Based on viral genome

Question 48

What is International Committee of Taxonomy of Viruses (ICTV) Classification System? Purpose?

Answer 48

i. The only body charged by the international union of microbiological societies ii. Purpose: Developing, refining, and maintaining a universal virus taxonomy (classify viruses)

Question 49

International Committee of Taxonomy of Viruses (ICTV) Classification System considers the following for classification of viruses (3)

Answer 49

1. Nature of virus genome and virus genetic diversity 2. Virus replication strategies 3. Virus morphology

Answer 50

1. Order (ends with -virales) Herpesvirales 2. Family (ends with -viridae) Herpesviridae 3. Subfamily (ends with -virinae) Alphaherpesvirinae 4. Genus (ends with -virus) Simplexvirus 5. Species Herpes simplex virus 1 (HSV-1)