1 - Intro to Viruses

Question 1

Viruses

Answer 1

• Inert outside living host
• Cause infection
• Most do not cause disease in humans
• We carry viral genomes as part of our own genetic material (endogenous retroviruses)

Question 2

Four traits viruses are defined by

Answer 2

• Virions
• Capsomeres
• Assembly
• Capacity to evolve

Question 3

Virion

Answer 3

Infectious extracellular stage of obligate intracellular viruses`

Question 4

Capsomeres

Answer 4

• All viruses encode atleast one
• Cover and protect the nucleic acid in a virion

Question 5

Assembly

Answer 5

Cells infected by virus synthesise the component parts of virion, and then the parts spontaneously assemble into new virions

Question 6

Capacity to evolve

Answer 6

Because the minimum composition of viruses is nucleic acids and capsomeres, viral populations can change through typical evolutionary processes (e.g. selective pressures)

Question 7

Obligate intracellular parasites

Answer 7

• Require host cells to multiply
• No machinery for protein synthesis and energy production

Question 8

Capsid

Answer 8

• The protein coat of capsomeres that surrounds the nucleic acids
• May be spherical or helical

Question 9

How are virions separated

Answer 9

• Into two classes based on whether they have an external layer consisting of a proteinaceous lipid bilayer
• Enveloped virions have a lipid bilayer
• Naked viruses do not

Question 10

Spherical capsids

Answer 10

• Icosahedrons (approximate the volume of a sphere yet are constructed from
  repeated subunits)
• Spherical capsids are somewhat rigid, helical capsids can be rigid or flexible

Question 11

Bacteriophages

Answer 11

Combine the icosahedral and helical elements, so that their heads, full of nucleic acids, are icosahedral but their tails are helical assemblages of specialized tail proteins.

Question 12

Nucleocapsid

Answer 12

The nucleic acid genome and capsomeres are so intimately associated

Question 13

Example of virus that lack clearly defined capsids

Answer 13

Poxviruses

Question 14

Most successful vaccine

Answer 14

HPV (via virus like particles)

Question 15

Examples of RNA viruses

Answer 15

• Coronaviruses
• Flaviviruses
• Retroviruses

Question 16

Examples of DNA viruses

Answer 16

• Adenoviruses
• Herpesviruses
• Poxviruses

Question 17

Baltimore classification

Answer 17

Viruses can be classified according to the ways they synthesise and use mRNA

Question 18

Central dogma and importance of mRNA

Answer 18

• DNA –> RNA –> Protein
• Cellular genes are encoded in dsDNA from which mRNAs are produced
  to direct the synthesis of protein.
• Therefore all viruses must direct the synthesis of mRNA to produce proteins

Question 19

Quasispecies

Answer 19

Upon infection with an RNA virus viral replication leads to a mutant spectrum of related genomes (quasispecies)

Question 20

Size of viruses

Answer 20

• Many viruses are less than 200 nm (10^-9 m) in diameter (spherical
  viruses) or length (helical viruses)
• Too small to be seen by light microscopy

Question 21

Animal cells in culture

Answer 21

• Form confluent carpets (cells introduced into culture attach to and spread out until cells are touching one another without overlapping)
• Contact inhibition prevents further population increase

Question 22

Example of virus induced cytopathic effects (CPE)

Answer 22

• Cause infected cells to round up and detach from the tissue flask as they die
• Syncytia (large, multinucleate cells)
• Cause abnormal internal structures visible when the host cells are stained (e.g. inclusion bodies)
  -Transformed cancerous cells grown on top of each other instead of responding to contact inhibition

Question 23

Inclusion bodies

Answer 23

Sites of viral gene expression, genome replication, or assembly

Question 24

Methods of culturing viruses

Answer 24

• In animal and human cells
• In embryonated chicken eggs

Question 25

First step of SARS-CoV-2 cell entry

Answer 25

Binding of spike protein to receptor (ACE2)

Question 26

What are classical taxonomic categories based on

Answer 26

• Disease they cause
• Symptoms of disease they cause
• Structure
• Phenotype
• Evolutionary relatedness