Viruses In general

Question 1

Summary of Viruses

Answer 1

• Obligate intracellular parasites
• Every virus has a nucleocapsid containing genetic material (RNA or DNA) and protein
• Some viruses are enveloped (coated with host cell membrane). These are released from the cell through budding.
• Human viruses have a diameter of 30-300 nm
• Viruses are classified by genome, virus particle structure, and replication strategy

Question 2

Poxiviridae

Answer 2

Virus: smallpox, vaccinia
Genome: dsDNA
Enveloped
**Replicates in the cytoplasm

Question 3

Filoviridae

Answer 3

Virus: Marburg, Ebola
Genome: (-) ssRNA
Enveloped

Question 4

Arenaviridae

Answer 4

Virus: Lassa, Junin, Machupo, LCMV
Genome: segmented ambisense ssRNA
Enveloped

Question 5

Flaviviridae

Answer 5

Virus: Yellow fever, Dengue fever, West Nile, JE, TBE, Hep C
Genome: (+) ssRNA
Enveloped

Question 6

Togaviridae: Alphavirus

Answer 6

Virus: EEE, VEE, WEE, Sindbus, Semliki Forest, Chikungunya
Genome: (+) ssRNA
Enveloped

Question 7

Orthomyxoviridae

Answer 7

Virus: Influenza
Genome: (-) ssRNA 8 segments
Enveloped
**Replicates in the nucleus
Surface proteins HA and NA. (HA: viral attachment and fusion, NA: cleavage of sialic acid residues on cell receptors and virion glycoproteins)

Question 8

Bunyaviridae: Hantavirus

Answer 8

Virus: Hantavirus
Genome: (-) ssRNA 3 segments
Enveloped

Question 9

Bunyaviridae: Phlebovirus

Answer 9

Virus: Rift valley fever, Crimean Congo
Genome: (-) ssRNA 3 segments (ambisense)
Enveloped

Question 10

Adenovirus

Answer 10

Virus: Adenovirus 5
Genome: dsDNA
Non-enveloped

Question 11

Picornaviridae

Answer 11

Virus: Poliovirus, Rhinovirus, Hep A
Genome: (+) ssRNA
Non-enveloped

Question 12

Retroviridae

Answer 12

Virus: Murine leukemia virus, HIV
Genome: (+) ssRNA **two copies per virion
Enveloped
**replicates in nucleus via reverse transcriptase and integrase

Question 13

Coronaviridae

Answer 13

Virus: SARS
Genome: (+) ssRNA
Enveloped

Question 14

Reoviridae

Answer 14

Virus: Rotavirus, Blue tongue, Reovirus
Genome: segmented dsRNA
Non-enveloped

Question 15

Hepadnaviridae

Answer 15

Virus: Hep B
Genome: circular dsDNA
Enveloped

Question 16

Deltaviridae

Answer 16

Virus: Hep Delta
Genome: (-) ssRNA
Enveloped

Question 17

Calciviridae

Answer 17

Virus: Hep E
Genome: (+) ssRNA
Non-enveloped

Question 18

Rhabdoviridae

Answer 18

Virus: Rabies virus
Genome: (-) ssRNA
Enveloped

Question 19

Paramyxovirus

Answer 19

Virus: Measles, Mumps, Parainfluenza, Respiratory Syncytial Virus
Genome: (-) ssRNA
Enveloped
F protein is found on all paramyxoviruses and initiates virus-cell envelope fusion when cleaved

Question 20

(+) ssRNA Viruses

Answer 20

• Use their mRNA as their genome
• Considered infectious nucleic acid
• Encodes for its own RNA polymerase and therefore doesn’t need to bring its own

Question 21

(-) ssRNA Viruses

Answer 21

• Use a complementary copy of their mRNA as their genome

- They NEED a biologically active enzyme in the virion to make (+) mRNA (RNA Polymerase). This is brought with them

Question 22

Retroviruses

Answer 22

• Are exceptions to the (+/-) rule
• The retrovirus + strand is not the mRNA
• ssRNA diploid gene is the template for dsDNA (provirus) synthesis via a virion associated RNA-dependent DNA polymerase (reverse transcriptase)
• The provirus randomly integrates with the host DNA. Host cell DNA-dependent RNA polymerase II transcribes the provirus DNA into viral mRNAs and into full length virion genomic RNAs

Question 23

What is a provirus?

Answer 23

A dsDNA virus genome that has integrated itself into the DNA of a host. Retroviruses use this as an mRNA template.

Question 24

RNA vs DNA polymerases

Answer 24

• RNA do NOT require primers to initiate RNA replication

- DNA REQUIRE a primer.

Question 25

What is the difference between Paramyxoviridae and Orthomyxoviridae?

Answer 25

Para: unsegmented ssRNA
- mRNA synthesis in cytoplasm
- reassortment is rare (why we get one vaccine)
Ortho: segmented ssRNA
- mRNA synthesis in nucleus
- reassortment is frequent (why you get a vaccine every year)

Question 26

What are the viruses that cause Gastroenteritis and their genomes? Are these viruses likely to be naked or enveloped?

Answer 26

Rotaviruses: dsRNA (segmented)
Adenoviruses: dsDNA (linear)
Norwalk virus: RNA
Calciviruses: (+) ssRNA
Astroviruses: (+) ssRNA

• likely to be naked b/c if they had an envelope it would dissolve in the stomach rendering the virus ineffective

Question 27

What are the general steps involved in virus replication?

Answer 27

CAPUMAR

• Contact
• Attachment
• Penetration
• Uncoating
• Macromolecular synthesis (mRNA, protein, nucleic acid)
• Assembly
• Release