Viruses 2

Question 1

What is the eclipse period in virus growth?

Answer 1

The period of time when it appears like there isn’t any virus present because it has infected a cell and been broken down to its components

Question 2

What is the latent period in virus growth?

Answer 2

The period of time up until the first appearance of the virus extracellularly

Question 3

What are the stages of viral replication?

Answer 3

Attachment, penetration, uncoating, genome replication, RNA synthesis, protein synthesis, assembly, release

Question 4

How does a virus attach to its host cell?

Answer 4

By interacting with a physiological receptor on the plasma membrane

Question 5

How does HIV gain access to the cell?

Answer 5

HIV has two proteins gp41 and gp120. The peptide on the end of gp41 is very hydrophobic. The CD4 receptor on the CD4 cell binds to gp120 to capture it. This induces a conformational change which forces the hydrophobic region into the extracellular environment and allows the CCR-5 receptor on the CD4 cell to bind to the gp120 protein. Then the hydrophobic peptide of gp41 inserts into the plasma membrane and drags HIV in closer until the viral envelope merges with the plasma membrane and the genome is released into the cell.

Question 6

What are the two ways which a virus can penetrate a cell?

Answer 6

Viral envelope fusing with the plasma membrane or enter via endocytosis - which then requires exiting from the endosome by exposure of a hydrophobic region or by lysis of the endosome

Question 7

Where do DNA viruses usually replicate?

Answer 7

The nucleus

Question 8

Where do RNA viruses usually replicate?

Answer 8

The cytoplasm

Question 9

What is a DNA virus that doesn’t replicate in the nucleus?

Answer 9

poxvirus

Question 10

What is an RNA virus that doesn’t replicate in the cytoplasm?

Answer 10

influenza virus

Question 11

What kind of proteins are made first by RNA?

Answer 11

non-structural proteins

Question 12

What does a DNA virus use for replication?

Answer 12

The host cell’s DNA dependent DNA polymerase

Question 13

How does a + sense RNA virus replicate?

Answer 13

The genome translates its proteins using host mechanisms and synthesises its own RNA dependent RNA polymerase

Question 14

How does a - sense RNA virus replicate?

Answer 14

By bringing their own RNA dependent RNA polymerase with them into the cell

Question 15

What is class I in the Baltimore Classification?

Answer 15

ds DNA viruses

Question 16

What is class II in the Baltimore Classification?

Answer 16

ss DNA viruses

Question 17

What is class III in the Baltimore Classification?

Answer 17

ds RNA viruses

Question 18

What is class IV in the Baltimore Classification?

Answer 18

+ sense ss RNA viruses

Question 19

What is class V in the Baltimore Classification?

Answer 19

• sense ss RNA viruses

Question 20

What is class VI in the Baltimore Classification

Answer 20

retrovirus - creates DNA from RNA by carrying a reverse transcriptase with it - so that it can integrate with the host cell genome

Question 21

Why does the poxvirus have to carry its own DNA polymerase?

Answer 21

Because it replicates in the cytoplasm

Question 22

How is translation of proteins done by viruses?

Answer 22

By using host cell ribosomes

Question 23

How is post translational cleavage of polyproteins done by viruses?

Answer 23

Usually by virus coded proteases

Question 24

How is glycosylation of envelope glycoproteins done by viruses?

Answer 24

Using the host cell RER and golgi

Question 25

How do non-enveloped viruses assemble?

Answer 25

By spontaneous assembly to form the energy minimised state or by assembly mechanisms

Question 26

How do enveloped viruses assemble?

Answer 26

By budding through the cellular membrane or by secretory pathway of the cell

Question 27

What are the four possible outcomes of the cell after infection by a virus?

Answer 27

Tumor formation, lysis, release without cell death or a latent infection where virus remains in the cell

Question 28

What are cytopathic effects?

Answer 28

Changes seen under the microscope created by viruses

Question 29

What cytopathic effect do adenovirus infected cells have?

Answer 29

Nuclear inclusions

Question 30

What cytopathic effect do reovirus infected cells have?

Answer 30

Cytoplasmic inclusions

Question 31

What are oncogenes?

Answer 31

Genes encoded by the virus which promote growth in the host cell and lead to uncontrolled proliferation

Question 32

How do viruses evolve?

Answer 32

Either by mutation, recombination or reassortment (segmental genome)

Question 33

Why are RNA viruses prone to mutation?

Answer 33

Because their RNA dependent RNA polymerase doesn’t have a proof reading mechanism

Question 34

How does the body halt the infectious process?

Answer 34

• antibodies to block uptake or neutralise progeny
  
  • killing by NK cells, cytotoxic T cells or antibody mediated mechanisms
  • interferon - turns on antiviral mechanisms
  • antiviral drugs that block the replication cycle

Question 35

What is one way in which antiviral drugs are different to antibiotics?

Answer 35

Antiviral drugs are very specific for a certain virus because each virus has a different replication strategy