Introduction to Virology

Question 1

Are viruses living?

Answer 1

No, they lack the essentials of life

Question 2

Which essentials of life do viruses display?

Answer 2

Protecting contents from external environment
Evolve by natural selection

Question 3

Which essentials of life do viruses not display?

Answer 3

Ability to take up energy and make use of it
Transport of cell; into cell; within cell
Reproduction of self

Question 4

Why are viruses obligate parasites?

Answer 4

They must have a host cell to reproduce

Question 5

Where are the highest mutation rates found and why?

Answer 5

In the smallest genomes
They are less likely to correct mistakes in DNA replications due to less enzymes

Question 6

What does a virus need?

Answer 6

To be able to enter a host cell
Have the host cell replicate the viral genetic material
Have the host cell transcribe and translate the viral genes

Question 7

What can happen once all the virus components are made?

Answer 7

The infectious viral particle, the virion, can be assembled

Question 8

What was the fatality rate of yellow fever?

Answer 8

20%

Question 9

How is yellow fever transmitted?

Answer 9

Mosquitos

Question 10

What are River’s postulates?

Answer 10

1. Isolation of virus from diseased hots
2. Cultivation of virus in host cells
3. Proof of filterability (confirms small size)
4. Production of a comparable disease when used to infect experimental animals
5. Re-isolation of the same virus from the infected host
6. Detection of a specific immune response to the virus

Question 11

What is the general strategy that all viruses follow?

Answer 11

They package their genomes into a particle that mediates transmission from host to host

A virus genome contains the information for an infectious cycle within a susceptible permissive cell

All viruses are able to establish themselves in a host population so that their survival is ensured

Question 12

What did Hershey and Chase prove?

Answer 12

DNA is the genetic materail

Question 13

How do viruses protect their genetic material?

Answer 13

Protected by capsids
Resistant to proteases, heat, or temperature extremes
Uses as few proteins as possible

Question 14

Which viruses are more susceptible to the environment?

Answer 14

Enveloped viruses

Question 15

What does the arrangement of nucleic acid and protein cost in tobacco mosaic virus look like?

Answer 15

The RNA assumes a helical configuration surrounded by the protein capsid
The information for assembly is contained within the protein-structure itself
This process is called self-assembly

Question 16

Why do capsids use as few proteins as possible?

Answer 16

Makes syntthesis easier

Question 17

What is the viral lifecycle?

Answer 17

Attachment = use a variety of receptors

Penetration = crossing the membrane

Utilization = host cell proteins/enzymes needed for replication, transcription, translation

Biosynthesis = synthesis of proteins

Assembly = progeny particles are produced

Question 18

What is the life cycle of an enveloped RNA virus like?

Answer 18

The viral envelope membrane fuses with the host cell membrane to allow entry
RNA is transcribed and replicated using viral enzymes
The virus can leave the cell by budding off which takes some of the host cell membrane with it

Question 19

How does the membrane help the virus hide from our immune system?

Answer 19

It is of host origin
Contains host proteins

Question 20

Why is viral growth exponential?

Answer 20

Viruses synthesize progeny de novo and release a large number at once

Question 21

How many poliovirus particles are released in 24 hours?

Answer 21

1-50,000

Question 22

How is viral titre determined?

Answer 22

A dilution is mixed with bacteria and melted agar
Pour onto an agar plate
Phage plaques make holes in the lawn

Question 23

What is the unit used to report virus titre?

Answer 23

Plaque-forming units/mLd

Question 24

What is viral classification based on?

Answer 24

The nature of the genetic material
Symmetry of the capsid
Presence of an envelope, dimensions