Virology

Question 1

Define virus

Answer 1

genetic element that cannot replicate
independently of a living (host) cell

Question 2

Where do virus particles live?

Answer 2

They exist outside the host

Question 3

Viral genomes are either DNA or RNA, what shapes are they

Answer 3

some circular but mostly linear

Question 4

Name some virus classifications (based off the hosts they infect)

Answer 4

bacteriophages
Archaeal viruses
* Animal viruses
* Plant viruses

Question 5

What is the capsid structure

Answer 5

Its the protein shell that surrounds the
genome of a virus particle, its made of protein molecules around the nucleic acid

Question 6

What is the capsomere?

Answer 6

subunit of the capsid

Question 7

What is the name of the type of virus that contains additional layers around the nucleocapsid

Answer 7

Enveloped virus

Question 8

What are the two symmetrical ways that nucleocapsids are constructed?

Answer 8

Helical and Icosahedral

Question 9

What shapes are Helical and Icosahedral and give an example of a virus

Answer 9

Helical: rod-shaped viruses (tobacco mosaic)
Icosahedral: spherical viruses (HPV)

Question 10

Name the enzymes critical to infection

Answer 10

Lysozyme
Nucleic acid polymerases
Neuraminidases

Question 11

What is one way to measure
virus infectivity

Answer 11

Plaque assay

Question 12

What are plaques

Answer 12

They are clear zones that develop lawn of host cells
Each plaque results from infection
by a single virus particle

Question 13

How are plaque assays done

Answer 13

1)Mixture containing
molten top agar,
bacterial cells, and
diluted phage
suspension is poured onto agar plate
2) let solidify and incubate
3)Lawn of host cells have been grown

Question 14

Is the plaque assay efficient and why?

Answer 14

No
The number of plaque-forming units is almost always lower than direct counts by
electron microscopy
Inactive virions

Question 15

What are the phases of viral replication

Answer 15

1) Attachment (adsorption) of the virus to a
susceptible host cell
2) Entry (penetration) of the virion or its nucleic acid
3) Synthesis of virus nucleic acid and protein by cell metabolism as redirected by virus
4) Assembly of capsids and packaging of viral genomes into new virions
5)Release of mature virions from host cell

Question 16

What does the attachment of virion to host cell require

Answer 16

It needs complimentary receptors on the surfaces of susceptible host and its infecting virus

Question 17

What does the receptors on the virion include

Answer 17

proteins,
carbohydrates, glycoproteins, lipids

Question 18

Permissive cell definition

Answer 18

host cell that allows the complete
replication cycle of a virus to
occur

Question 19

What are some mechanisms used to diminish viral infections

Answer 19

RNA interference
CRISPR

Question 20

What kind of virus is the DNA destruction system useful against?

Answer 20

double-stranded
DNA viruses

Question 21

What are class I and class II of viruses

Answer 21

1: double-stranded (ds) DNA
viruses
2: single-stranded (ss) DNA
viruses

Question 22

What are class III and class IV/ V of viruses

Answer 22

3: dsRNA
4 & 5:ssRNA

Question 23

What are class VI and class VII of viruses

Answer 23

6:retroviruses
7:dsDNA viruses that
replicate through an RNA intermediate

Question 24

Retrovirus definition and give an example

Answer 24

animal viruses responsible for
causing certain types of cancers and acquired immunodeficiency syndrome e.g. AIDS

Question 25

When are early proteins synthesised

Answer 25

synthesized soon after
infection

Question 26

What type of protein is necessary for replication of virus nucleic acid

Answer 26

Early proteins

Question 27

When are late proteins synthesised? And what do they include?

Answer 27

Synthesized later
* Include proteins of virus
coat

Question 28

What are the 2 viral life cycles?

Answer 28

Virulent mode and Temperate mode

Question 29

Virulent mode definition

Answer 29

viruses lyse host cells after
infection

Question 30

Temperate mode definition

Answer 30

viruses replicate their
genomes in tandem
with host genome and
without killing host

Question 31

What type of life cycle can undergo a stable genetic
relationship within the host and can also kill cells through lytic cycle

Answer 31

Temperate

Question 32

What are some Consequences of Virus Infection in Animal Cells

Answer 32

Persistent infections (release of virions from
host cell does not result in cell lysis)
Latent infections:( delay between infection
by the virus and lytic events)
Transformation: (conversion of normal cell
into tumor cell)
Cell fusion ( two or more cells become one
cell with many nuclei)

Question 33

What do retroviruses contain?

Answer 33

Enveloped viruses
Contain a reverse transcriptase
Virion contains specific tRNA
molecules

Question 34

What is the Process of Replication of a Retrovirus

Answer 34

1) enters the cell
2) Removes the virion envelope at the membrane
3) Reverse transcription of one of the two
RNA genomes
4) Integration of retroviral DNA into host
genome
5) Transcription of retroviral DNA
6) Assembly and packaging of genomic RNA
7) Budding of enveloped virions; release
from cell

Question 35

Defective virus definition

Answer 35

viruses that are parasitic on other viruses ( they need a helper virus to function)

Question 36

Satellite virus definition

Answer 36

defective viruses for which no intact version exists; rely on unrelated viruses as helpers

Question 37

Viroid definition

Answer 37

infectious RNA
molecules that lack a protein
coat