Viruses

Question 1

Why do viruses not require a large genome?

Answer 1

Because they are able to exploit the host genome

Question 2

What is the nucleocapsid?

Answer 2

The complete unit of nucleic acid and capsid

Question 3

What kind of proteins make up the capsid?

Answer 3

Capsomeres

Question 4

Why are viruses not considered to be truly living?

Answer 4

They are metabolically inert and can only replicate after infecting a host and parasitising the host’s ability to transcribe and translate genetic information.

Question 5

Viruses which are enveloped are susceptible to environmental factors. T/F

Answer 5

True

Question 6

Why are viruses often highly specific to their host?

Answer 6

Because the virus must have surface proteins which allow it to bind to receptors on its host cell

Question 7

What are the two main shapes of viruses?

Answer 7

Icosahedral

Helical

Question 8

What is the name of viruses which do not conform to the two main shapes?

Answer 8

Complex

Question 9

Do cytolytic viruses usually have an envelope?

Answer 9

No - viruses which bud off from the host cell usually have an envelope

Question 10

On what factors can a virus be classified?

Answer 10

Morphology
Type of nucleic acid
Method of RNA transcription
Type of disease that they cause

Question 11

What type of nucleic acid can a virus have?

Answer 11

dsDNA
ssDNA
dsRNA
ssRNA

Question 12

What is the name of the type of virus which have single stranded RNA which they then convert to DNA during their replication process?

Answer 12

Retroviruses

Question 13

What is a virion?

Answer 13

The complete extracellular form of a virus

Question 14

What are the two main proteins of the envelope of the influenza virus?

Answer 14

Neuraminidase

Haemagluttinin

Question 15

What is the name of the enzyme which the influenza virus carries in order to allow release from the infected cell?

Answer 15

Neuraminidase

Question 16

Why must viruses which contain RNA always have their own replicase?

Answer 16

The host cell cannot form mRNA from RNA

Question 17

How can a virus enter a host?

Answer 17

Skin / Mucosa (abrasions, inoculation, insect or animal bite)
Respiratory tract
GI tract
Conjunctiva
Genital Tract

Question 18

How do naked viruses enter a host cell compared to how enveloped viruses enter the host cell?

Answer 18

Both start by binding go a specific receptor on the host cell surface
Naked viruses enter animal cells by endocytosis
Enveloped viruses enter animal cells by membrane fusion

Question 19

During virus replication what proteins are produced first?

Answer 19

Virus proteins required for the replication of viral nucleic acids are produced first.

Question 20

All viruses need transcription to occur. T/F?

Answer 20

False - if viruses contain single stranded positive sense RNA then this can be used immediately as the mRNA template

Question 21

Why can viruses mutate so rapidly?

Answer 21

RNA polymerase is highly innacurate

Question 22

What is a viral quasispecies?

Answer 22

A group of viruses related by similar mutation or mutations that compete within a highly mutagenic environment

Question 23

Which group is a retrovirus classified under in the holmes classification system?

Answer 23

Group VI

Question 24

What are the six steps of the processes of viral infection of host and replication?

Answer 24

Adsorption - virus binds to host cell
Penetration - virus injects its genome into the host cell
Viral genome replication - using host cell machinery
Assembly - viral components and enzymes are produced and begin to self-assemble
Maturation - viruses fully develop
Release - newly produced virus is expelled from the cell

Question 25

Once a virus has penetrated a cell, how is it uncoated and what does this achieve?

Answer 25

Uncoating is done by the removal of the protein coat by degrading enzymes allowing the release of viral nucleic acid into the cell

Question 26

If single stranded RNA is described as 'negative sense what does this mean?

Answer 26

The base sequence on the RNA is not the same as that required for translation so transcription must occur

Question 27

How does nucleic acid replication of retroviruses work?

Answer 27

Retroviruses have positive sense single strand RNA which is converted to negative sense DNA by reverse transcriptase. The negative sense DNA strand is the transcribed by the host into mRNA

Question 28

What happens during the release stage to give viruses their envelope?

Answer 28

The envelope proteins and glycoproteins translated from viral mRNA are inserted into areas of the host cell membrane. The new nucleocapsids associate with the host membrane at areas where these proteins have been inserted, The new virus particles then bud off from the host cell and the hist membrane with associated viral proteins becomes the new envelope around the nucleocapsid.

Question 29

Some viruses can transform a cell from a healthy cell to a tumour or cancer cell. T/F?

Answer 29

True

Question 30

What method do viruses have which allow them to evade the 'memory' of a host immune system?

Answer 30

Antigenic variation

Question 31

What is antigenic drift?

Answer 31

It is when mutations accumulate within the genes that code for antibody-binding sites

Question 32

What is antigenic shift?

Answer 32

When two or more different strains of a virus combine to form a new subtype which has a mixture of surface antigens from the original strains. It can result in the creation of new viral pathogens

Question 33

How is HPV transmitted?

Answer 33

Mucosal abrasions

Question 34

How is hepatitis B transmitted?

Answer 34

Inocculation

Question 35

How is rabies transmitted?

Answer 35

By insect or animal bite

Question 36

How is influenza transmitted?

Answer 36

Through the respiratory tract

Question 37

How is poliovirus transmitted?

Answer 37

GI tract

Question 38

How is adenovirus type 8 transmitted?

Answer 38

Conjuctiva

Question 39

How is herpes simplex virus transmitted?

Answer 39

Through the genital tract

Question 40

What factors increase the rate of antigenic drift?

Answer 40

Strong host immune response | Long duration of epidemic

Question 41

Why are viruses a particular medical problem?

Answer 41

A single infection can produce thousands of progenies Rapid exchange of genetic material leads to high mutation rate and divergence, making vaccine difficult to make against viruses