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Pathogens > Viruses > Flashcards

Viruses Flashcards

1
Q

Why do viruses not require a large genome?

A

Because they are able to exploit the host genome

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2
Q

What is the nucleocapsid?

A

The complete unit of nucleic acid and capsid

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3
Q

What kind of proteins make up the capsid?

A

Capsomeres

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4
Q

Why are viruses not considered to be truly living?

A

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

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5
Q

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

A

True

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6
Q

Why are viruses often highly specific to their host?

A

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

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7
Q

What are the two main shapes of viruses?

A

Icosahedral

Helical

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8
Q

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

A

Complex

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9
Q

Do cytolytic viruses usually have an envelope?

A

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

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10
Q

On what factors can a virus be classified?

A

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

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11
Q

What type of nucleic acid can a virus have?

A

dsDNA
ssDNA
dsRNA
ssRNA

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12
Q

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

A

Retroviruses

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13
Q

What is a virion?

A

The complete extracellular form of a virus

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14
Q

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

A

Neuraminidase

Haemagluttinin

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15
Q

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

A

Neuraminidase

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16
Q

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

A

The host cell cannot form mRNA from RNA

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17
Q

How can a virus enter a host?

A 
Skin / Mucosa (abrasions, inoculation, insect or animal bite)
Respiratory tract
GI tract
Conjunctiva
Genital Tract
18
Q

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

A

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

19
Q

During virus replication what proteins are produced first?

A

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

20
Q

All viruses need transcription to occur. T/F?

A

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

21
Q

Why can viruses mutate so rapidly?

A

RNA polymerase is highly innacurate

22
Q

What is a viral quasispecies?

A

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

23
Q

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

A

Group VI

24
Q

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

A

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

25
Q

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

A

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

26
Q

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

A

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

27
Q

How does nucleic acid replication of retroviruses work?

A

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

28
Q

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

A

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.

29
Q

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

A

True

30
Q

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

A

Antigenic variation

31
Q

What is antigenic drift?

A

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

32
Q

What is antigenic shift?

A

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

33
Q

How is HPV transmitted?

A

Mucosal abrasions

34
Q

How is hepatitis B transmitted?

A

Inocculation

35
Q

How is rabies transmitted?

A

By insect or animal bite

36
Q

How is influenza transmitted?

A

Through the respiratory tract

37
Q

How is poliovirus transmitted?

A

GI tract

38
Q

How is adenovirus type 8 transmitted?

A

Conjuctiva

39
Q

How is herpes simplex virus transmitted?

A

Through the genital tract

40
Q

What factors increase the rate of antigenic drift?

A

Strong host immune response

Long duration of epidemic

41
Q

Why are viruses a particular medical problem?

A

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

Pathogens (3 decks)

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