Virus

Front 1

What are viruses?

Back 1

small, obligate intracellular parasites

Front 2

What is the viral growth cycle absolutely dependent on?

Back 2

the host

Front 3

What are the two components of a virus?

Back 3

1) type of nucleic acid
2) protective coat

Front 4

What is the type of nucleic acid in virus? in cells?

Back 4

1) DNA or RNA but never both
2) DNA and RNA

Front 5

How many proteins do viruses make? in cells?

Back 5

1) few
2) many

Front 6

Does the virus have mitochondria and ribosomes?

Back 6

No

Front 7

How does a virus multiply? a cell?

Back 7

1) exponentially
2) binary fission

Front 8

If you have an envelope what do you always have to have?

Back 8

spike proteins that serve for attachment

Front 9

what type of protective coat does a virus always have and what are the two types?

Back 9

a capsid
1) icosahedral
2) helical

Front 10

What is a single, properly folded polypeptide involved in virus structure?

Back 10

subunit

Front 11

What is the protein shell surrounding the nucleic acid genome?

Back 11

capsid

Front 12

What is the nucleic acid-protein assembly packaged into virion?

Back 12

nucleocapsid

Front 13

What is the lipid bilayer carrying viral glycoproteins?

Back 13

envelope

Front 14

What is the complete infectious viral particle?

Back 14

virion

Front 15

What are the three functions of the viral coat?

Back 15

1) Protects genome from degradation
2)Serves as viral attachment protein to bind to host cell
3) Is often a major site for binding of neutralizing antibodies

Front 16

What can a virus put between the capsid and the envelop?

Back 16

tegument

Front 17

What is needed for the simplest virus?

Back 17

1) viral genome
2) coat protein encoded in the viral genome
3) polymerase which can be encoded for by the host, the virus, or a combination of both

Front 18

What are the two types of viral proteins and which one does the virus need more of?

Back 18

1) structural--> ends up in the viral progeny
2) nonstructural--> catalytic, not in released viral particles
* you need more structural

Front 19

How do we classify viruses?

Back 19

1) Type of nucleic acid, (e.g., RNA vs DNA, ss vs. ds, enveloped)
2) Presence of lipid envelope?
3) Virion morphology
4) Replication Strategy
5) Serological methods – Antibodies to viral components

Front 20

What are the four assays for viruses?

Back 20

1) Cytopathic effect – e.g., “Cell rounding”; multinucleated cells and inclusion bodies
2) Antibody reactivity – e.g., western blotting, immunostaining
3) Viral enzyme activity – e.g., retrovirus reverse transcriptase
4) Molecular Biology Techniques – e.g. PCR
--> the most rapid test and most widely used

Front 21

What are the three phases of the growth curve of a virus?

Back 21

1) eclipse
2) exponential growth (intracellular and extracellular)
3) plateau

Front 22

What are the five universal steps in growth of a virus?

Back 22

1) attachment
2) penetration
3) uncoating
4) gene expression and genome replication
5) assembly and release

Front 23

What are three principals of the host receptor and virus attachment that are important?

Back 23

1) Most of these are known proteins in the host, so the virus doesn’t make a new protein but it is taking advantage of something that is already there
2) The host cell receptor doesn’t always have to be a protein, it can be CHO like sialic acid or a mixture of these two
3) The host cell receptor by itself can not account for tropism which is why do viruses grow in certain tissues or cells and an example is that in the influenza virus that only affects the respiratory tract but sialic acid is all over

Front 24

What are the two ways a virus crosses the plasma membrane?

Back 24

1) Direct fusion of viral envelope with cell membrane (e.g., paramyxoviruses)
2) Endocytosis followed by fusion with endosomal membrane (e.g., influenza virus) or disruption of vesicles (non-enveloped viruses)

Front 25

What is the step that allows access to the nucleic acid?

Back 25

the uncoating step

Front 26

What does the positive strand genome do first?

Back 26

translation

Front 27

What does the negative strand genome do first?

Back 27

transcription

Front 28

How does a virus get the envelope from the host?

Back 28

budding

Front 29

What is the reverse of budding?

Back 29

fusion

Front 30

What is the protein that is required for linking the nucleic acid to the glycoprotein?

Back 30

matrix protein

Front 31

How do you get out of the cell if you are nonenveloped?

Back 31

cell lysis

Front 32

What are the factors that influence viral tropism?

Back 32

1) Presence of cellular receptor - e.g., HIV
2) Presence of cellular enzymes - e.g., proteases for influenza virus.
3) Presence of cellular transcription factors - DNA viruses
4) Type and level of cellular antiviral responses – e.g., interferon
5) Environment of virus-host interaction - pH, temperature

Front 33

What are the possible outcomes of viral infection?

Back 33

1) Little or not apparent (subclinical) - e.g., poliovirus
2) Acute infection - often show cytopathic effect
a) inhibition of host cell macromolecular synthesis
b) cell-cell fusion - syncytia or multinucleated cells
c) inclusion bodies
3) Persistent infections - RNA viruses, often mutants
4) Latent infections - DNA viruses
5) Transformation - oncogenic viruses

Front 34

Which RNA strand virus produces a huge polyprotein?

Back 34

plus strand

Front 35

Which type of virus has reverse transcriptase?

Back 35

retroviruses

Front 36

What are the stages for DNA viruses and what separates them?

Back 36

1) Immediate early
2) early
3) late
The early and late are separated by DNA synthesis

Front 37

What is plus sense RNA?

Back 37

it is the mRNA and it codes for a protein
does translation first

Front 38

What is negative sense RNA?

Back 38

it is the compliment of the mRNA strand and it does not code for a protein
does transcription first into a plus sense then translation can occur

Front 39

What are the main characteristics of a plus strand RNA virus?

Back 39

1) First step is translation by ribosomes to produce a large polyprotein.
2) The viral polyprotein is cleaved by cellular and viral proteases to produce mature proteins (e.g., capsid proteins) needed for growth
3) One of these proteolytic products is viral polymerase which replicates the viral +ve sense RNA to the –ve sense intermediate and to progeny genomes

Front 40

What is the only purpose of the full length negative sense RNA?

Back 40

to serve as a template for positive sense RNA

Front 41

Where do negative and positive sense RNA get their polymerase from?

Back 41

1) Positive sense makes it by translation of the polyprotein
2) Negative sense has to bring it with them when they infect because it is an RNA dependent RNA polymerase and the host does not have it

Front 42

What are the important characteristics of negative sense RNA?

Back 42

1) First step is transcription by viral RNA-dependent RNA polymerase that is brought in by incoming virion
2) New progeny virions must assemble and bud with RNA dependent RNA polymerase.
3) The +ve sense genome RNA only serves as an intermediate template to make more –ve sense genomes

Front 43

Are you envelped and what type of capsid do you have if you are a negative sense RNA?

Back 43

1) It is always enveloped
2) It is always helical

Front 44

Are you envelped and what type of capsid do you have if you are a positive sense RNA?

Back 44

1) It can be either enveloped or not
2) It is usually icosohedral

Front 45

What is a provirus?

Back 45

When reverse transcriptase makes linear ds dna which then integrates into the host chromosome, it is called a pro virus that can sit there for years and at some point it get reactivated then cellular polymerase binds to make two types of rna

Front 46

What are immediate early proteins?

Back 46

Regulatory

Front 47

What are early proteins?

Back 47

enzymes

Front 48

What are late proteins?

Back 48

structural

Front 49

What are two types of genetic changes in viral genomes?

Back 49

1) Mutations
a. Physical or Environmental
b. Polymerase Errors
2) Recombination
a. Reassortment
b. Copy-Choice Recombination
c. Break-Rejoin Recombination

Front 50

How do DNA dependent DNA polyermases repair mistakes?

Back 50

3'-5' exonuclease

Front 51

What is the most important prerequisit to reassortment?

Back 51

1) when you have viruses that have more than one strand of nucleic acid in the virion
2) have to have two different viruses

Front 52

What is antigenic drift in influenza virus?

Back 52

Both HA and NA show drift to create new strains due to accumulation of series of mutations (high polymerase errors). Lifelong immunity to a variant, but human strains recirculate and reappear to infect naïve populations

Front 53

What is antigenic shift?

Back 53

Sudden appearance of virus strains with new antigenic properties due to reassortment of RNA segments (e.g., HA and NA) derived from two different virus strains