M: Virology 1 - Week 11 Flashcards by B H

What is a virus? (2)

An infectious, obligate intercellular molecular parasite containing a DNA or RNA genome that is packaged into a virion particle from host to host

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What do viruses require for replication?

Totally dependent on a living host cell for propagation and replication

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What type of genome do viruses have? (2)

DNA or RNA genome

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Is the viral genome single or double stranded?

Can be either

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How big are viruses compared to bacteria? What about compared to eukaryotic cells?

Small compared to bacteria
Very small compared to eukaryotic cells

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How does virus receptor-binding compare between viruses?

Specific: each virus has a receptor-binding/virus-attachment protein for initial contact with host cell receptors and entry into target cell

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How are new virus particles assembled?

Are assembled from new viral components synthesised in infected cells

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What is the information contained in viral genomes used for?

Viral genomes contain all the information to initiate and complete an infectious cycle

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What are the 2 phases of a virus?

Virion
Infected cell

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Define Virion

The complete, infective form of a virus outside a host cell, with a core of RNA or DNA that is either single or double stranded, and a capsid

(Also: an archer from fire emblem awakening. A very posh and flamboyant man)

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What is a capsid?

A protective protein coat for the genome

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Are viruses cells? Explain

No!
Viruses contain NO ribosome machinery for protein synthesis

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What is the size range for viruses? What is noteworthy about this?

Range from 20nm to 250-300nm

These sizes are too small to see on a light microscope. Need an electron microscope to view

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What is necessary for sucessful electron microscopy of viruses? (2)

Require pure particles with proven infectivity
Negative staining also necessary

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What can you use for negative staining of viruses in electron microscopy?

Potassium phosphotungstate

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What does X-ray crystallography of viruses require?

Computer for image reconstruction of virus

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What does the virion sometimes posses?

An envelope made of cell membrane modified to contain virus proteins

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What are capsomers?

Clusters of capsid protein subunits

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What is an envelope?

A lipoprotein membrane surrounding either nucleocapsid or capsid

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What is a nucleocapsid?

The proteins most closely assembled onto the viral nucleic acid (sometimes this IS the capsid protein)

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Where are the phospholipids of the envelope derived from?

From the host cell membrane

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What codes the glycoproteins of the virus envelope?

Virus-encoded

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What is a virus matrix?

A layer of protein that connects the capsid to envelope glycoproteins

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Name the 2 different forms of capsid symmetry

Icosahedral capsid
Helical capsid

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What are the 3 different axes for the icosahedral symmetry

Twofold axis Threefold axis Fivefold axis

Provide 3 examples of viruses with icosahedral symmetry

Adenovirus Herpesvirus Papillomavirus

What 2 conditions do adenoviruses cause?

Respiratory illness Conjunctiva

How many species of herpesvirus are there? Name 4

8 HSV Cytomegalovirus Varicella zoster EBV

What does papillomavirus cause?

causes warts. These warts can become malignant (on genitals)

Describe the architecture of helical capsid symmetry. What does it look like?

A planar net of identical protein subunits wraps around the nucleic acid to form a protective layer

Provide 2 examples of viruses with nucelocapsids of helical symmetry

Mumps virus Influenza virus

What symmetry do poxyviruses have?

They are an exception to the rule and have neither icosahedral nor helical symmetry. Their symmetry is COMPLEX

Which virus is the largest?

Poxyviruses are the largest

How many different proteins are present in the poxyvirus virion?

Over 100

What symptom does rotavirus infection typically cause?

Diarrhea (in children)

Is Rotavirus considered hardy or sensitive? Why?

Hardy. It survives passage through the gut and even sewage treatment. - this is because it has 2 protein layers (outer and inner capsid) that protect the inner nucleic acid

What is meant by the term "Naked Virus"?

A virus that has no envelope

Does rotavirus have an envelope?

No. It is a naked virus

Do viruses with envelopes or naked viruses kill the cell upon leaving?

Naked viruses kill the cell. The envelope allows the virus to leave without killing the cell.

Is influenza an enveloped virus or naked virus?

enveloped virus

What is the envelope for the influenza virus derived from?

derived from the plasma membrane of cells

Which kind of virus is more resistant to environmental conditions: enveloped virus or naked virus? Why?

Naked virus. Lipid envelops are quite fragile and sensitive to denaturation (heat/cold/pH) they are more likely to be denatured and then the virus loses infectivity. This is not the case with non-enveloped/naked viruses.

What forms can the genome of viral nucleic acid be found in? (4)

may be: S.S DNA D.S DNA S.S RNA D.S RNA s.s = single-stranded. d.s = double-stranded

Which kinds of viral nucleic acid genome can form complex structures? (2)

ss DNA and ss RNA

What are virus families classified by? (3) (technically 8 I guess actually)

Kind of nucleic acid genome, and arrangement (order) or genes Morphology of the virion (capsid symmetry, +/- envelope, size, appearance) Strategy of viral replication

What does the family name for viruses end in? How are virus family names written?

-viridae written in italics

Define genus

a group of species sharing certain common characteristics

What are genera classified by? (4) (note: genera = plural of genus)

size of genome and sequence differences number and size of proteins serological reactivity host range and disease produced (sometimes)

What do the names for genera end in?

-virus (e.g. lentivirus)

Are icosohedral viruses enveloped or naked?

Can be either

Are helical viruses enveloped or naked?

All of them are enveloped

What does it mean for a viral RNA genome to be "positive sense?"

Positive-sense (5' to 3') viral RNA signifies that a particular viral RNA sequence may be directly translated into the desired viral proteins. Therefore, in positive-sense RNA viruses, the viral RNA genome can be considered viral mRNA, and can be immediately translated by the host cell.

Which viruses contain a virion polymerase: viruses with a positive sense genome or viruses with a negative sense genome? Why

Viruses with a negative-sense genome contain a virion polymerase positive-sense genomes can act as mRNA to directly synthesise proteins without the help of a complementary RNA intermediate - i.e they don't need a virion polymerase

How are retroviruses considered the exception to the rule for virion polymerase?

They contain virion polymerase despite being a positive-sense genome

What is virion polymerase?

An enzyme capable of replicating the genome (a.k.a. RNA-dependent RNA polymerase: catalyses the replication of RNA from an RNA template)

Out of the viruses we should know about, which is the only virus that is double stranded?

Reoviridae

Where do enteric viruses primarily replicate?

Intestinal tract

How are enteric viruses acquired?

ingestion (e.g. rotavirus, calicivirus, astrovirus, some adenoviruses)

Where do respiratory viruses primarily replicate?

respiratory tract

How are respiratory viruses acquired?

inhalation of droplets

What do Arboviruses infect? How are they transmitted?

infect insects and are transmitted by bite to mammals

Name 4 arboviruses

orbivirus most bunyaviruses flaviviruses togavirus

How are sexually transmitted viruses transmitted? (lol)

sexually

What is the principle target for hepatitis viruses?

Liver

How are the 5 hepatitis viruses spread? (2)

Hep A + E: spread by enteric route Hep B + C + D: spread by blood or sexually

True or False: Hepatitis viruses all belong to the same taxonomic family

False. Each has a different taxonomic family

Why can a laboratory diagnosis be useful for a virus? (3)

Useful for: Deciding treatment options (some viruses are slow/persistent, so tx useful) Public Health measures Surveillance

Name 3 general treatment options that could be implemented for a virus

chemotherapy passive immunization abortion (extreme)

Name 2 public health measures that could be taken against a virus

Blood bank screening (for HIV, HBV, HCV) Contact monitoring/treatment

Name 5 methods of viral detection

Direct visualisation by electron microscopy Viral cultivation Viral protein (antigen) detection Host serological response Viral gene detection

What method of viral detection was considered the gold standard? (15 years ago)

Viral cultivation

What are the disadvantages of viral cultivation? (3)

Some viruses have NO culture system (e.g. HCV) so can't be cultured Slow Result often too late to impact on treatment

What determines what clinical samples you should take for virus identification?

samples taken depends on the disease syndrome (e.g. if eye, take tear/conjunctival swab)

How are clinical samples for viral identification transported to the laboratory?

samples are refrigerated or frozen in buffered "transport medium" for transfer to the lab

How well do enveloped viruses survive outside host cells?

poorly

What are 3 techniques we can use to help preserve viral infectivity for cultivation?

Use low temperature Freeze drying (some viruses) Buffered transport medium

What temperature should we store viruses in for a day or so? (to preserve viral infectivity)

4 degrees celsius

What temperature should we store viruses in for long term storage? (to preserve viral infectivity)

-70 degrees celsius

What temperature should we store viruses in for permanent storage? (to preserve viral infectivity)

-196 degrees celsius

When storing viruses to preserve viral infectivity, what should be avoided?

avoid repeated freezing and thawing

How does freeze-drying a virus work?

dehydration of a frozen suspension under vacuum

How often is direct visualisation by EM used? Name an instance

Mostly not used. Can be used for certain cases such as high concentration of rotavirus

Name 3 virus cell cultures we can have

Animal culture (e.g. suckling mice) Embryonated egg culture Mammalian cells

What types of mammalian cells are used in cell culture? (3)

Primary cells: prepared from animal tissue Diploid cell lines: have limited lifespan in culture "Transformed" or "continuous" cell lines: can be passaged indefinitely in vivo

What are inclusion bodies?

Inclusion bodies represent accumulated viral proteins at the site of virus assembly

What type of inclusions do adenovirus-infected cells present with?

nuclear inclusions

What type of inclusions do reovirus-infected cells present with?

cytoplasmic inclusions

What happens to measles virus during replication?

fusion of neighbouring cells and the formation of multi-nucleated cells or syncytia

Name 2 serological assays for viruses. Do they have high sensitivity or high specificity? (2)

Antigen capture assay (HIV p24 assay) = High sensitivity Anti-viral antibody assay (HIV "western blot") = High specificity

Which serological assay is considered the principle diagnostic for HIV infection?

Antigen capture assay (HIV p24 assay)

Describe the following features of infectivity/serology assays: - speed - sensitivity of viral antigen detection

Generally slow High sensitivity (therefore can result in false positives)

Describe a methodology for more rapid detection of viral nucleic acids (6)

Southern blot for viral DNA Northern blot for viral DNA PCR for DNA Reverse-transcriptase PCR for RNA Viral nucleic acid sequencing DNA microarray technology

How deep is viral nucleic acid sequencing?

Deep sequencing of everything that is there

What is the sensitivity and specificity of a PCR assay?

High for both

In regards to a PCR assay: - how fast? - how much sample? - how cheap? - how easily adaptable? - is it automated?

Very fast Low amount sample Cheap Easily adapted yes its automated