Lecture 8: Virology Flashcards

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1
Q

Describe Charles Chamberland’s contributions towards microbiology

A

1) Charles Chamberland (1851-1908) worked with Louis Pasteur, he developed Chamberland’s Porcelain Bacterial Filter which filtered out most microbes (bacteria, some viruses).
2) Marketed it as a water filter.

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2
Q

List the properties of viruses (6)

A

1) Viruses are filterable agents; small size allows them to pass through filters designed to retain bacteria
2) Viruses are obligate intracellular parasites
3) Viruses cannot make energy or proteins independently of a host cell
4) Viral genomes may be RNA or DNA but not both
5) Viruses have a naked capsid or an envelope morphology
6) Viral components are assembled and do not replicate by division

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3
Q

In order to be a successful pathogen, what 5 things must be true about the virus?

A

1) Viruses are not living
2) Viruses must be infectious to endure in nature
3) Viruses must be able to use host cell process to produce their components
4) Viruses must encode any required processes not provided by the host cell
5) Viral components must self-assemble

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4
Q

1) How big are viruses?
2) Are viruses diverse?
3) What does a complete virus particle or virion consist of?

A

1) Viruses range in size from about 10 to 400 nm in diameter (big range)
2) Very diverse
3) A complete virus particle or virion consists of one or more molecules of DNA or RNA enclosed in a coat of protein. The virion is the entire viral particle

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5
Q

Name 3 structures that can be found in viruses

A

1) Nucleocapsid core
2) Capsid
3) Envelope (some viruses)

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6
Q

Define in terms of viruses:
1) Nucleocapsid core
2) Capsid

A

1) Viral nucleic acid (DNA or RNA) that is held within a protein coat called a capsid
2) The protein coat that surrounds the viral nucleic acid genome

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7
Q

Define in terms of viruses:
1) Enveloped virus
2) Naked virus

A

1) Enveloped: The viral nucleocapsid is surrounded by an additional layer that can be very complex containing carbohydrates, lipids, and additional protein.
2) Naked virus: Viruses lacking an envelope

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8
Q

The three types of viral capsid architecture are based upon what?

A

The symmetry of the capsid/ nucleocapsid

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9
Q

Name and describe the three types of viral capsid architecture

A

1) Icosahedral: usually naked viruses, a few are enveloped
2) Helical: can be naked or enveloped
3) Complex: A complex structure that is neither of the above

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10
Q

What are the 3 functions of the capsid?

A

1) Packages the genome/provides structural support
2) Protects the genome from nucleases (in serum) and adverse environmental conditions
3) Participates in attachment and entry of host cells

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11
Q

1) Icosahedral capsids are made up of what?
2) What is the smallest repeating structural unit visible by electron microscopy that makes up the icosahedral nucleocapsid?

A

1) The capsids are constructed from ring or knob-shaped units called capsomers
2) A capsomer

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12
Q

1) In terms of viruses, what are capsomers made up on?
2) What are capsomers made of?

A

1) Capsomers are made up on one or more viral structure (or capsid) proteins
2) Each capsomer is usually made of five or six protomers

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13
Q

1) What groups of viruses have envelopes?
2) What do virus envelopes usually arise from?
3) What usually codes for viral envelope proteins?

A

1) Many animal viruses, some plant viruses, and at least one bacterial virus have an envelope.
2) Virus envelopes usually arise from host cell nuclear or plasma membranes;
their lipids and carbohydrates are normal host constituents
3) Viral envelope proteins are coded for by virus genes

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14
Q

1) What are projected proteins in viruses and what are they called?
2) What do many projected proteins act as? What do the rest do?

A

1) Viral envelope proteins may project from the envelope surface
Projected proteins are called spikes. 2) Many act as VAPs: Viral Attachment Proteins. Some are enzymes (e.g. neuraminidase, polymerases).

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15
Q

1) Name the 2 protein spikes found on the surface of the influenza virion
2) How many pieces of RNA or DNA does it have?
3) What species can be infected by influenza, and what changes about influenza when it changes species?

A

1) Hemagglutinin (HA) spike and neuraminidase spike
2) Very few genes; only 8 pieces of RNA that encode for all the proteins it needs.
3) Goes through pigs, birds, and humans.
Temperature changes and amino acid changes occur as the virus makes its way through different species.

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16
Q

1) What can the viral factors of influenza do?
2) What are the host factors (vulnerability factors) for influenza infection?

A

1) Has viral factors (based on its genotype) that can block interferons from helping the immune system, aid in replication, and HA spike determines receptor binding.
2) Host factors: Underlying health issues, elderly age, etc.

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17
Q

List the component, properties, and consequences (5) of the naked capsid viral structure

A

1) Component: Protein
2) Properties: Is environmentally stable to temperature, acid, proteases, detergents, and drying; is released from cells by lysis
3) Consequences:
1) Can be spread easily
2) Can dry out and still retain infectivity
3) Can survive the adverse conditions of the gut
4) Can be resistant to detergents and poor sewage treatment
5) Antibody many be sufficient for immunoprotection

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18
Q

List the components (3), properties, and consequences (5) of the enveloped capsid viral structure

A

1) Components:
a) Membrane
b) Lipids
c) Proteins and glycoproteins
2) Properties: Is environmentally labile and is disrupted by acid, detergents, drying, and heat; modifies cell membrane during replication and is released by budding and cell lysis.
3) Consequences:
a) Must stay wet
b) Cannot survive the gastrointestinal tract
c) Spreads in large droplets, secretions, organ transplants and blood transfusions
d) Does not need to kill the cell to spread
e) May need antibody and cell-mediated immune response for protection and control

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19
Q

Are naked or enveloped viruses more resistant to drying out?

A

Naked viruses

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20
Q

1) What two types of genome can viruses contain?
2) What are the two types of DNA or RNA genome a virus can have?

A

1) Viruses can contain a DNA or RNA genome
2) The DNA or RNA genome can be single (ss) or double stranded (ds)

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21
Q

1) How does the Baltimore classification system classify viruses? (what is it based on?)
2) What two things are true of all viruses?

A

1) Sorts viruses based on their genome
2) a) Eventually need to get to mRNA to create proteins.
b) Have the ability to replicate their genome

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22
Q

List the 5 generalized steps of the viral life cycle

A

1) Adsorption: Host cell recognition and attachment of virus
2) Entry: of viral nucleocapsid or nucleic acid
3) Synthesis: of viral proteins and nucleic acids (eclipse phase)
4) Self-assembly: of virions
5) Release: of progeny virions

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23
Q

Each cell can produce _______ particles (viruses) but only ______ of those are infectious due to the high mutation rate because of self-assembly.

A

100,000; 1-10%

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24
Q

Describe the ‘attachment’ phase of the viral life cycle:
1) What is it mediated by?
2) What is usually its cell surface receptor?
3) What is it the determinant of?
4) What has the ability to block this interaction?
5) What do cell surface receptors normally do when not attached to a virus?

A

1) Mediated by viral envelope/capsid protein (called a viral attachment protein or VAP) that binds to a target cell receptor molecule.
2) Cell surface receptor is usually a specific cell surface glycoprotein or a carbohydrate moiety attached to a lipid.
3) Determinant of cell/tissue tropism (which cells it can infect).
4) Interaction can be blocked by a neutralizing antibody; the attachment step is major target for the immune system.
5) Cell surface viral receptors have important functions in normal host cellular metabolism.

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25
Q

Give an example of attachment using influenza

A

Influenza’s hemaglutinin attachment protein recognizes target vertebrate cells and initiates fusion between host and viral membranes, determines how well it can infect.

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26
Q

Describe the ‘entry’ phase of the viral ‘life’ cycle in enveloped viruses:
1) What two ways can they use to enter the host cell?
2) What mediates their fusion?
3) When is the viral envelope removed?
4) What is the fusion process dependent on?

A

1) Enveloped viruses can enter by fusion of viral envelope with a cellular membrane or by endocytosis
2) Fusion is mediated by a viral “fusion” protein
3) Viral envelope is removed when fusion occurs and the viral nucleocapsid is ‘ejected’ into the host cell’s cytoplasm
4) Fusion process is pH dependent; cell surface at neutral pH vs fusion occurs in an endosome at an acidic pH

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27
Q

Describe the ‘entry’ phase of the viral ‘life’ cycle in naked viruses:
1) How do they enter the host cell?
2) What is released after entry? What is extruded?

A

1) Naked viruses enter by receptor mediated endocytosis
2) After entry, the viral nucleocapsid is released into host cell cytoplasm and uncoated, or the viral genome is extruded into host cell cytoplasm through the endosome or plasma membrane (viropexis)

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28
Q

Describe the ‘uncoating’ phase of the viral ‘life’ cycle:
1) What is stripped away from the viral nucleic acid?
2) Where does the viral genome travel after it’s uncoated?

A

1) Nucleocapsid proteins are partially or completely stripped away from the viral nucleic acid
2) Uncoated viral genome travels to site of genome replication

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29
Q

1) Where do DNA viruses usually replicate?
2) Where do RNA viruses usually replicate?

A

1) DNA viruses usually replicate in the nucleus of a host cell
2) RNA viruses usually replicate in the cytoplasm of a host cell

30
Q

1) Define the ‘replication’ phase of the viral ‘life’ cycle
2) What 3 things occur during this phase?

A

1) Defined as the production of viral components
2)
a.Genome replication
b. Production of viral mRNAs
c. Production of viral proteins

31
Q

What two things are produced during the ‘replication’ phase of the viral ‘life’ cycle?

A

1) Viral mRNAs
2) Viral proteins

32
Q

1) Define the ‘assembly’ phase of the viral ‘life’ cycle
2) Where are DNA viruses usually assembled?
3) Where are RNA viruses usually assembled?
4) What directs the genome to new capsids?
5) How do the viral proteins assemble?

A

1) The assembly and maturation of new virions
2) DNA viruses are usually assembled in the host cell nucleus
3) RNA viruses are usually assembled in the host cell cytoplasm
4) The viral genome contains “packaging signals” that direct it to new capsids
5) The viral proteins “spontaneously” assemble at the correct site in the cell (along with the nucleic acid genome)

33
Q

1) Define the ‘release’ phase of the viral ‘life’ cycle
2) How are enveloped viruses released? When do they pick up their membrane?
3) How are non-enveloped viruses usually released?

A

1) The release of new virions
2) Enveloped viruses are released by budding through the appropriate cell membrane
Viruses pick up their membrane during the process of budding
3) Non-enveloped viruses are usually released by lysis of the host cell

34
Q

1) Where are DNA viruses replicated? Where are they assembled?
2) Where are RNA viruses replicated? Where are they assembled?

A

1) DNA viruses are usually both replicated and assembled in the host nucleus
2) RNA viruses are usually both replicated and assembled in the host cytoplasm

35
Q

Describe replication in the Herpes Simplex Virus Type I

A

Rolling circle replication creates a byproduct called concentric DNA, which is where multiple copies of that DNA are readily available in the nucleus

36
Q

There are 3 possible outcomes of a viral infection of a cell (viral pathogenesis); what are they?

A

1) Abortive infection: Failed infection; virus was unsuccessful.
2) Lytic infection: Ends in cell death
3) Persistent infection: Infection without cell death

36
Q

What are the 3 types of persistent infections? Describe them

A

1) Senescence: Viruses are produced and the cell stops dividing but is still alive. A type of persistent infection.
2) Latent: Virus production may stop and start, has no effect on the cell. A type of persistent infection.
3) Transforming (of a host cell; the integration of viral DNA in the cell): DNA viruses are not produced, RNA viruses are produced. Causes immortalization (cancer). A type of persistent infection.

37
Q

What type of viral infection results in a cell becoming cancerous?

A

Transforming infections (a type of persistent infection)

38
Q

Define cytocidal infection and cytopathic effects

A

1) Cytocidal infection: an infection that results in cell death
2) Cytopathic effects: microscopic or macroscopic degenerative changes or abnormalities in host cells and tissues

39
Q

List the 8 possible mechanisms for host cell damage (by viral pathogens)

A

1) Inhibition of host DNA, RNA, and protein synthesis
2) Damage of cell endosomes; results in release of hydrolytic enzymes
3) Alteration of plasma membranes by insertion of viral proteins; infected cells are attacked by host immune system
4) High concentrentration of viral proteins can have direct toxic effect on cells and organisms
5) Formation of large intracellular structures called inclusion bodies (often composed of subunits of viral proteins or host cell components) which disrupt cell structure
6) Chromosomal disruptions
7) Host cell is not destroyed, but is transformed into a malignant cell
8) Cell fusion: expression of viral envelope/ fusion proteins on the surface of an infected cell. Can cause it to fuse with nearby, uninfected cells. Fused cells usually die and are called syncytia or multinucleated giant cells.

40
Q

What are the 8 steps of the viral disease process (viral pathogenesis)?

A

1) Transmission
2) Entry into host
3) Primary viral replication
4) Viral local/ systemic spread
5) Secondary viral replication/ cell tropism
6) Cell damage/ disease production
7) Shedding of virus
8) Host death/ recovery

41
Q

What are the 3 primary modes of transmission of viruses?

A

1) Direct transmission (horizontal and vertical transmission)
2) Animal to human transmission
3) Transmission by arthropod vector

42
Q

Define horizontal and vertical transmission of viruses

A

1) Horizontal transmission: from person to person
2) Vertical transmission: from mother to child (perinatal and natal)

43
Q

What are the most common ways viruses are transmitted?

A

Inhalation and inoculation of virus into mucosa on contaminated hands/ objects are the most common ways viruses are transmitted

44
Q

1) Where do viruses enter their host cell?
2) What are the two main barriers for entry of viruses?

A

1) Portal of entry
2) Mechanical/ physical barriers and adaptive barriers (the immune response)

45
Q

Differentiate between:
1) Primary replication
2) Primary replication + secondary infection

A

1)The production of disease at a virus’s portal of entry (short incubation times)
2) Cells at the portal are infected, virions are produced, and systemically spread to a second site. Requires longer incubation times.

46
Q

What mechanisms of spread can be used by viruses in secondary infection? (3)

A

1) Bloodstream (viremia)
2) Lymphatics
3) Neuronal spread: uses neurons as conduits.

47
Q

What are the 3 types of tissue tropism?

A

Specific tissue, cell tropism, specific cell type

48
Q

What two barriers in the human body are highly effective in keeping viruses out?

A

1) Blood-brain barrier
2) Placental barrier

49
Q

Define direct and indirect tissue damage

A

1) Direct tissue damage: damage that occurs by replicating in, and killing or transforming host cells
2) Indirect tissue damage: the immune response to viral infection causes cell/ tissue damage (symptoms)

50
Q

1) Where are viruses typically shed?
2) When are those infected with a virus most contagious?

A

1) Usually the virus is shed from the same body surfaces at which it enters
2) During active shedding

51
Q

What influences whether or not a host lives or dies from a viral infection?

A

Just like with bacteria, all of the following play a role:
1) Strains
2) Type of virus
3) Host genetics and immune system

52
Q

Differentiate between apparent and inapparent viral infections. Which is more common?

A

1) Inapparent infections: subclinical or asymptomatic infection
a) Virus replicates in the host, but no clinical symptoms develop
Most common type of infection
2) Apparent infection: symptomatic infections; can either be acute or persistent

53
Q

1) What are the two types of apparent viral infection?
2) What are the two types of persistent viral infection?

A

1) Acute and persistent
2) Chronic and latent

54
Q

Differentiate between acute and persistent viral infections

A

1) Acute infections:
Overall rapid onset and last for a short period of time (days to weeks; ex: influenza)
2. Persistent infections: Lasting many years; can be chronic or latent

55
Q

Differentiate between chronic and latent viral infections. Give examples of each.

A

1) Chronic virus infections; virus is almost always detectable, but clinical symptoms may be either mild or absent for long periods
a) Examples: Hepatitis B virus and HIV
2) Latent virus infections; virus stops reproducing and remains dormant for a period before activating again.
During latency there are no symptoms (viruses are hidden or less potent)
a) Examples: Herpes simplex virus, Varicella-zoster virus, Epstein-Barr virus

56
Q

What causes latency in viral infections? (4 steps)

A

1) Viral genome was incorporated into the chromosome (provirus or phage).
2) Virus becomes less antigenic (less susceptible to immune attack).
3) The virus hides in an area that can’t be reached by the immune system (ex: nervous system).
4) Then the virus mutates to the less virulent form, which slows production.

57
Q

List the 8 different ways viruses evade host antiviral immune defenses

A

1) Overwhelming the host quickly
2) Production of large quantities of virus and/or viral antigens
3) Shedding of virus from site of primary infection
4) Infection of cells of the immune system
5) Production of “Anti-Immune” Substances (Molecular Bombs)
6) By replication in immune privileged sites (ex: eye or CNS)
7) Establishment of latent infection.
8) By undergoing antigenic variation (alteration of viral antigens); the emergence of new variants.

58
Q

Overwhelming the host quickly is characteristic of what viruses?

A

Characteristic of acutely lethal viruses (e.g. Ebola)

59
Q

1) Why does producing large quantities of the virus or viral antigens work against the host immune system?
2) Why does shedding the virus from the primary site of infection work against the host immune system?

A

1) The immune system can’t keep up
2) The immune response has not developed

60
Q

What are the 4 types of anti-immune substances (molecular bombs) that can be made by viruses?

A
  1. Virokines: virally encoded cytokine analogues
  2. Viroreceptors: virally encoded cytokine receptor analogues
  3. Inhibitors of MHC class I antigen presentation
  4. Inhibitors of the Interferon response
61
Q

Differentiate between virokines and viroreceptors

A
  1. Virokines: virally encoded cytokine analogues
  2. Viroreceptors: virally encoded cytokine receptor analogues
62
Q

What are the two types of viral antigenic variaiton? Describe them.

A

1) Antigenic drift: accumulation of point mutation in viral gene(s) changes their antigenicity.
2) Antigenic shift: exchange of genome segments between two different serotypes of virus infecting the same cells results in production of viral progeny which contain genes/antigens from both parental virus strains. Can result in the emergence of new pathogens.

63
Q

Differentiate between antigenic drift and antigenic shift

A

1) Antigenic drift: accumulation of point mutation in viral gene(s) changes their antigenicity.
2) Antigenic shift: exchange of genome segments between two different serotypes of virus infecting the same cells results in production of viral progeny which contain genes/antigens from both parental virus strains. Can result in the emergence of new pathogens.

64
Q

What mediates the innate immune response to viral infection?

A

Interferons

65
Q

Describe how DAIs (double-stranded RNA-activated inhibitor) work (3 steps)

A

1) A part of our innate immune system that’s normally inactive, until it sees a virus with double-stranded RNA.
2 )Then DAI phosphorylates and becomes active, and recruits initiation factor II and activates it.
3) Then it deactivates initiation factor II by phosphorylating it, which slows down synthesis of viral proteins and gives the cell more time to kill the virus (or kill itself).

66
Q

How do viruses combat DAIs of the innate immune system?

A

Some viruses have extra genetic material called ‘small RNAs’ that they bring with them in their capsules; these small RNAs have the ability to bind to and lock DAI in an inactive state (so it can’t phosphorylate to activate)

67
Q

List the 3 primary bacterial evasion strategies and how viruses respond to them

A

1) Receptor issues: The bacteria changes the receptor to prevent the virus from binding. The virus in turn learns how to bind to the new receptor.
2) Running interference: Bacteria put tons of sugars on their surface, preventing the virus from reaching the host cell surface. Viruses then begin to carry enzymes that break down sugars.
3) New coat: The bacteria modify their sugars and create variations in them so the viruses can no longer interact with the sugar coat.

68
Q

How do you cultivate viruses?

A

1) Create a lawn of bacteria on a plate
2) Add virus to the bacterial lawn
3) The virus begins to form plaques and lyse bacterial cells

69
Q

1) Define viroids.
2) How do viroids replicate?
3) What do viroids infect?
4) What are the two families of viroids?

A

1) Viroids are unencapsulated nucleic acids that consist of only RNA
2) Despite their small size and limited genetic info, they replicate autonomously (rolling circle replication)
3) Cause diseases in higher plants
4) One replicates in nucleus, other in chloroplasts

70
Q

1) How do viroids move?
2) How old are viroids?
3) How do viroids act as pathogens?

A

1) Move intracellularly, accessing neighboring cells through plasmodesmata
2) They’re ‘molecular fossils’ and predate the current world of DNA and protein (supports RNA World Hypothesis).
3) They don’t encode proteins, they act through a method called RNA silencing (binds and stops things from happening in host cell)

71
Q

1) Define prions
2) What are the two forms prions exist in?
3) What happens if the two prion types interact?
4) How do prions act as pathogens?

A

1) Proteinaceous infectious particles that cause neurodegenerative disease
2) Abnormally folded form and normal cellular form
3) Interaction between the two prion types usually causes the normal form to turn into the abnormal form.
4) Crosslinking of normal protein > triggers apoptosis > neuron loss