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Virology > Lecture 1 and 2 - Introduction > Flashcards

Lecture 1 and 2 - Introduction Flashcards

1
Q

What does virus mean in latin?

A

Slimy liquid or poison

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2
Q

What is a virus?

A

Virus: submicroscopic filterable (< 0.2 µ) infectious agent multiply only in living cells

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3
Q

What kind of parasites are viruses?

A

Viruses are obligate parasites that are metabolically inert when they are outside their hosts.

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4
Q

What does a virus rely on?

A

Viruses rely, to varying extents, on the metabolic processes of their hosts to reproduce themselves.

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5
Q

Do viruses have cellular organelles?

A

Viruses: Do not have cellular organelles (mitochondria, chloroplasts, Golgi, and endoplasmic reticulum or ribosomes.

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6
Q

What do viruses have in terms of biology?

A

Viruses: have nucleic acids in the form of DNA or RNA, never both except Retroviruses

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7
Q

What is a virion?

A

Virions are the mature extracellular infectious viral particle produced by the infected cells under the control of the genetic materials of the virus.

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8
Q

What is a viroid?

A

Viroid: an infectious entity affecting plants, smaller than a virus and consisting only of nucleic acid without a protein coat.

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9
Q

What is a satellite or defective virus?

A

Satellite or Defective Viruses: Viruses require a second virus (helper virus) for replication
Ex: Hepatitis delta virus requires the presence of HBV to complete its replication cycle.

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10
Q

What is the living criteria of viruses?

A
  • Control and divert cellular function for their own purposes.
  • Can multiply: viral genome, genetic code, new viral components are synthesized and assembled within the infected host cell.
  • Viruses may undergo mutation.
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11
Q

What is the nonliving criteria of viruses?

A

Viruses are not able to reproduce on their own
• Viruses must infect other cells in order to perpetuate their life cycle
• Viruses can be crystallized but no other cells can be crystallized
• Viruses do not have energy generating (ATP) machinery
• Viruses do not have metabolic machinery
• Viruses do not have the necessary machinery for generating nucleic acid or protein
• Viruses do not contain cytoplasm or any cellular organelles
• Viruses may contain membranous envelope derived from the infected host cells during viral exit

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12
Q

What are the reasons for the non life viral theory?

A

Viruses are considered to be non-living because:

  • Are not cells
  • Do not grow or respond to their surroundings
  • Can not make food, take in food, or produce wastes
  • They do not respond to stimuli
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13
Q

What are the reasons for the life viral theory?

A

have only two fundamental characteristics of the living system

  1. the presence of nucleic acid as genetic material
  2. the ability to replicate and produce their own copies.
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14
Q

What is the conclusion found between the living and nonliving viral theories?

A

Viruses can only multiply in another cell. • Conclusion: viruses are nonliving outside the cells but live inside the cell

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15
Q

What are some characteristics of viruses that they do not share with other microorganisms?

A

Viruses do not:
- isolate/ propagate on synthetic media
- reproduce with binary fission
- contain both DNA and RNA
- have presence of energy machinery
- have metabolism
- have a size > 300 nm
- cannot be detected by light microscope ( Most viruses can only be seen under EM except in cases of giant viruses as Mimivirus can be seen by light microscope)
- have a cell wall.
Viruses do have IFNs sensitivity.

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16
Q

What determines the mutation rate of viruses?

A

Mutation rates are primarily determined by the type of viral nucleic acids
• RNA polymerase fidelity and transcriptional proofreading (DNA/RNA) polymerases

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17
Q

What is the criteria of classification of viral order ?

A

Group of virus families sharing certain common characters

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18
Q

What is criteria of classification of viral family?

A

A group of genera sharing certain common characters with each others

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19
Q

What is criteria of classification of viral sub-family?

A
  • A group of genera sharing certain common characters
  • Used only when it is needed to solve a complex hierarchical problem
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20
Q

What is criteria of classification of a viral genus?

A

A group of related species that share some significant properties Usually only differ in host range and virulence

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21
Q

What is criteria of classification of a viral species?

A

Consist of as few words must not consist only of a host name

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22
Q

What are the physical properties used as criteria in viral classification?

A

Physical properties of viruses

  • Type of viral NA
  • The strandedness of the NA (ss or ds)
  • Viral size
  • Symmetry of viruses
  • Total number of Capsomeres per virus
  • Presence or absence of the viral envelope
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23
Q

What are the chemical properties used as criteria in viral classification?

A

II. Chemical properties of the viruses

  • Heat sensitivity
  • pH sensitivity
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24
Q

What are the biological properties used as criteria in viral classification?

A

III. Biological properties of viruses

  • Cytopathology (CP)
  • Site of replication (IC or IN)
  • Inclusion bodies
  • Hemagglutination property
  • Antigenic properties
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25
Q

Parts of a virus: What is the inner core? What is inside this region?

A

Inner core: (Nucleic acids, NA) -Always occupy the central region of the virus

  • Usually coiled to packed into a small space
  • May be double-stranded (ds) or single-stranded (ss)
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26
Q

What are the double stranded viruses? single stranded?

A
  • ds: most of the DNA viruses; exception; Parvovirdae and Circovirdae (ss)
  • ss: most RNA viruses; exception; Reoviridae and Birnavirdae (ds)
  • Sometimes segmented: Influenza viruses, Reovirues, and Birnaviruses
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27
Q

Parts of a virus: What is the outer membrane? What is its role/ what does it contain?

A

Outer membrane: (Viral capsids)

  • Surrounds the NA
  • composed of repeated subunits called capsomeres
28
Q

Parts of a virus: What is the additional outer membrane? What is its role/ what does it contain?

A

-Lipo-protein layer acquired from the cell membrane of the infected cells
-Usually covered with some projections called peplomers
Examples of enveloped viruses: Coronaviridae, Influenza viruses

29
Q

What do you call non enveloped viruses?

A

naked viruses.

30
Q

What are the 3 types of symmetry classifications of viruses?

A
  • Hellical
  • Icosahedral
  • Complex
31
Q

What is the capsid? What are capsomeres?

A

Capsid: the protein shell surrounding the nucleic acid
Capsomeres-: the structural subunits of the capsid

32
Q

What is the function of viral capsids?

A
  • Protects viral genome
  • Serves as an attachment protein (only in the case of naked non enveloped viruses) and bind the virus to susceptible host cells thereby promotes virus entry into cells
  • Stimulate the immune response to produce antibodies against the virus
  • Facilitates the assembly and packaging of the viral genetic materials
33
Q

What does it mean for a virus to have helical symmetry?

A
  • Capsomers arranged around the NA in a helical fashion
  • Capsomers attached directly to the helix of NA
  • Most of the helical viruses are enveloped, and all are RNA viruses
  • Examples: TMV
34
Q

What does it mean for a virus to have icosahedral or cubic symmetry?

A
  • Capsomeres arranged around the NA in a icosahedral fashion
  • Capsomers form a regular icosahedron composed of 20 equilateral triangular facets
  • Two types: pentagons or hexagons at vertices
  • Examples: Adenovirus, Picornavirus, Papovavirus, herpes
35
Q

What does it mean for a virus to have complex symmetry?

A

-Mixture of asymmetric NA in an icosahedral fashion in a helical fashion and symmetric structures
Poxvirus has a unique complex structure
- Examples: Poxviruses and Bacteriophages

36
Q

What kind of virus is this?

A

Naked icosahedral

37
Q

What kind of virus is this?

A

Naked helical

38
Q

What kind of virus is this?

A

Enveloped Hellical

39
Q

What kind of virus is this?

A

Enveloped helical

40
Q

What is a viral envelope?

A

Envelope: the outer shell surrounding the viral nucleocapsid in case of enveloped
viruses

41
Q

What is the structure of a viral envelope?

A

• Structure of the viral envelope:

  • Lipid bilayer derived from the host cell membrane during the virus exit from the cell
  • Glycoproteins
42
Q

What is the function of the viral envelope?

A

Functions of viral envelope:

  • Protects viral nucleocapsid - Mediates viral attachment and entry into the host cells
  • Viral attachment proteins as
  • HA in case of influenza viruses
  • Spike in case of Coronaviruses
  • Mediates viral entry into the host cells
  • Fusion protein as in case of the New Castle Diseases virus
43
Q

What are enveloped viruses sensitive to?

A

Clinical applications: enveloped viruses are sensitive to lipid solvents and
common disinfectants

44
Q

Can a virus have more than one type of peplomers? Can they have more than one function?

A

yes

yes

45
Q

What are the 2 functions of HN peplomers in paramyxoviruses?

A

1- Hemagglutination of the RBCs of some animals species
2- Neuraminidase causes elution of the agglutinated RBCs and facilitates the virus entry

46
Q

What is the function of HA peplomers in influenza viruses?

A

Hemagglutinates some RBCs

47
Q

What are other functions of peplomers? Do they have some antigenic properties?

A
  • Some viral peplomers induce fusion of various cells together to form syncytium
  • Viral peplomers have some antigenic properties
48
Q

What is a +Ve sense genome?

A

Strand of viral RNA that can immediately serve as a template mRNA for protein synthesis during the process of translation.

49
Q

What is a -Ve sense genome?

A

Strand of viral RNA that must first be converted into complementary positive sense strands before creating protiens.

50
Q

What is an ambisense viral genome?

A

An RNA viral genome that is part of positive and in part of negative polarity.

Both nucleic acid strands encode protiens.

51
Q

What is the function of viral genetic materials?

A
  • Carries the genetic blueprint for the progeny production
  • Codes for the synthesis of viral enzymes required for viral replication.
  • Codes for the synthesis of viral structural proteins required for viral assembly
52
Q

Do all DNA viruses have Ds genomes?

A

• All DNA viruses have ds genomes except Parvoviridae and circoviridae

53
Q

Do all RNA viruses have SS genomes?

A

All RNA viruses have SS genomes except Reoviridae and Birnaviridae

54
Q

What is the optimal pH for growth and multiplication of viruses?

A

Neutral

55
Q

What happens to viruses in extremely acidic/ extremely alkiline ph?

A

media are deleterious to most viruses

56
Q

Can any virus survive a pH of 10?

A

pH 10: is detrimental to most viruses
- Exception: African swine fever virus (ASFV) – stable at pH 4-13

57
Q

What are the strategies of viral inactivation?

A
  • Denaturing of viral protiens by:
  • Phenol derivatives (Lysol) -Ammonium compounds (Roccal) -Sodium hypochlorite (Clorox)/oxidizing agent -Hydrogen peroxide/oxidizing agent
  • Iodophors (mixture of iodine and surfactants)- oxidizing agent
  • Inactivation of viral protiens
  • First: soaking the viral solution in (1 N NaOH)
  • Second: autoclaving for 1.5 hrs

• Denaturing both viral nucleic acids and proteins

  • Formaldehyde (1-5%), - Glutaraldehyde (2%)
  • Ethylene oxide (fumigation) – extremely toxic (must be used in a sealed chamber).
  • UV light: cross links the pyrimidine bases (C & T/U)

• Dissociation of viral envelopes:
- 70 % alcohol mixed with water result in lipid disruption and denaturing of proteins

58
Q

What is some beneficial roles of viruses?

A

Baculoviruses: modified by genetic engineering to express some other viral proteins for vaccine purposes as well as development of some novel diagnostic assays

  • Poxviruses and Adenoviruses used as viral vectors
  • Lentiviruses: modified to insert some foreign genes of interest into cells for research purposes and gene therapy
  • Bacteriophages: used in the control of some bacterial infections
59
Q

What are bacteriophages?

A
  • Viruses specifically infect bacteria
  • They are obligate intracellular parasites
  • Infect various bacterial species, but most extensively investigated phages infect enteric bacteria, E. coli, and Salmonella
  • Phages can be DNA or RNA and either double or single-stranded.
60
Q

What is the structure of a bacteriophage?

A

• They have a capsid (head), a sheath, and tail fibers, which are contractile. The
capsid has the DNA. The tail fibers attach to the bacterial cell surface and
inject the DNA into the cell.

61
Q

How do bacteriophages replicate?

A

The Lytic Cycle: the host bacterial cell is lysed (lytic phages)
The Lysogenic Cycle: host bacterial cell remains intact and alive
the life cycle results in a stable genetic relationship with the host. The phages are called temperate phages

62
Q

What is phage theory?

A

Phage therapy is the therapeutic use of lytic bacteriophages to treat bacterial infections

63
Q

How specific are phages? How is this adventagous?

A

Most phages are specific to one species of bacteria, and many are only able to lyse
specific strains within a species.

• The limited host range can be advantageous, in principle, as phage therapy results in less harm to the normal body flora and ecology than commonly used antibiotics

64
Q

How are lytic phages similar to antibiotics?

A

• Lytic phages are similar to antibiotics in that they have remarkable antibacterial activity • Therapeutic phages have some advantages over antibiotics

phages have been reported to be more effective than antibiotics in treating certain infections in humans and experimentally infected animals.

65
Q

When has lytic phages been more effective than antibiotics?

A
  • Staph aureus phages treating patients with purulent disease of the lungs
  • phages used to reduce e coli on hide sufaces prior to slaughter
66
Q

True or False: Phages are preferable to antibiotics, because bacteria cannot develop a resistance to phages.

A

FALSE

Bacteria can also develop resistance to phages

Virology (9 decks)

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