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LSCI 230: Microbiology > Taxonomy of Viruses > Flashcards

Taxonomy of Viruses Flashcards

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1
Q

General characteristics of viruses

Ecological interactions? Hosts? Consists of?

A
  • Obligate intracellular parasites
  • Host cells include all groups of organisms
  • Piece of nucleic acid enclosed within a protein coat
  • 1 type of nucleic acid found in the virion of a given virus
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2
Q

Virions

A
  • Outside of the host
  • inert infectious particles
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3
Q

Capsid

A

Protein coat around the nucleic acid

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4
Q

Nucleocapsid

A

Nucleic acid + protein coat

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5
Q

Capsomeres

A

Protein subunit that makes up the capsid

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6
Q

Envelope

A

Lipid-containing layer with embedded proteins
* Proteins in the envelope are virus specific

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7
Q

Shapes of Virions

A
  • Helical virus: Typical of many plant viruses
  • Polyhedral virus: most common is icosahedron
  • Complex virus: Composed of several parts
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8
Q

Viroids

A
  • Closed circles of single-stranded RNA containing 240-380 nucleotides
  • Replication is dependent on host machinery
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9
Q

Prions

A
  • Consists solely of 1 protein
  • Commonly found in neurons
  • Induces misfolding of normal prion proteins who’s accumulation kills cells
  • Cause of many neurological degenerative disorders
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10
Q

Taxonomy

Virus

A
  • Grouped into families (end in “-viridae”)
  • Given a genus name (end in “-virus”)
  • Given a species name (usually English)
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11
Q

Classificationof viruses

A

Based on characteristics:
* Nature of the host
* Type of disease caused
* Life cycle
* Naked or enveloped
* Type of nucleic acids and strandedness

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12
Q

Baltimore classification scheme

A

Classification is based on the type of genome

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13
Q

Pathway of viruses

A
  • Absorption
  • Penetration
  • Uncoating
  • Replication
  • Maturation
  • Release
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14
Q

Absorption

Life cycle

A

Attachment of the virus to
specific receptors on the surface of the cell

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15
Q

Penetration

Life cycle

A

Virus genome enters the cell
* The complete virion may enter the cell
* In enveloped viruses: Envelope may be left at the cell surface
* In naked viruses: Capsid may be left at the surface

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16
Q

Uncoating

Life cycle

A

Removal of the envelope and\or
the capsid by host enzymes

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17
Q

Replication

A

Replication of the nucleic acid,
transcription and protein synthesis

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18
Q

Maturation

A

Assembly of virus components, nucleic acid, nucleocapsid and accessory proteins to form new virions

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19
Q

Release

A

Mature virions exit the host cell by means of budding or by causing lysis of the cell.

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20
Q

Latent period

A

Eclipse (replication) + maturaiton
* Eclipse (replication): time necessary for the host cells to replicate the viral genome and to synthesize the viral components
* Maturation: time needed for the different components to be assembled

21
Q

Rise period (release)

A

Virions are detected outside the cell
* Lysis: virus-encoded proteins damage the CM
* Budding

22
Q

Burst size

A

Number of virions released

23
Q

Bacteriophages

A
  • Viruses of bacteria
  • Most phages contain linear dsDNA genomes
  • Most are naked, but some possess lipid envelopes
24
Q

Bacteriophage Types

A
  • Virulent phages
  • Temperate phages
25
Q

Lytic pathway

A

Infection of host cells always leads to replication resulting in host cell lysis
* Virulent and temperate phages

26
Q

Lysogenic pathway

A

Genome becomes incorporated into the bacterial host genome
* Temperate phages

27
Q

Virulent Phage: T4

A
  • T4 attaches to the core region of LPS by the tail fibers
  • Tail lysozymes digest the peptidoglycan layer, forming a small pore
  • Phage DNA is injected into the cytoplasm of the host cell
  • Replication of T4 dsDNA
  • T4 lysosome production leads to cell lysis
28
Q

Temperate Phage: Lambda

A
  • Genome = linear dsDNA with cohesive ends that join to form circular molecule
  • Genome integrated in the bacterial chromosome at the attƛ site (homologous to the att site in the phage)
  • Infection by temperate phages results in a prolonged, latent state of infection
  • Sometimes, the prophage can exit the chromosome and continue along the lytic pathway
29
Q

Prophage

A

phage genome within the
host cell chromosome

30
Q

Lysogen

A

bacterium that contains a
prophage

31
Q

Location of replication in animals viruses

A
  • DNA genome: in the nucleus
  • RNA genome: in the cytoplasm
32
Q

Animals viruses types

A

DNA genome

RNA genome:
* plus-strand RNA
* minus strand RNA
* dsRNA
* Retrovirus RNA

33
Q

DNA genome

A
  • Fusion of cell CM with virus envelope
  • Nucleocapsid transported to nucleus where viral DNA is uncoated
  • Host apparatus synthetizes immediate early proteins, delayed early proteins, & late proteins
  • Assembly occurs in the nucleus
  • envelope is added via a budding process through the inner membrane of the nucleus
  • Ex: Herpes virus
34
Q

RNA genome: + strand RNA

A

The genome can be translated directly
* Ex: Poliovirus, Hepatitis A virus

35
Q

RNA genome: - strand RNA

A

The minus-strand is first transcribed into a plus-
strand RNA by an RNA-dependent RNA polymerase carried inside the virions
* Ex: Measles, Rabies, Influenza

36
Q

RNA genome: dsRNA

A
  • A plus-strand RNA must be synthetized by a viral-encoded RNA-dependent RNA polymerase using the minus strand as the template.
  • The plus-strand is then translated into proteins and is used as a template to synthesize a minus strand to yield dsRNA genomes
  • Ex: Rotavirus
37
Q

RNA genome: Retrovirus

A
  • The virion carries two identical copies of the genome (plus-strand ssRNA), reverse transcriptase, integrase and proteases.
  • The reverse transcriptase reverse transcribes the RNA genome into DNA
  • The DNA genome travels to the nucleus and is integrated into the host DNA
  • Ex: HIV
38
Q

Long terminal repeats (LTR)

A

Contain promoters for transcription and participate in the integration process of viral DNA

39
Q

Provirus

A
  • Integrated viral DNA
  • Cannot excise from the host genome
40
Q

Consequences of viral infections in animal cells

A
  • Cell fusion
  • Oncogenic viruses
41
Q

Cell fusion

A

Enveloped viruses that fuse with the host cell cytoplasmic membrane
* results in hybrid cells that have chromosomal aberrations

42
Q

Transformation

A

Conversion of a normal cell into a tumor cell

43
Q

Oncogenic Viruses

A

Viral infection is implicated in transformation
* Both DNA and RNA viruses are know to cause tumours

44
Q

Mechanisms of oncogenic viruses

A
  • Transduction
  • Insertion of a strong promoter
  • Inactivation of a tumor suppressor gene.
  • Expression of viral protein that induces transformation
45
Q

Expression of viral protein that induces transformation

A
  • DNA virus
  • The viral protein does not have a cell counterpart
  • Integration of the viral genome into the host genome may occur or the viral genome may persist in the cell as an extrachromosomal episome
  • Ex: HPV
46
Q

Nonpermissive host

A

A host in which a virus cannot complete its infection cycle
* The infected undergoes uncontrolled replication (tranformation)
* Because the virus cannot complete its replication, the cells will never die

47
Q

Nucleoside analogs

A

Block reverse transcriptase & production of viral DNA

48
Q

Protease inhibitors

A

Inhibit processing of large viral proteins into individual components

49
Q

Fusion inhibitors

A

Prevent viruses from successfully fusing with the host cell

LSCI 230: Microbiology (14 decks)

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