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Bmsc 210- M2 > Chapter 8- Viruses and Virology > Flashcards

Chapter 8- Viruses and Virology Flashcards

1
Q

Virus

A

genetic element that cannot replicate independently of a living cell (host)

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2
Q

Virology

A

the study of viruses

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3
Q

Virus particle (virion)

A

extracellular form of a virus

  • exists outside host and facilitates transmission from one host cell to another
  • contains nucleic acid genome surrounded by a protein coat and in some cases other layers of material
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4
Q

Classes of Viruses

A 
based on the hosts that they infect
- Bacteria (bacteriophage)
- Archaeal viruses
- Animal viruses
- Plant viruses
-
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5
Q

size of viruses

A

usually smaller than prokaryotic cells; 0.02 to 0.3 µm

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6
Q

Capsid

A

the protein shell that surrounds the genome of a virus particle
- composed of a number of protein molecules arranged in a precise and highly repetitive pattern around the nucleic acid

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7
Q

Capsomere

A

Subunit of the capsid

- smallest morphological unit visible with an electron microscope

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8
Q

Nucleocapsid

A

complete complex of nucleic acid and protein packaged in a virion

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9
Q

Enveloped virus

A

virus that contains a membrane around the nucleocapsid
- envelope makes initial contact with host cell
(‘naked’ doesn’t have a membrane- most bacteriophage are naked)

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10
Q

Helical symmetry

A

rod-shaped viruses

  • length of virus determines by length of nucleic acid
  • width of virus determined by size and packaging of protein subunit
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11
Q

Icosahedral symmetry

A

spherical viruses

- most efficient arrangement of subunits in a closed shell

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12
Q

Influenze virus

A

the envelop contains rigid spikes of haemagglutinin and neuraminidase which form a characteristic halo of projections around negatively stained virus particles

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13
Q

Complex virus

A

Virions composed of several parts, each with separate shapes and symmetries
- Bacterial viruses (Icosahedral heads and helical tails)

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14
Q

Some virions contains enzymes critical to infection:

A
  • lysozyme- makes hole in cell wall, lyses bacterial cell
  • nucleic acid polymerases
  • neuraminidases- enzymes the cleave glycosidic bonds; allows liberation of viruses from cell
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15
Q

Titer

A

number of infectious units per volume of fluid

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16
Q

Plaque Assay

A

analogous to the bacterial colony; one way to measure virus infectivity

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17
Q

placques

A

are clear zones that develop on lawns of host cells

lawn can be bacterial or tissue culture, each plaque results from infection by single virus particle

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18
Q

Efficiency of planting

A

is used in quantitative virology
- # of plaque forming units is almost always lower than direct counts by electron microscopy due to: inactive virions, conditions not appropriate for infectivity

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19
Q

Which viruses are easiest to grow

A

bacterial viruses

20
Q

which viruses are the most difficult to study

A

plant viruses- study often requires growth of whole plant

21
Q

5 Phases of Viral Replication

A
  1. Attachment.. of a virus to a susceptible host cell
  2. Entry.. of the virion or its nucleic acid
  3. Synthesis.. of virus nucleic acid and protein by cell metabolism as redirected by virus
  4. Assembly.. of capsids and packaging of viral genomes into new virions (maturation)
  5. Release.. of mature virions from host cell
22
Q

One step growth curve:

latent period vs burst size

A

latent- eclipse and maturation

burst size- number of virions released

23
Q

Permissive Cell

A

host cell that allows the complete replication cycle of a virus

24
Q

T4

A

one of the most complex penetration mechanisms

  • T4 attaches to cells via tail fibres that interact with polysaccharides on the E.coli envelope
  • Tail fibres react and tail core males contact with E.coli cell wall
  • Attachment of virus to its host cell results in changes to both virus and cell surface that facilitate penetration
  • Lysozyme-like enzyme forms mall pore in peptidoglycan
  • Tail sheath contracts and viral DNA passes into cytoplasm
25
Q

Mechanisms to Diminish Viral Infections

A
  • Immune defense mechanisms, RNA interference
  • Restriction modification systems (only effective against double stranded DNA viruses, modification of hosts own DNA at RE recognition sites prevents cleavage of its DNA)
26
Q

Viruses can evade bacterial restriction system by:

A
  • chemical modification of viral DNA

- production of proteins that inhibit host cell RE system

27
Q

Permissive cell

A

host cell that allows the complete replication cycle of a virus to occur

28
Q

T4 genome

A

contains the modified base 5-hydroxymethylcytosine DNA that is resistant to virtually all known RE
- has a dsDNA genome that is circularly permuted and terminally redundant (which both affect genome packaging)

29
Q

Circularly permuted

A

circular permutation is a relationship between proteins whereby the proteins have a changed order of amino acids in their peptide sequence. The result is a protein structure with different connectivity, but overall similar three-dimensional (3D) shape

30
Q

Terminally redundant

A

DNA that contains repeated sequences at each end called terminal repeats)

31
Q

Genome packaging

A

a fundamental process in a viral life cycle. Many viruses assemble preformed capsids into which the genomic material is subsequently packaged. These viruses use a packaging motor protein that is driven by the hydrolysis of ATP to condense the nucleic acids into a confined space

32
Q

Three parts of T4 genome

A
  • Early- enzymes needed for DNA replication and transcription
  • Middle- same as early
  • Late- head and tail proteins and enzymes required to liberate mature phage particles
33
Q

Packaging of T4 genome

A
  • precursors of bacteriophage head os assembled
  • packaging motor os assembled
  • dsDNA is pumped into head under pressure using ATP
  • After head is filled with DNA, T4 tail, tail fibres and other components are added
34
Q

Virulent mode

A

viruses lyse host cell after infection

35
Q

Temperate mode

A

viruses replicate their genomes in tandem with host genome and without killing host
(virus can also be lytic)

36
Q

Temperate viruses

A

can undergo a stable genetic relationship within the host (but can also kill cells through lytic cycle)

37
Q

Lysogeny

A

state where most virus genes are not expressed and virus genome (prophage) is replicated in synchrony with host chomosome

38
Q

Lysogen

A

a bacterium containing prophage

39
Q

Bacterial Viral Diversity

A
  • diverse
  • most have dsDNA
  • most are naked
  • ## can be structurally very complex
40
Q

Animal Virus Diversity

A
  • entire virion enters cell
  • nucleus is the site of replication
  • contain all knwon modes of viral replication
  • many more kind of enveloped animal viruses
41
Q

Animal DNA vs RNA viruses

A

DNA- ds, ss, non-enveloped, enveloped, different shapes and sized
RNA- all enveloped viruses are ss, nonenveloped can be ss or ds, different shapes and sizes

42
Q

Persistant infections

A
  • release of virions from host cell does not result in cell lysis
  • infected cell remain alive and continues to produce virus
43
Q

Latent infections

A

delay between infection by the virus and lytic events

44
Q

transformation

A

conversion of normal cell into tumor cell

45
Q

cell fusion

A

two or more cells become one cell with many nuclei

Bmsc 210- M2 (4 decks)

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