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Microbial world > Lecture 13 and 14 > Flashcards

Lecture 13 and 14 Flashcards

1
Q

What was the first virus to be discovered?

A

Tobacco mosaic virus

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2
Q

What does tobacco mosaic virus do?

A

Causes tobacco leaves to be mottled, stunts growth

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3
Q

Who was the first person to investigate TM disease?

A

Adolf Mayer

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4
Q

What did Adolf Mayer find could transfer the disease?

A

Diseases could be transferred in sap between plant

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5
Q

What could Adolf Mayer not find?

A

Anything microscopic in the sap causing the disease (something submicroscopic was causing the disease)

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6
Q

Who filtered the sap?

A

Dmitri Ivanovsky

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7
Q

What did Dmitri Ivanovsky find when he filtered the sap?

A

It could still transfer the disease

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8
Q

What did the fact that filtered sap could transfer disease suggest?

A

It was sub-microscopic or a toxin

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9
Q

Who discovered that the disease could replicate and therefore was not a toxin:?

A

Martinus Beijerinck

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10
Q

How did Martinus Beijerinck conclude the virus can replicate?

A

Filtered sap causes mottled leaf appearance in a third plant- therefore toxin was not responsible for transmission

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11
Q

Who tried to culture bacteria from the infected tobacco plant?

A

Martinus Beijerinck

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12
Q

What did the fact that Beijerinck’s cultures didn’t grow suggest?

A

Disease not caused by cultivable bacteria

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13
Q

How did Beijerinck definitively show that tobacco mosaic disease was not caused by a bacterium?

A

He treated the sap with ethanol to damage the membrane. The sap was still infectious, therefore not bacteria

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14
Q

Who first isolated and crystallised TMV virion?

A

Wendell Stanley

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15
Q

What did Stanley’s crystallized virus remain?

A

Infectious

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16
Q

What did the fact that TMV remained infectious demonstrate?

A

Viruses have no independent metabolism

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17
Q

Who first viewed TMV virion? How?

A

Kausche, Pfankuch and Ruska

Electron microscope

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18
Q

What is the average virus size?

A

20nm diameter to 1000nm length

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19
Q

What is the cultivable nature of viruses?

A

Obligate intracellular parasites

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20
Q

What bacteria share small size and cultivatable nature of viruses?

A

Rickettsia/ Chlamydia

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21
Q

What is the cell structure of viruses?

A

No cellular structure (acellular)

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22
Q

What is the protein coat around a viruses genome called?

A

Capsid

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23
Q

What genome do viruses have?

A

A single type of nucleic acid (RNA or DNA)

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24
Q

What is a envelope?

A

A lipid layer surrounding the capsid

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25
Q

What does synthesis result in?

A

Specialised structures that transfer viral genome to other host cells

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26
Q

Generally, where do enveloped viruses come from?

A

Animal cells with no cell wall

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27
Q

Why can’t most drugs interfere with viral multiplication?

A

Would affect host cell function, host enzymes are used to generate the parasites

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28
Q

What name is given to viruses that infect fungi?

A

Mycoviruses

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29
Q

What host range do most viruses have?

A

Limited to usually one host species, specific cell types

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30
Q

What virus causes glandular fever?

A

Epstein-Barr virus

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31
Q

What phages infect Escherichia coli?

A

T-even phages (T2, T4)

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32
Q

What cells does influenza A virus infect?

A

Nose/throat/lungs epithelial cells

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33
Q

What cells does Epstein-Barr virus infect?

A

B-lymphocytes

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34
Q

Why is virus host range limited?

A

Virus requirements: specific receptor/ligand for cell invasion
Need certain host factors for viral replication

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35
Q

Name a virus that can jump species and expand their host range.

A

Influenza A virus (has several variants (serotypes))

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36
Q

What type influenza A serotype infects birds?

A

H7N7

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37
Q

What serotype of influenza A infects pigs?

A

H1N1, but can act as a reservoir for all serotypes

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38
Q

What serotype of influenza A virus infects humans?

A

H3N3

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39
Q

Why are emerging diseases a big problem?

A

No natural defenses: we haven’t adapted to these diseases

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40
Q

What are the 2 life cycle stages for viruses?

A

Replicating stage, birion

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41
Q

What is the replicating stage?

A

Genome replicating

Active, intracellular disease causing stage

42
Q

What is the virion stage?

A

Dormant, transmissible stage, survives outside host

43
Q

What is the core of a virion?

A

Nucleic acid (DNA or RNA)

44
Q

What is the capsid composed of?

A

Subunits called capsomeres

45
Q

What makes up the capsomeres?

A

Some viruses, made of one protein

Other viruses, capsomere made of several proteins

46
Q

How does the capsid get put together?

A

It is self assembling

47
Q

What gives the virus a shape?

A

The capsid

48
Q

What shape can viruses be?

A

Helical, complex, polyhedral

49
Q

How are capsomeres arranged in helical viruses?

A

Arranged in a spiral (coil like)

50
Q

What shape do capsomeres form in polyhedral viruses?

A

Equilateral triangle, which arrange into polyhedral

51
Q

Most polyhedral viruses are ______ shaped.

A

Icosahedral (20)

52
Q

What is the enveloped derived from?

A

Host membrane

53
Q

What can the envelope contain?

A

Glycoproteins (spikes) encoded by viral and host genome

54
Q

What do spikes on the envelope do?

A

Function as antigens: involved in host cell invasion and identification

55
Q

What is the other function of the envelope?

A

Protect virion from enzymes/chemicals

56
Q

Name two enveloped viruses

A

Influenza

HIV

57
Q

What viruses carry appendages?

A

Complex viruses (particularly bacteriophages)

58
Q

What do appendages do?

A

Used to attach virus to host cell

59
Q

Name a non-enveloped polyhedral virus.

A

Poliovirus

60
Q

Name an enveloped polyhedral virus

A

Herpes simplex virus

61
Q

Name a non-enveloped helical virus

A

TMV

62
Q

What shape are viral genomes?

A

Circular or linear (nucleic acid type irrelevant)

63
Q

Viral genomes can be _____ or __-______

A

Segmented

Non segmented

64
Q

What is a segmented viral genome?

A

Several nucleic acid molecules, such as some RNA viruses

65
Q

What are non-segmented viral genomes?

A

Single nucleic acid molecule (most DNA viruses, some RNA viruses)

66
Q

Single stranded (ss)RNA viruses can be:

A

+sense
or
-sense

67
Q

What is +ssRNA?

A

Can be translated directly by host cell

68
Q

What is -ssRNA?

A

Converted to +sense before translation

69
Q

How is the + strand made from the - strand?

A

RNA polymerase synthesises it

70
Q

What must -ssRNA also encode?

A

RNA polymerase

71
Q

What are two classification systems used to classify viruses?

A

International committee of taxonomy of viruses

Baltimore classification

72
Q

What does ICTV use?

A

Nucleic acid type, site of replication, morphology and pathology

73
Q

What is the taxonomic structure of viruses?

A

Order
Family
Genus
Species

74
Q

What does baltimore classification do?

A

Take into account unassigned viruses of ICTV

Based on how viruses generate mRNA

75
Q

What 7 groups are baltimore classified viruses split into?

A

dsDNA, ssDNA, dsRNA, +ssRNA, -ssRNA, +ssRNA-RT, dsDNA-RT

76
Q

Give an example of a virus that undergoes the lytic cycle.

A

T-even bacteriphage

77
Q

What are the 5 stages of the lytic cycle?

A 
Attachment
Penetration
Biosynthesis
Maturation
Release
78
Q

What enzyme degrades the cell wall of the host when the baseplate of the virus makes contact with the cell wall?

A

Lysozyme

79
Q

Gene expression is ______, it is not expressed at the same time

A

Temporal

80
Q

What are the early genes?

A

Viral genome replication

81
Q

What happens to host DNA?

A

Viral-induced degredation

82
Q

How does host protein biosynthesis stop?

A

Viral proteins interfere/repress host translation

83
Q

How long does the lytic cycle take?

A

About 30 minutes

84
Q

What enzyme breaks down bacterial cell wall during release?

A

Lysozyme

85
Q

Name a lysogenic phage.

A

E.coli bacteriophage lambda

86
Q

What are the 7 stages of lysogenic cycle?

A 
Attachment
Penetration
Integration/dormancy
Excision
Biosynthesis
Maturation
Release
87
Q

What is the first stage of integration?

A

The viral genome circularises

88
Q

What is the inserted viral DNA called?

A

Prophage

89
Q

Why are there differences between bacteriphages and animal viruses?

A

Envelope/non-envelope

Genome structure

90
Q

What are the 6 stages of animal virus replication?

A 
Attachment
Entry
Uncoating
Biosynthesis
Maturation
Release
91
Q

Uncoating in animal viruses means that…

A

can get dormancy phase for some animal viruses (latent disease)

92
Q

What are virion ligands in animal viruses?

A

Spikes (enveloped)

Fibres (non-enveloped)

93
Q

What happens during attachment of enveloped viruses?

A

Specific receptor/ligand interaction

94
Q

What happens during fusion entry of enveloped viruses?

A

Fusion: host cell membrane/viral envelope fuse, capsid released into cytoplasm

95
Q

What happens during endocytosis/pinocytosis entry of enveloped viruses?

A

Attachment can trigger endocytosis or ‘feeding’ mechanism pinocytosis

96
Q

What happens during uncoating?

A

Enzyme mediated degredation of capsid to release viral genome

97
Q

What may the uncoating enzyme be of?

A 
Viral origin (poxviruses)
Host origin
98
Q

How do non-enveloped viruses fuse?

A

Host cell membrane/viral capsid fuse, viral genome released into host cytoplasm

99
Q

Where do RNA viruses multiply in animals?

A

The cytoplasm

100
Q

What ways are animal viruses release?

A

Budding (enveloped), rupturing (non-enveloped viruses)

101
Q

How does budding work?

A

Capsid associates with and adheres to portion of the host plasma membrane to virus to form a bud

102
Q

What stages do antivirals attack?

A

Uncoating, viral biosynthesis (nucleic acid replication and protein processing)
Release

Microbial world (12 decks)

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