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Microbiology (Bio305) > Chapter 6 > Flashcards

Chapter 6 Flashcards

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Biology 101 flashcards
1
Q

What is a noncellular particle that must infect a host cell, where it reproduces?

A

Virus

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2
Q

What does a virion consist of?

A
  • a single nucleid acid

- contained in a capsid

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3
Q

Are viruses specific or general in what kind of host cell they can affect?

A 
- Specific; the hosts are 
  limited to a particular 
  host range of closely 
  related strains or 
  species
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4
Q

What is a virus that infects bacteria called?

A
  • bacteriophage
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5
Q

What is the measles virus?

A
  • a human virus
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6
Q

What is the TMV?

A
  • tobacco mosaic virus

- plant virus

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7
Q

What happens after a RNA virus infects the cell?

A
  • Virions are assembled within “virus factories”, virus-induced cell compartments called a replication complex
  • Complexes move around within the cell
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8
Q

Do viruses only replicate in the host?

A
  • No some integrate their genomes into that of the host
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9
Q

What is a prophage?

A
  • a virus the integrates its genome into the DNA of a bacterial genome
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10
Q

What is a provirus?

A
  • an integrated viral genome within a human cell
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11
Q

What is an endogenous virus?

A
  • a permanently integrated provirus transmitted via the germ line
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12
Q

What are the three different forms a virus may interconvert to?

A
  • Virion
  • Intracellular replication complex
  • Viral genome integrated within host DNA
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13
Q

What is the Virion form?

A
  • an inert particle that does not carry out any metabolism or energy conversion
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14
Q

What is the Intracellular replication complex form?

A
  • Within a host cell, the virla gene products direct the cell’s enzymes to asseble progeny virions at “virus factories” called replication complexes
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15
Q

What is the Viral genome integrated within host DNA form?

A
  • This may be a permanent condition
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16
Q

What type of virus is related to the lysogenic cycle?

A

provirus

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17
Q

Do viruses play a role in the ecosystem?

A

yes

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18
Q

How do acute viruses affect the ecosystem?

A 
- act as predators or 
  parasites to limit host 
  population density
- recycle nutrients from 
  their host bodies
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19
Q

How does Virus-associated mortality affect the ecosystem?

A
  • they may increase the
    genetic diversity of
    host species
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20
Q

How do persistent viruses affect the ecosystem?

A
  • they may evolve traits
    that confer positive
    benefits in a virus-host
    mutualism
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21
Q

What role do viruses play in marine ecosystems?

A 
- significant role in the 
  cycling of food 
  molecules
- also important in 
  carbon balance
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22
Q

What is a host range?

A
  • a particular group of
    host species that a
    virus can infect
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23
Q

Are chronic or acute virus disease more common?

A

Chronic

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24
Q

What keeps the viral genome intact and enables infection of the appropriate host cell?

A
  • the structure of the

virion

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25
Q

What delivers the viral genome to the host cell?

A
  • the capsid
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26
Q

What are Icosahedral viruses?

A 
- polyhedral with 20 
  identical triangular 
  faces
- have a structure that 
  exhibits rotational 
  symmetry
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27
Q

What encloses some icosahedral viruses?

A

envelope

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28
Q

What does this envelope contain?

A 
- glycoprotein spikes 
  (encoded by the virus) 
- Tegument proteins (in 
  between the   
  envelope and capsid)
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29
Q

What are Filamentous viruses?

A 
- capsid consists of a 
  long tube of protein 
  with genome coiled 
  inside
- vary in length 
  depending on genome 
  size
- include bacteriophages 
  as well as animal 
  viruses
- show helical symmetry
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30
Q

What is an example of a tailed virus?

A
  • T4 bacteriophages
  • Has an icosahedral
    “head” and helical
    “neck”
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31
Q

What are RNA viruses that lack capsid symmetry?

A
  • Influenza viruses
  • RNA segments are
    coated with
    nucleocapsid proteins
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32
Q

What is special about Poxviruses?

A 
- Their genome is 
  surrounded by several 
  layers.
- large number of 
  accessory proteins
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33
Q

What contains so many enzymes that they appear to have evolved from degenerate cells?

A
  • Large asymmetrical

viruses

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34
Q

What are RNA molecules that infect plants?

A

Viroids

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35
Q

What are some characteristics of viroids?

A
  • no protein capsid
  • replicated by host
    RNA polymerase
  • catalytic ability
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36
Q

What are proteins that infect animals?

A
  • Prions
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37
Q

What are some characteristics of prions?

A 
- no nucleic acid 
  component
- abnormal structure 
  that alters the 
  conformation of other 
  normal proteins
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38
Q

Viral genomes can be:

A
  • DNA or RNA
  • Single or double-
    stranded
    -Linear or circular
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39
Q

What has key consequences for the mode of infection, and for the course of a viral disease?

A
  • the form of the

genome

40
Q

What is the criteria that viruses are classified by?

A
  • Genome Composition
  • Capsid Symmetry
  • Envelope
  • Size of the virion
  • Host range
41
Q

David Baltimore proposed that the main distinctions among classes of viruses be:

A
  • genome composition
  • the route used to
    express messenger
    RNA
42
Q

Group I

A

Double-stranded DNA viruses

43
Q

Group II

A

Single-stranded DNA viruses

44
Q

Group III

A

Double-stranded RNA viruses

45
Q

Group IV

A

(+) single stranded RNA viruses

46
Q

Group V

A

(-) single stranded RNA Viruses

47
Q

Group VI

A

RNA retroviruses

48
Q

Group VII

A

DNA paraetroviruses

49
Q

How can the relatedness of different herpes viruses that evolved from a common ancestor be measured?

A
  • by comparing their

genome sequences

50
Q

What is this comparison based on?

A
  • Orthologs
  • Genes of common
    ancestry in two
    genomes that share
    the same function
51
Q

What is useful for viruses because of their small genomes encode few proteins?

A
  • Proteomic

classification

52
Q

What are gut bacteriophages called?

A
  • Coliphages
  • modulates human
    digestion, the
    immune system, and
    mental health
53
Q

What is mediated by cell-surface receptors?

A
  • Contract and

attachment

54
Q

What are cell-surface receptors?

A 
- Proteins that are 
  specific to the host 
  species and which 
  bind to a specific viral 
  component
- normally used for 
  important functions for 
  the host cell
55
Q

True or False. Most bacteriophages inject only their genome into a cell through the cell envelope.

A

True

56
Q

What are the two different life cycles that bacteriophages can undergo?

A 
- Lytic Cycle: Virulent 
  Phage( kills host) ex) 
  T4
- Lysogenic cycle:  
  Temperate Phage
  (forms prophage)
57
Q

Steps of the Lytic replication cycle:

A 
1. host recognition and 
   attachment
2. Genome Entry
3. Assembly of phages
4. Exit and transmission
58
Q

What is a temperate phage?

A 
- can infect and lyse 
  cells like a virulent 
  phage, but it also has 
  an alternative 
  pathway: to integrate 
  its genome as a 
  prophage
59
Q

What is the state called lysogeny?

A
  • Bacteriophage is
    quiescent
  • Can reactivate to
    become lytic
60
Q

How does a slow-release replication cycle differ from lysis and lysogeny?

A
  • phage particles reproduce without destroying the host cell.
61
Q

What extrudes individual progeny through the cell envelope?

A
  • Filamentous phages
62
Q

What are three types of defense mechanisms that bacteria have?

A
  • genetic resistance
  • restriction endonucleases
  • CRISPR
63
Q

What is genetic resistance?

A
  • altered receptor proteins
64
Q

What is restriction endonucleases?

A
  • Cleave viral DNA lacking methylation
65
Q

What is CRISPR?

A
  • Clustered regularly interspaced short palindromic repeats

- A bacterial immune system of sorts

66
Q

What is the best understood phage community?

A

Gut Virome

67
Q

Phage effects that are positive:

A
  1. Phages may limit the bacterial numbers to levels that the human immune system can tolerate.
  2. Phage particles may modulate immune system activity by suppressing T-cell activation and tumor formation.
  3. Phages may attack biofilms
68
Q

What determines Tropism?

A
  • the receptors of the cell`
69
Q

How do most animal viruses enter the host as?

A
  • Mostly as virions

- Internalized virions undergo uncoating, where genome is released from its capsid.

70
Q

What is the primary factor determining the life cycle of an animal virus?

A
  • the form of its genome
71
Q

Replication Cycle: DNA Viruses

A
  • can utilize the host replication machinery
72
Q

Replication Cycle: RNA Viruses

A
  • Use an RNA-dependent RNA-polymerase to transcribe their mRNA
73
Q

Replication Cycle: Retroviruses

A
  • Use a reverse transcriptase to copy their genomic sequence into DNA for insertion in the host chromosome
74
Q

True or False. All animal viruses make proteins with host ribosomes.

A

True

-Translation occurs in the cytoplasm

75
Q

Assembly of new virions

A
  • Capsid and genome
  • May occur in the cytoplasm or nucleus
  • Envelope proteins are inserted into a membrane
76
Q

What happens when the release of progeny viruses from host cell happens?

A
  • Lysis of cell

- Budding

77
Q

What happens during Budding?

A
  • Virus passes through membrane
  • Membrane lipids surround capsid to form envelope
  • All enveloped viruses bud from a membrane
    (plasma or organelle membrane)
78
Q

What virus causes many human cancers?

A
  • Oncogenic Viruses
79
Q

What does an Oncogenic Virus do to the host cell?

A
  • it transforms it to become cancerous
80
Q

What are the mechanisms of oncogenesis?

A
  • Insertion of an oncogene into the host genome
  • Integration of the entire viral genome
  • Expression of viral proteins that interfere with host cell cycle regulation
81
Q

Entry of plant viruses into host cells usually requires…..

A
  • mechanical transmission
82
Q

What are the three routes that plant viruses enter?

A
  • Contact with damaged tissues
  • Transmission by an animal vector
  • Transmission through seed
83
Q

What prevents a lytic burst or budding out of virions in a plant?

A
  • thick cell walls
84
Q

Instead of this plant viruses are transmitted to uninfected cells by…

A

-plasmodesmata

85
Q

What is plasmodesmata?

A
  • Membrane channels that connect adjacent plant cells

- Inner channel connects the ER

86
Q

Since viruses are ubiquitous what are three defense mechanisms that animal and plants have?

A
  • Genetic Resistance
  • Immune System
  • RNA interference (RNAi)
87
Q

What is genetic resistance?

A
  • Host continually experiences mutations
88
Q

What is the immune system?

A
  • “inactive immunity”: interferons

- “Adaptive immunity”: antibodies

89
Q

What is the RNA interference?

A
  • Widespread among eukaryotes and archaea
90
Q

What is the RNA interference?

A
  • Widespread among eukaryotes and archaea
91
Q

How does a “new” virus emerge to sicken humans?

A
  1. As a result of human consumption of wildlife

2. As variants of endemic milder pathogens

92
Q

What requires growth in host cells?

A
  • Culturing Viruses
93
Q

Bacteriophages may be cultured in….

A
  • batch culture(in liquid)

- isolated plaques on a bacterial lawn (on a plate)

94
Q

What generates a step curve?

A

-Batch culture of viruses

95
Q

What can be cultured within the whole organism by serial inoculation?

A
  • Animal Viruses
96
Q

What does serial inoculation ensure?

A
  • that the virus strain maintains its original virulence, but the process is expensive and laborious
97
Q

What is the alternative way to grown animal viruses?

A
  • In human cell tissue culture

Microbiology (Bio305) (7 decks)

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