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Microbiology > Chapter 13 - Viruses, Viroids, Prions > Flashcards

Chapter 13 - Viruses, Viroids, Prions Flashcards

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1
Q

True or false? Viruses are obligate intracellular parasites

A

True

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2
Q

What are Viruses?

A

inert particles outside host cells

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3
Q

How to Viruses work?

A

Their genome hijacks the host cell’s replication machinery and directs activities of the cell

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4
Q

Are Viruses living?

A

NO

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5
Q

Where is the genetic information contained? What is it?

A

DNA or RNA within a protected coat

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6
Q

What is the typical size for viruses?

A

SMALL. 10nm & 10 genes ~ 500nm

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7
Q

What two components make up Naked viruses?

A

Nucleic acid and the capsid (lack envelope)

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8
Q

True or False? Naked viruses are more resistant to disinfectant.

A

True

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9
Q

What are the three components of Enveloped viruses?

A

Nucleic acid, capsid, envelope

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10
Q

What is the capsid-nucleic acid complex called?

A

Nucleocapsid

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11
Q

What are possible characteristics of viral nucleic acid/genomes?

A

DNA or RNA, Linear or Circular or Fragmented, Double or Single-stranded

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12
Q

What is the Capsid and what is it made up of?

A

It is a protein coat made up of identical subunits called capsomers (shape of the virus)

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13
Q

What is the envelope?

A

A lipid layer

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14
Q

Where are spikes seen on viruses?

A

Animal Viruses

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15
Q

Where are tail fibers seen?

A

Phage

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16
Q

What are the three possible Viral shapes?

A

Icosahedral, Helical, and Complex

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17
Q

How are Viruses named?

A

families end in -viridae and genus ends in -virus * the species name is often the mane of the disease *commonly referred to only by species name

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18
Q

What are the three types of Bacteriophages?

A

Lytic, Temperate, Filamentous

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19
Q

What is another term for a lytic phage?

A

virulent

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20
Q

What do Lytic phages do?

A

Infect host cells, use productive infection to make new phage subunits, assemble them, and lyse cells releasing new phage (30 min)

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21
Q

What is the 5 step process of Lytic Phages?

A

1-Attachment 2-Genome entry 3-Synthesis 4-Assembly 5-Release

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22
Q

What happens in the attachment stage?

A

Phage exploits receptors on cell wall and tail fibers are used

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23
Q

What happens in Genome Entry?

A

T4 lysozome degrades bacterial cell wall and the tail contracts and injects genome through the cell wall and membrane

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24
Q

What happens in the Synthesis of proteins and genome?

A

The early proteins are translated within minutes and late proteins are produced near the end of the cycle

*The early proteins degrade host DNA and the proteins modify host’s RNA polymerase to not recognize its own promoters

*The late proteins are structural proteins (capsid, tail, etc.)

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25
What happens during Assemply?
Some of the components assemble spontaneousy and other need protein scaffolds
26
What happens during the release?
Lysozyme is produced late in the infection and digests the cell wall \*Cell lyses and phages are released Burst size of T4 is ~200
27
What is the special characteristic of Temperate phages?
They have the option of undergoing a lytic infection or lysogenic infection
28
What is a Lysogenic infection?
The incorporation of phage DNA into host cell genome where the phage remains latent
29
What is the infected cell by a temperate phage called?
lysogen
30
What serves as the model for a temperate phage?
Lambda
31
What is the integrated phage DNA called?
prophage
32
What prevents lytic infection in temperate phages?
A repressor
33
About how many times is the DNA of the Lambda phage excised from the chromosome of the lysogen?
once per 10000 divisions of the lysogen
34
What happens if the DNA of a lysogen is damaged?
a protease is activated and repairs it
35
How does a temperate phage enter the lytic cycle?
Protease destroys the repressor and allows the prophage to be excised and it enters the lytic cycle
36
What is the change to the lytic cycle called?
phage induction \*allows phage to escape a damaged host
37
What are some advantages of Temperate phage infections?
1. The give partial immunity because the lysogen is immune to superinfection (infection by same phage) 2. The ability of lysogenic conversion, change in phenotype of lysogen from prophage (toxins encoded by phage genes and only strains carrying the prophage produce toxins)
38
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39
What are filamentous phages?
Single stranded DNA phages that look like long filaments
40
What do filamentous phages do?
Cause productive infections where host cells are not killed by lysis, but they grow more slowly
41
What is the phage model for the filamentous phage?
M13
42
How do filamentous phages enter cells?
Attaches to protein on F pili of E. Coli and the single stranded DNA genome enters the cytoplasm
43
How is the genome of the M13 generated?
The DNA polymeras of the host synthesizes complimentary DNA strand and one is used as synthesis for mRNA and other used for copies of the genome
44
How are new filamentous phages formed?
Phage coat protein molecules are inserted into the host cytoplasmic membrane and other proteins form pores \*The phage DNA is excreted through pores and coat proteins coat the DNA and form nucleocapsids
45
What are the 5 steps of Animal Virus infection?
1. Attachment 2. Penetration and uncoating 3. Synthesis 4. Assembly 5. Release
46
What happens during the attachment stage of animal virus infection?
Viruses bind to receptors, usyally glycoproeins on plasma membrane of the eukaryotic cell host \*specific receptors required
47
What happens during the Penetration and uncoating stage of animal virus infection?
Fusion or endocytosis
48
What happens during fusion?
1. Adsorption - Spikes of virion attach to specific host cell receptors 2. Membrane fusion envelope of virion fuses with plasma membrane 3. Nucleocapsid released into cytoplasm and the Viral envelope remains a part of the plasma membrane 4. Uncoating - Nucleic acids seperate from capsid 5. Virion and host cell membrane fuse
49
What happens during Endocytosis?
1. Adsorption - Attachment to the receptors triggers endocytosis 2. Endocytosis - Plasma membrane surrounds the virion and forms an endocytic vesicle 3. Release from Vesicle - Envelope of virion fuses with the endosomal membrane 4. Uncoating - Nucleic acid separates from capsid
50
What can Naked viruses NOT do?
Use the fusion process for entry
51
What happens during the Synthesis stage of animal virus infection?
The viral genes are expressed to produce viral structure \*multiple copies of the viral genome are synthesized
52
What is unique to replicaton of DNA viruses?
It usually takes place in the nucleus
53
What is unique of RNA virus replication?
Mostly single stranded and replicate in cytoplasm \*require virally encoded RNA polymerase (replicase) which lacks proofreading and allows antigenic drift
54
What is unique to replication of reverse-transcribing viruses?
They encode reverse transcriptase: Make DNA from RNA \*Retroviruses have ss (+) RNA genome (ex. HIV) \*the reverse transcriptase synthesizes single DNA strand \*A complimentary strand is synthesized; dsDNA is integrated into host cell chromosome and can be productive or latent
55
What happens during the assembly of animal virus infection?
Protein capsid forms and the genome is packaged
56
How is the release performed in the animal virus infection cycle?
Most are released via budding \*viral proteins insert into host cell membrand and nucleocapsids extruded \*covered with lipid envelope \*some get envelope from organelles \*naked viruses are released when host cell dies often by apoptosis initiated by virus or host
57
What are the two categories of Animal virus infections?
Acute and Persistent
58
What are the characteristics of Acute infections?
Rapid onset with short duration
59
That are the characteristics of Persistent infections?
They continue for years or a lifetime \*may or may not have symptoms \*some exhibit both (HIV)
60
What are the two categories of Persistent infections?
Chronic or latent
61
What is a chronic infection?
continuous production of low levels of virus particles
62
What is a latent infection?
viral genome (provirus) remains silent in host cell \*cannot be eliminated \*can be reactivated later
63
What do Proto-oncogenes and tumor suppressor genes do?
stimulate, inhibit growth and cell division
64
What do viral oncogenes do?
interfere with host control mechanisms and can induce tumors
65
How are animal viruses cultivated and quantitated?
Historically was done using innoculated live animals \*then used fertilized chicken eggs \*cell cultures or tissue cultures now used - can process animal tissues to obtain primary cultures - cells divide only a limited number of times - tumor cells are often used because they multiply indefinitely
66
How are plaque assays used?
To quantitate phage particles in samples
67
What are zones of clearing from bacterial lysis called?
Plaques
68
What is a titer?
the plaque forming units
69
What are Viroids?
small single stranded RNA molecules \*246-375 nucleotides \*only found in plants and enter through wound sites
70
What are prions?
proteinaceous infectious agents composed solely of protein \*NO NUCLEIC ACID \*linked to slow, fatal human and animal diseases \*usually only transmissible within species \*mad cow disease
71
Where do prions accumulate?
in the neural tissue \*neurons die, tissues develop holes, brain function deteriorates \*transmissible spongiform encephalopathies (general term for all prion diseases)
72
How does a prion infection happen?
Cells produce normal form: PrPC (prion protein, cellular) Infections prion Proteins: PrPSC (prion protein, scrapie) Resistant to proteases and become insoluble and aggregate Unusually resistant to heat and chemical treatments It is hypothesized that PrPSC converts PrPC folding to PrPSC
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Microbiology (9 decks)

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