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Final D&D > Virus Properties > Flashcards

Virus Properties Flashcards

1
Q

LO 1. Define the basic properties of viruses.

A

submicroscopic, obligate intracellular parasites; not alive;

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2
Q

LO 2. List the strategies viruses employ for survival.

A
  1. house genetic info w/I capsids
  2. genome contains all info needed to initiate and complete an infectious cycle
  3. establish a relationship with a host, from benign to lethal
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3
Q

LO 3. Describe 2 means of classifying viruses.

A
  1. the Classical System (grouped by shared physical properties)
  2. the Baltimore System (by the way they produce mRNA)
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4
Q

LO 4. Understand basic methods for studying viruses.

A 
electron microscopy 
cell culture 
animal models 
sequence analysis 
serology 
other molecular techniques
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5
Q

LO 5. Identify the main structural characteristics of virus particles.

A

capsids, envelopes, genetic info (DNA, RNA, or both)

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6
Q

LO 6. Describe the 7 basic virus genomes, protein expression strategies, and replication strategies of each

A
  1. dsDNA (use the - strand as template, RNA pol II, in nucleus or cytoplasm)
  2. gapped circular dsDNA (uses a protein as part of its pol machinery)
  3. ssDNA (ds intermediate made in nucleus)
  4. dsRNA
  5. ss(+)RNA (RNA-dependent RNA pol (RdRp)
  6. ss(-)RNA (also use RdRp)
  7. ss(+)RNA with DNA intermediate (copy their ssRNA into DNA first using reverse transcriptase)
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7
Q

LO 7. Describe a typical, generalized replication cycle of a virus.

A
  1. attachment
  2. entry and uncoating
  3. viral gene expression
  4. viral genome replication
  5. assembly of new viruses and egress of these from the cell
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8
Q

Viruses house their DNA or RNA genomes in small proteinaceous particles called _____.

A

capsids

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9
Q

Name 2 capsid shapes.

A
  1. helical

2. Isosahedral

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10
Q

What is the Classical System?

A

grouping viruses by their shared physical characteristics (type of genome, capsids, naked or enveloped, dimensions)

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11
Q

What is the Baltimore System?

A

categorizes viruses based on how they produce mRNA

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12
Q

What is the (+) strand?

A

mRNA that has an open reading frame- it’s ribosome ready and able to be translated into protein

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13
Q

What is the (-) strand?

A

complementary mRNA seq that is not directly translated to mRNA, but is used to make DNA

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14
Q

What are the 2 key principles of viral genomes?

A
  1. Genomes serve as the template for synthesis of progeny genome (small, finite # of nucleic acid copying strategies)
  2. viral genomes have to provide mechanisms for making mRNA
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15
Q

What are the 2 key principles of viral genomes?

A
  1. Genomes serve as the template for synthesis of progeny genome (small, finite # of nucleic acid copying strategies)
  2. viral genomes have to provide mechanisms for making mRNA
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16
Q

What is a helical capsid?

A

has rotational symmetry; arranges irregularly-shaped proteins in a circle to form a disk

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17
Q

What is an icosahedral capsid?

A

proteins arranged to form a hollow, quasi-spherical structure with genome inside it; 20 triangular faces

18
Q

What is an envelope?

A

lipid bilayers with viral glycoproteins embedded in the membrane that viruses acquire by budding thru a host membrane

19
Q

Why are envelopes important?

A

enveloped viruses don’t necessarily kill their host cells during replication, but non-enveloped viruses almost always do

20
Q

Why are viral glycoproteins important?

A

they mediate entry and to specific hosts, assembly and egress, and evasion from immune systems

21
Q

Describe the viral growth curve.

A
  1. eclipse period (0-12 hours; no detectable infection inside or out of the cell)
  2. latent period (16 hours; time it takes from initial infection to release of new viral particles)
  3. burst (sudden increase of PFUs)
22
Q

What happens during the latent period?

A

attachment, entry, uncoating, gene expression, genome replication, assembly, and egress

23
Q

What is attachment?

A

binding of viral-attachment protein to a cellular receptor, which can be protein (specific) or carbohydrate (less-specific)

24
Q

What is entry?

A

penetration of the virus into the target cell. Energy dependent- cell must be metabolically active. Endocytosis or viral envelope fusion.

25
Q

How do enveloped viruses gain entry?

A

viral envelope fuses with the plasma membrane or endocytic membranes; requires the presence of a specific fusion protein

26
Q

What is uncoating?

A

once inside the cell, the viral particle loses its capsid and viral genome exposed

27
Q

How do DNA viruses express their genes?

A
  1. fill (-) strand DNA using host’s DNA pol 2 in the nucleus
  2. transcribe normal mRNA
    * ** exception: poxviruses replicate in cytoplasm and encode their own RNA pol
28
Q

How do RNA viruses express their genes?

A
  1. fill (-) strand DNA using host’s DNA pol 2 in the nucleus
  2. transcribe normal mRNA
    * ** exception: poxviruses replicate in cytoplasm and encode their own RNA pol
29
Q

How do RNA viruses express their genes?

A

all have their own RNA-dependent RNA pol (RdRp) to produce mRNA and replicate RNA genomes

30
Q

How do (+) stranded RNA viruses express their genes?

A

direct translation by cellular ribosomes; amplification via RdRp

31
Q

How do (-) stranded RNA viruses and ds RNA viruses express their genes?

A

must transcribe (+) sense mRNA first by using RdRp

32
Q

How do retroviruses express their genes?

A

first copy ssRNA into dsDNA using reverse transcriptase; integrate new dsDNA into host genome; transcribe mRNA using host RNA pol 2

33
Q

What is assembly?

A

packaging of the genome into capsids

34
Q

Name 2 ways icosahedral capsids can package their genomes.

A
  1. capsid assembles around the genome

2. genome is fed into preformed capsids

35
Q

How do helical capsids package their DNA?

A

genome is coated with nucleocapsid protein during its synthesis

36
Q

What does CPE stand for?

A

cytopathic effect

37
Q

What is CPE?

A

capsid proteins produced in such high amounts that they are visible as cytoplasmic or nuclear inclusions on light microscopy; size and location characteristic of particular virus

38
Q

What is egress?

A

exit from the infected cell

39
Q

How do enveloped viruses egress?

A

budding (from plasma membrane = into extracellular environment; from Golgi or ER = secreted from cell)

40
Q

How do naked viruses egress?

A

cell lysis

Final D&D (16 decks)

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