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BMSC 210 > 14- Chapter 8 > Flashcards

14- Chapter 8 Flashcards

1
Q

What is a virus, virology, and a virus particle (virion)?

A

Virus- Genetic element that can not replicate independently of a living host
Virology- study of viruses
Virus particle (virion)- extracellular form of a virus (exists outside host and facilitates transmission from one host to another and contains nucleic acid genome surrounded by protein coat)

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2
Q

What are the general properties of viruses/viral genomes? (What about ssRNAs)

A

Viral genomes comprise either DNA or RNA
Some are circular but most are linear
RNA viruses can contain +ssRNA that can be directly read by ribosomes to synthesize viral proteins
viruses containing -ssRNA must use the -ssRNA as a template for the synthesis of +ssRNA before viral proteins can be made

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3
Q

What are the 5 classifications of viruses?

A
  1. Bacterial viruses (bacteriophages)
  2. Archaeal viruses
  3. Animal viruses
  4. Plant viruses
  5. Other (new classifications are based on nucleic acid similarities)
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4
Q

What is the structure of the virion?

A

Viruses come in many shapes and sizes
Usually smaller than prokaryotic cells (0.02 to 0.3 μm)

Almost all viral genomes are smaller than those of cells

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5
Q

What is the capsid, capsomere, nucleocapsid, and enveloped virus in the viral structure?

A

Capsid- the protein shell that surrounds the genome of the virus particle (composed of number of protein molecules arranged in precise and repetitive pattern)
Capsomere- subunit of capsid (smallest unit visible with microscope)
Nucleocapsid- complete complex of nucleic acid and protein packaged in the virion
Enveloped virus- virus that contains additional layers around the nucleocapsid
Slide 10 and 11

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6
Q

What is the nucleocapsid structure?

Helical and icosahedral symmetry

A

Nucleocapsids constructed in highly symmetric ways
Helical symmetry- rod shaped viruses (length is determined by length of nucleic acid, width is determined by size and packaging of protein subunits)
Icosahedral symmetry- spherical viruses (most efficient arrangement of subunits in a closed shell)
Slide 13

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7
Q

What is the structure of enveloped viruses?

A

Have membrane surrounding nucleocapsid (lipid bilayer with embedded proteins)
Envelope makes initial contact with host cell
Example on slides 14-15

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8
Q

What is the structure of complex bacterial viruses?

A

Virions composed of several parts, each with separate shapes and symmetries
Bacterial viruses contain complicated structures, icosahedral heads and helical tails

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9
Q

How are bacteriophages diverse?

A

Most phases contain dsDNA genomes
Most are naked, not all
Can be very structurally complex
Slide 17-18

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10
Q

What are the 3 types of enzymes virions May contain?

A
  1. Lysozyme-like- makes hole in cell wall, lyses bacterial cell
  2. Nucleic acid polymerases- RNA virus, RNA dependant RNA polymerase, also called RNA replicase
    Reverse transcriptase (retroviruses)
  3. Neuraminidases (influenza virus)- enzymes that cleave glycosidic bonds that allow liberation of viruses from cell
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11
Q

What is titer, plaque assay, and efficiency of plating in the quantification of viruses?

A

Titer- number of infectious units per volume
Plaque assay- analogous to the bacterial colony; one way to measure virus infectivity
Plaques are clear zones that develop on lawns of host cells (lawns can be bacterial or tissue culture
Efficiency of plating- used in quantitative virology where number of plaque forming units in almost always lower than direct counts by electron microscopy due to inactive virions and inproper conditions for Infectivity
Slide 21-22

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12
Q

What are the animal viruses, plant viruses and bacterial viruses ability to grows trends?

A 
Bacterial viruses are easiest to grow; model systems
Animal viruses (and some plant) can be cultivated in tissue or cell cultures
Plant viruses typically are most difficult because study often requires growth if whole plant
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13
Q

What are the 5 phases of viral replication?

A
  1. Attachment (absorption) of the virus to a susceptible host cell
  2. Entry (penetration) 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
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14
Q

What is the one step growth curve?

A

Latent period- eclipse and maturation
Burst size- number of virions released
Slide 25

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15
Q

How is the virion attached to host cell?

What is a permissive cell?

A

Highly specific, complementary receptors on surface of host and its infecting virus
Cellular receptors carry out cellular functions
They can be proteins, carbs, lipids, etc
Viral attachment to a host cell causes changes to virus and cell surface facilitating penetration

Permissive cell is a host cell that allows the complete replication cycle of a virus

Receptors on slide 28

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16
Q

How are viruses attached and entered? (5 steps E. coli)

A

Complex penetration mechanism
1. T4 attaches to cells by rail fibers which interact with polysaccharides on E coli cell envelope
2. Tail fibers retract and tail core makes contact with E. coli cell wall
3. Attachment of virus to host makes changes in virus and cell surface which facilitates penetration
4. Lysozyme like enzyme forms small pore in peptidoglycan
5. Tail sheath contracts and viral DNA passes into cytoplasm
Slide 30

17
Q

What are mechanisms to diminish viral infections?

How can viruses evade bacterial restriction enzymes?

A

Many eukaryotes and prokaryotes posses these mechanisms to defend against viral infections
Immune defense mechanisms
Restriction modification systems (only effective against double strand DNA viruses)

Viruses can evade bacterial restriction enzymes by chemical modification of viral DNA and production of proteins that inhibit host cell RE systems

18
Q

How is the T4 genome divided?

A

Early, middle, late genes
Early and middle proteins: enzymes needed for DNA replication and transcription
Late proteins: head and tail proteins and enzymes required to liberate mature phage particles
Slide 33-34

19
Q

How is the T4 genome packaged? (4 steps)

A
  1. Precursor bacteriophage head is assembled
  2. Packaging motor is assembled
  3. Double stranded DNA is pumped into head under pressure using ATP
  4. After head is filled with DNA, T4 tail, tail fibers, and other components are added
    Slide 36
20
Q

What are temperate viruses?
Lysogeny?
Lysogen?

A

Temperate viruses- can undergo a stable genetic relationship within the host (but can also kill cells through lytic cycle)
Lysogeny- state where most virus genes are not expressed and virus genome (prophage) is replicated in synchrony with host chromosome
Lysogen- a bacterium containing a prophage
Slide 38 and 39

21
Q

What are the characteristics of animal virus infections?

A

Entire virion enters cell, unlike in prokaryotes
Eukaryotic cells contain a nucleus which is the site of replication for most animal viruses
Animal viruses contain all known modes of viral replication
Many more kinds of enveloped animal viruses than bacterial viruses

22
Q

What are the consequences of virus infection in animal cells?

A 
Transformation
Lytic infections
Persistent infections
Latent infections
Slide 42 look at!!
23
Q

What are the 6 steps to an influenza virus infecting epithelial cells? (Animal virus infection)

A
  1. Attachment- influenza becomes attached to epithelial cell
  2. Penetration- cell engulfs virus by endocytosis
  3. Uncoating- viral contents are released
  4. Biosynthesis- viral RNA enters the nucleus where it is replicated by the viral RNA polymerase
  5. Assembly- new phage particles are assembled
  6. Release- new viral particles are made and released into extracellular fluid, the cell continues to make new virus
    Slide 43 and 45 pictures
24
Q

What are the 5 steps in the replication of a retrovirus?

A
  1. Entry and uncoating of the retrovirus
  2. Reverse transcriptase activity (2 steps)
  3. Viral DNA enters nucleus and integrated into the host genome
  4. Transcription by host RNA polymerase forms viral mRNA and genome copies
  5. Translation of mRNA forms viral proteins; new nucleocapsids assembled and released by budding
    Slide 46

BMSC 210 (17 decks)

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