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+ MICB 202 Final > *** Virology Chapter 1: General Features of Virus Structure > Flashcards

*** Virology Chapter 1: General Features of Virus Structure Flashcards

1
Q

What is a virus?

A

chemical complexes of RNA or DNA protected by protein

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2
Q

Are viruses living or non-living?

A

non-living

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3
Q

Why are viruses obligate intracellular parasites?

A

require host cells to reproduce

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4
Q

What does each type of virus infect?

A

a specific unicellular species OR cell type in a multicellular species

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5
Q

Are viruses cells? Why?

A

no

cannot synthesize their own ATP or amino acids or nucleotides
- lack abilities to extract energy from molecules to build nucleic acids
and proteins
- lack “instructions” to make nucleotides and amino acids
- lack ribosomes

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6
Q

What are the 2 possible states viruses can be in?

A

extracellular state

intracellular state

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7
Q

What is a virus in extracellular state?

A

inert particle (protein, nucleic acid, maybe lipid)

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8
Q

What is a virus in intracellular state?

A

replicating nucleic acids (gene expression, viral proteins)

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9
Q

Viruses vs. Cells

What is the hereditary material?

A

virus: DNA or RNA, can be single or double-stranded
cells: DNA, always double-stranded

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10
Q

Viruses vs. Cells

Is there a plasma membrane?

A

virus: no, but may have an envelope
cell: yes

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11
Q

Viruses vs. Cells

Can it carry out transcription independently?

A

virus: no – requires ATP and nucleotides from host cell
cell: yes

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12
Q

Viruses vs. Cells

Can it carry out translation independently?

A

virus: no
cell: yes

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13
Q

Viruses vs. Cells

What are the metabolic capabiities?

A

virus: none (not detectable)
cell: extensive – ATP synthesis, oxidation of reduced C, amino acid and nucleotide biosynthesis, etc.

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14
Q

What percentage of your genome has its origins in virus sequences?

A

~ 50%

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15
Q

What is the central dogma of molecular biology?

A

flow of genetic information within a biological system – applies to all living cells, and viruses to (sometimes with a twist)

DNA → RNA → protein
RNA → RNA → protein
RNA → DNA → RNA → protein

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16
Q

What are the 3 types of virus structures?

A

naked
enveloped
complex capsids

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17
Q

Viruses are a diverse group of infectious agents. What are the types of genetic material viruses can be made of?

A

ssDNA
dsDNA
ssRNA
dsRNA

(can be linear or circular DNA or RNA)

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18
Q

What type of host cell is infected by viruses?

A

species specific, and cell/tissue specific

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19
Q

Can viruses infect more than one cell type, and/or more than one species?

A

yes

ie. infects only humans: poliovirus, HIV, smallpox
ie. infects humans and other animals: influenza, rabies, measles, coronavirus, ebola

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20
Q

What are the replication strategies of viruses?

A
  • where the genome is replicated in the cell
  • replication cycle (lytic, persistent, latent)
  • on or more ‘rounds’ of mRNA expression
  • etc.
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21
Q

What are the 2 general categories of virus structure?

A

enveloped and non-enveloped (naked)

22
Q

What is the genome of a naked virus enclosed by?

A

only the capsid (protein shell – aka nucleocapsid)

23
Q

What is a capsid made of?

A

capsomeres (multiple copies of protein subunits) – it could be made from one type of protein or several different proteins

24
Q

What do capsomeres do?

A

might bind directly to a structure on a host cell, or there may be attachment proteins that project out of the capsid (ie. spikes)

25
Q

Where is the gene that encodes the protein structure that is called the
capsomere?

A

in virus’ genome

26
Q

What is the structure of an enveloped virus?

A
  • capsid
  • lipid bilayer that surrounds capsid (can be derived from plasma membrane or any other membrane structure)
  • some have a matrix layer of protein just below the envelope
27
Q

What does the envelope envelope?

A

glycoproteins encoded by the virus (proteins modified with carbohydrate) and embedded in the lipid bilayer, that are required for attachment to the host cell

28
Q

Where would the envelope structure come from?

A

stolen from host cell

29
Q

Why do some viruses have envelopes, and others don’t?

A

related to viruses replication cycle

enveloped:
- virus buds through the membrane and acquires the envelope without killing host cell immediately
- virus replication occurs for prolonged periods of times (as long as years)

naked:
- cell lyses, and all progeny are released at once (cell is dead)

30
Q

Which virus would be more fragile in the environment? For example, which type of virus would likely be infectious after 1 hour on a countertop surface?

A

enveloped virus

31
Q

What is the ‘complex’ structure that some viruses have?

A

possesses a capsid that is not helical or icosahedral and may have other structures like a protein tail or complex outer wall.

32
Q

Why study viruses?

A
  • some viruses do cause disease – humans, domesticated animals (pets and livestock), wild animals, and crops
  • many societal impacts
  • if one understands the virus that causes a specific disease, one can develop
    protocols to limit the spread and/or prevent infection altogether
33
Q

What are cool enzymes? What do they do? What are some examples

A

reverse transcriptase and RNase H

enables pharmaceutical companies to manufacture human products in bacteria or yeast cells

insulin, Factor VIII, Factor IX, human growth hormone, erythropoietin,
interferons, interleukins, parathyroid hormone and others

34
Q

What is anti-microbial therapy?

A

bacteriophages to treat patients with bacterial infections (topical ointments, enemas, mouthwashes) and also used as antiseptics and disinfectants

35
Q

What is gene therapy?

A

use viruses as a delivery system to deliver a wild type copy of a gene to a cell type that is carrying a mutated copy of the gene

36
Q

How are viruses used in treatment of cancer?

A
  • some cause cancer
  • some can be genetically modified to be used as anti-cancer agents that can replicate in cancer cells (ie. cancer cells are permissive) but not healthy cells (ie. healthy cells are not permissive)
37
Q

Where do viruses that infect humans come from?

A

not clear – many hypotheses…escaped genetic elements?

problem: no fossil record.

difficult to track: high mutation rate, some integrate into host genome, some do genetic re-assortment

38
Q

Where do ‘new (strains)’ viruses evolve from?

A

pre-existing viruses

39
Q

What might describe some method(s) that viruses use to “jump” to new hosts?

A
  • virus is excreted by an animal in its urine/feces – the urine/feces
    contaminates a food source or water supply
  • virus is excreted by an animal in its urine/feces onto a dirt floor – the virus
    is inhaled by the new host when it is aerosolized
  • infected animal is slaughtered – the butcher cuts their hand with a knife
    and the animal’s blood enters into the wound
  • infected animal dies or is slaughtered – the resulting meat is consumed
    by the new host without cooking
40
Q

What are the two general pathways of virus evolution?

A
  • co-evolution with host

- infection of multiple host species

41
Q

What is an advantage, disadvantage, and example of co-evolution with host (pathway of virus evolution)?

A
  • advantage for virus: prosperous host = prosperous virus
  • disadvantage for virus: host becomes extinct, so does virus
  • example: smallpox (in humans)
42
Q

What is an advantage, disadvantage, and example of infection of multiple of host species (pathway of virus evolution)?

A
  • advantage: if one host species is compromised, virus can replicate in another
  • disadvantage: cannot optimize for any one situation
  • example: influenza, rabies
43
Q

Fitness in Co-evolution

What happens if a mutation is not good for the virus?

A

it might lose its ability to infect a cell, which is needed to produce more virus

44
Q

Fitness in Co-evolution

What happens if a mutation is neutral to the virus?

A

no obvious effect on the virus

45
Q

Fitness in Co-evolution

What happens if a mutation is beneficial to the virus?

A

might gain an ability to infect a new host, or infects its host more efficiently (higher virulence)

46
Q

What is the downside to highly virulent viruses?

A
  • will kill the host too soon

- if it is too exposed, the host’s immune system will kill it

47
Q

What type of relationship do viruses and hosts tend to co-evolve toward?

A

symbiotic

48
Q

What are coronaviruses?

A

enveloped virus with a helical capsid, and a single-stranded RNA genome

49
Q

What is the length of the coronavirus genome?

A

between 27-32 kb (largest genome of RNA viruses)

50
Q

What are the 3 virus proteins?

A
  • spike (S) protein: binding and entry
  • membrane (M) protein: assembly, shape
  • envelope (E) protein: ? assembly

+ MICB 202 Final (20 decks)

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