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Virology > Structure and Chemical Composition > Flashcards

Structure and Chemical Composition Flashcards

1
Q

What are the two smallest viruses?

A

porcine circovirus type I (17nm diameter) and parvovirus (18nm diameter)

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2
Q

What are the two largest viruses?

A

pandoravirus (400 nm diameter) and poxvirus (200 nm diameter and 300 nm length)

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3
Q

What is pleomorphism?

A

ability of a virus to alter shape or size

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4
Q

Which virus is bullet-shaped?

A

Rabies

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5
Q

Which virus is brick shaped?

A

poxvirus

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6
Q

Which virus is rod-shaped?

A

tobacco mosaic

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7
Q

Which virus is filament-shaped?

A

Ebola

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8
Q

Which virus is spherical?

A

rotavirus

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9
Q

electron microscopy

A
  • need staining -> negative staining with electron dense material (uranyl acetate or phosphotungstate)
  • resolution 50-75 angstroms
  • detailed structural interpretation not always possible
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10
Q

cryo-electron microscopy

A
  • can observe specimens in native environment
  • doesn’t require fixing or staining
  • -180C for liquid nitrogen, -269 for He
  • resolution 3.3-20 angstroms
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11
Q

X-ray crystallography

A
  • virus diffracts x-rays which are detected by a computer to produce an electron density map
  • map used to create a protein model which is used to reconstruct the virus structure
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12
Q

What is a capsid

A

protein shell of a virus that encases/envelops the viral nucleic acid or genome

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13
Q

What is a capsid made of ?

A

capsomeres held together by non-covalent bonds

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14
Q

How many capsids do viruses have?

A

most have one, but reoviruses have a double layered capsid

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15
Q

What is a capsomere?

A

basic subunit protein in the capsid of a virus

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16
Q

What is a nucleocapsid?

A

capsid + virus nucleic acid (DNA or RNA)

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17
Q

helical symmetry

A

capsomeres and nucleic acid are wound together to form helical or spiral tube; incomplete virions cannot form

  • in all animal viruses, helical nucleocapsid is enclosed within a lipoprotein envelope
  • naked helical nucleocapsids common among plant viruses (e.g. tobacco mosaic)
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18
Q

How many corners, facets and edges does an icosahedron have?

A

12 corners
20 facets
30 edges

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19
Q

How many pentons and hexons are present in an icosahedral capsid?

A 
always 12 pentons
# hexons varies with virus group
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20
Q

Triangulation number

A

describes the relation between the number of pentagons and hexagons of the icosahedron; the larger the T number the more hexagons are present relative to pentagons

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21
Q

T number formula

A

T = (h^2) + (h)(k) + (k^2)

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22
Q

What is the simplest icosadedron?

A

parvovirus, T = 1

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23
Q

Reoviridae capsid symmetry

A

outer: T = 13
inner: T = 2

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24
Q

complex symmetry

A

virions are composed of several parts, each with separate shapes and symmetries (e.g. pox viruses)

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25
Q

functions of viral capsid

A
  • responsible for the structural symmetry of the virus particle
  • encases and protects the viral nucleic acid from enzymes, chemicals and physical conditions
  • attachment of virus to specific receptors on susceptible host cells
  • interaction with host cell membranes to form the envelope
  • uncoating of the genome in host cell
  • transport of viral genome to appropriate site
  • facilitates specific recognition and packaging of nucleic acid genome
  • contains antigenic sites that determine antigenicity of virus
26
Q

What makes up an envelope?

A

lipid bilayer with embedded proteins

27
Q

What is the function of an envelope?

A

facilitates virus entry into host cells and may also help the virus to adapt fast and evade the host immune system; cause persistent infections

28
Q

How is the envelope acquired?

A

budding of viral nucleocapsid through a cellular membrane, such as cytoplasmic membrane, golgi membrane or nucleus membrane; budding only occurs at sites where virus specific proteins have been inserted into host cell membrane

29
Q

What are the 2 kinds of viral proteins found in the envelope?

A
  1. glycoprotein

2. matrix protein

30
Q

Which viral proteins are seen as spikes on the virus surface?

A

glycoproteins (transmembrane)

31
Q

external glycoprotein

A

anchored in envelope by a single transmembrane domain and short internal tail; usually major antigens of the virus and involved in functions such as hemagglutination, receptor binding, antigenicity, and membrane fusion

32
Q

channel proteins

A

type of glycoprotein which are mostly hydrophobic and form protein lined channels through envelope; alters permeability of membrane; important in modifying the internal environment of the virus

33
Q

What are 2 examples of external glycoproteins in Influenza virus?

A
  1. Hemagglutinin (HA): binding, fusion, antigenic, hemagglutination
  2. Neuraminidase (NP): release progeny virus from host cell, antigenic
34
Q

Are fusion proteins in HIV and measles pH dependent or pH independent?

A

pH independent

35
Q

Are fusion proteins such as HA in influenza virus pH dependent or pH independent?

A

pH dependent (acidic)

36
Q

virus envelope matrix protein

A
  • link internal nucleocapsid to lipid membrane envelope
  • allow stabilization of lipid envelope
  • recognition site of nucleocapsid at plasma membrane and mediates encapsidation of RNA-nucleoprotein cores into the membrane envelope
37
Q

3 ways viral proteins can interact with viral envelope proteins

A
  1. direct
  2. via matrix protein
  3. via multiprotein layer
38
Q

T/F the lipid bilayer of envelope is sensitive to desiccation, heat, and alteration of pH

A

true

39
Q

3 lipid solvents that can inactivate enveloped viruses:

A
  1. ether
  2. chloroform
  3. sodium deoxycholate, detergents etc.
40
Q

T/F enveloped viruses are difficult to sterilize and can survive for longer periods in environment

A

F: enveloped viruses are easy to sterilize and cannot survive for longer periods in the environment when compared to non-enveloped viruses

41
Q

positive sense viral RNA

A

similar to mRNA and can be immediately translated by host cell

42
Q

negative sense viral RNA

A

complementary to mRNA and must be converted to positive sense RNA by an RNA polymerase before translation

43
Q

monopartite

A

non-segmented genome

44
Q

multipartite

A

segmented genome

45
Q

outcomes of antigenic drift

A
  • most cases minor changes
  • virus may become resistant to antiviral drugs
  • may cause change in antigenicity -> detrimental effect on efficacy of vaccines
46
Q

recombination

A

exchange of nucleotide sequences between different, but closely related, viruses during replication

47
Q

reassortment

A

*most important mechanism for high genetic diversity in viruses with segmented genome

48
Q

lysins

A

hydrolytic enzymes produced by bacteriophages to cleave the host’s cell wall

49
Q

retroviral integrase (IN)

A

enzyme produced by a retrovirus (such as HIV) that enables its genetic material to be integrated into the DNA of the infected cell

50
Q

reverse transcriptase (RT)

A

enzyme used to generate complementary DNA (cDNA) from a RNA template

51
Q

nucleic acid polymerases

A

viral genome replication

52
Q

neuraminidases

A

enzymes that cleave glycosidic bonds; allows released of viruses from host cell

53
Q

structural proteins

A

form the viral capsid; such as VP7 and VP4 proteins of rotaviruses

54
Q

viral nonstructural proteins

A

encoded by viral genome and are produced in the organisms they infect but not packaged into virus particles; may play roles within infected cell during virus replication or act in regulation of virus replication or virus assembly

55
Q

regulatory proteins

A

play indirect roles in the biological processes and activities of viruses

56
Q

defective virions

A

virus that can’t replicate because it lacks a full complement/copy of viral genes; result from mutations or errors in the production or assembly of virions

57
Q

Replication of defective virions occurs only in mixed infections with ____.

A

a helper virus -> supplement genetic deficiency and make defective viruses replicate progeny virions when they simultaneously infect host cell with defective viruses

58
Q

defective interfering particle (DIP)

A

when defective viruses can’t replicate but can interfere with other congeneric mature virion entering the cells

59
Q

pseudovirion

A

contains non-viral genome within the viral capsid; look like ordinary viral particles under electron microscope but don’t replicate
- can be used to inject foreign nucleic acid into a cell, such as delivery of DNA vaccines

60
Q

pseudotypes

A

when related viruses infect the same cell, the genome of one virus may be enclosed in the heterologous capsid of the second virus

Virology (16 decks)

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