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RUSVM Virology Summer 2017 > Structure and Chemical composition of viruses > Flashcards

Structure and Chemical composition of viruses Flashcards

1
Q

What is the smallest virus?

A

Porcine circovirus type 1

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2
Q

What is the largest virus of animals, humans and birds?

A

Poxvirus (200nm diameter and 300 nm in length)

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3
Q

Pleomorphism

A

The ability of some viruses to alter their shape or size

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4
Q

What shape is Ebolavirus?

A

Filament- shaped

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5
Q

What virus is Filament- shaped?

A

Ebolavirus

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6
Q

What shape is Rabies virus?

A

Bullet-shaped

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7
Q

What virus is bullet shaped?

A

Rabies virus

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8
Q

What shape is a bacteriophage?

A

Tadpole- shaped

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9
Q

What virus is tadpole- shaped?

A

bacteriophage

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10
Q

What shape is Tobacco Mosaic Virus?

A

Rod- shaped

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11
Q

What virus is rod- shaped?

A

Tobacco Mosaic Virus

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12
Q

What shape is poxvirus?

A

Brick- shaped

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13
Q

What virus is brick shaped?

A

Poxvirus

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14
Q

What shape is Rotavirus?

A

Spherical

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15
Q

What virus is spherical in shape?

A

Rotavirus

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16
Q

What are the common methods used to determine morphology?

there are 4

A
  1. Electron Microscopy (EM)
  2. Cryo- Electron Microscopy (Cryo- EM)
  3. X-ray Crystallographic Method
  4. Nuclear Magnetic Resonance (NMR)
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17
Q

Capsid

A

The protein shell of a virus that encases/ ENVELOPES the VIRAL nucleic acid or GENOME.

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18
Q

What is the capsid made up of?

A

Capsomeres, held together by NON- covalent bonds.

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19
Q

Capsomere

A

the basic unit protein in the capsid of a virus

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20
Q

How many capsids do MOST viruses have? Is there an exception to the rule?

A

Most viruses have ONE CAPSID!

EXCEPT: REOVIRUSES: which have a double layered capsid.

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21
Q

Nucleocapsid = _______ + _________

A

Nucleocapsid = Capsid + Viral Nucleic Acid (DNA or RNA) / Genome

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22
Q

What 4 components make up a virus?

A
  1. DNA or RNA genes
  2. Capsid
  3. Envelope, a bubble of fat (note: not all viruses have an envelope)
  4. Molecules of protein
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23
Q

Helical Symmetry

A

Nucleocapsids with helical symmetry have capsomeres and nucleic acid wound together to form a helical or spiral tube.

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24
Q

In all animal viruses, the ___A.____ nucleocapsid is enclosed within a _____B._______ envelope.

A

A. Helical

B. Lipoprotein

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25
Q

Naked helical nucleocapsids are common among what type of viruses?

A

Plant viruses! (example: Tobacco Mosaic Virus)

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26
Q

Tobacco Mosaic Virus ( a plant virus) has what type of nucleocapsid?

A

Naked helical nucleocapsid

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27
Q

What types of capsomeres are present in the Icosahedral/ Cubic capsid?

A
  1. Pentagonal capsomers, at the vertices (Pentons)

2. Hexagonal capsomers, making up the facets (Hexons)

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28
Q

Triangulation Number (T- number)

A

Describes the relationship between the number of pentagons and hexagons of the icosahedron.

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29
Q

What is the formula for the Triangulation number?

A

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

h and k are the distances between the successive pentagons on the virus surface for each axis.

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30
Q

There are always 12 hexons, but the number of pentons varies with the virus group. - True/ False

A

FALSE!!!

There are always 12 PENTONS, but the number of HEXONS varies with the virus group.

31
Q

T/F: Naked Icosahedral or Enveloped Icosahedral viruses are possible

32
Q

What is the simplest icosahedron?

A

Parvovirus! (the capsid consists of 60 copies of CP protein)

33
Q

What virus has an outer capsid that has a T= 13 icosahedral symmetry, with the inner capsid a T=2 icosahedral symmetry?

A

Reoviridae!
(It has two Triangulation numbers because Reoviruses have a double layered capsid – they are the exception to the rule that most viruses have one capsid)

34
Q

Virions are composed of several parts, each with separate ___A.___ and ____B.____.

A

A. Shapes
B. Symmetries
(example Pox Virus)

35
Q

Functions of the viral capsid

A
  1. Responsible for STRUCTURAL SYMMETRY of the virus particle
  2. ENCASES AND PROTECTS the VIRAL NUCLEIC ACID from enzyme (nucleases), chemicals and physical conditions (pH and temperature)
  3. Receptor attachement proteins on viral capsid FACILITATE the ATTACHMENT OF the VIRUS TO SPECIFIC RECEPTORS ON the susceptible HOST CELL
  4. INTERACTION with HOST CELL membranes to FORM the ENVELOPE
  5. UNCOATING the GENOME in the host cell
  6. TRANSPORT of the viral GENOME to the appropriate site (may dump the genome into the cytoplasm [most +ssRNA viruses] or serve as the core of replication– example Reovirus and Retrovirusains)
  7. Facilitates specific RECOGNITION and PACKAGING of the nucleic acid GENOME
  8. Capsid contains ANTIGENIC SITES which determine the ANTIGENICITY of the virus.
36
Q

T/F: Many viruses have an envelope.

37
Q

What is the envelope of a virus usually made up of?

A

A lipid bilayer with embedded proteins

38
Q

What does the envelope of a virus facilitate?

A

Entry into host cells and may also help the virus to adapt fast and evade the host immune system

39
Q

What type of infections can enveloped viruses cause?

A

Persistent infections

40
Q

How is the envelope acquired?

A

By budding of viral nucleocapsid through a cellular membrane, such as cytoplasmic membrane, golgi membrane, or nucleus membrane.

41
Q

What are the two kinds of viral proteins primarily found in the envelope?

A
  1. Glycoprotein (aids in fusion)

2. Matrix Protein

42
Q

What does glycoprotein aid in?

43
Q

What virus has complex capsid symmetry?

44
Q

What are the two types of glycoproteins in a virus envelope?

A
  1. External glycoprotein

2. Channel proteins

45
Q

External Glycoprotein

A

Proteins that are usually the major ANTIGENS OF THE VIRUS and are involved in functions such as hemagglutination, receptor binding, antigenicity, and membrane fusion

46
Q

Channel Protein

A

Mostly hydrophobic proteins that form a protein lined channel through the envelope. This proteins alters permeability of the membrane (ex. Ion channel). Such proteins are IMPORTANT IN MODIFYING the INTERNAL ENVIRONMENT OF the VIRUS.

47
Q

Matrix Protein

A
  • These proteins LINK THE INTERNAL NUCLEOCAPSID TO the LIPID MEMBRANE ENVELOPE
  • play a crucial role in VIRUS ASSEMBLY
  • Allow STABILIZATION of the lipid ENVELOPE
  • Serves as the RECOGNITION SITE OF NUCLEOCAPSID AT THE PLAMSA MEMBRANE and mediates the encapsidation of the RNA- nucleoprotein cores into the membrane envelope
48
Q

Where is the lipid bi-layer of virus envelope acquired from?

A

cellular membrane of host cell, such as cytoplasmic membrane, nuclear membrane, ER membrane, etc.

49
Q

What type of environment(s) is the lipid bi-layer in virus envelope maintained?

A

Aqueous or moist environments

the lipid envelope is sensitive to desiccation, heat, and alteration of pH

50
Q

How can envelope viruses be inactivated?

A

by the dissolution of lipid membrane with lipid solvents such as:

  • Ether
  • Chloroform
  • Sodium deoxycholate, Detergents, etc.
51
Q

Which virus is easier to sterilize, enveloped viruses or Non- enveloped viruses?

A

Enveloped Viruses

52
Q

T/F: Envelope viruses can NOT survive for longer periods in the environment than non- enveloped viruses.

A

True!
(remember that enveloped viruses are maintained only in aqueous or moist environments and are sensitive to desiccation, heat, and alteration of pH)

53
Q

Viral DNA

A

Can be linear or circular

54
Q

RNA Genome can be

A

Monopartite (Non- Segmented)
or
Multipartite (Segmented)

55
Q

Monopartite

A

Non- segmented RNA genome

56
Q

Multipartite

A

Segmented RNA genome

57
Q

Virus Nucleic Acids can be composed of…

A

DNA- dsDNA or ssDNA
or
RNA- dsRNA or ssRNA
(note: ds= double stranded; ss= single stranded)

58
Q

(+) Sense RNA Virus

A

Infectious Genome

Postive- sense viral RNA is similar to mRNA and thus can be immediately translated by the host cell

59
Q

(-) Sense RNA Virus

A

Noninfectious Genome
(Negative sense- viral RNA is complementary to mRNA and thus must be converted to positive- sense RNA by an RNA polymerase before translation)

60
Q

Mechanisms of Genetic Diversity of Viruses

A
  1. Antigenic Drift (mutations)

2. Antigenic Shift

61
Q

Antigenic Drift

A

MUTATIONS! Gives Genetic diversity to a virus

  • most cases are minor changes
  • Virus may become resistant to antiviral drugs
  • May cause change in antigenicity -> detrimental effect on efficacy of vaccine
  • POINT MUTATIONS (Silent, Nonsense, Missense)
62
Q

What are the 3 point mutations?

A
  1. Silent
  2. Nonsense
  3. Missense
    (they are apart of antigenic drift)
63
Q

Antigenic Shift is composed of what 2 mechanisms of genetic diversity?

A
  1. Recombination

2. Reassortment

64
Q

Recombination

A

Intramolecular recombination involves the exchange of nucleotide sequences between different, but usually closely related, viruses during replication. (Part of Antigenic Shift)

65
Q

Reassortment

A

MOST IMPORTANT MECHANISMS for high genetic diversity IN VIRUSES with SEGMENTED GENOME. (part of Antigenic Shift)

66
Q

What are the important viral enzymes critical to infection?

A
  1. Retroviral Integrase (IN)
  2. Reverse Transcriptase (RT)
  3. Nucleic Acid Polymerases
67
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

68
Q

Reverse Transcriptase (RT)

A

Enzyme used to generate complimentary DNA (cDNA) from a RNA template

69
Q

Nucleic Acid Polymerases

A

Viral genome replication

70
Q

Viral Nonstructural proteins

A

proteins may play roles within the infected cell during virus replication or act in regulation of virus replication or virus assembly

71
Q

Incomplete Virions

A

Virion without nucleic acid (empty capsid)

72
Q

Defective Virions

A

A virus that cannot replicate because it lacks a full complement/ copy of viral genes. Defective viral particles result from mutations or errors in the production or assembly of virions.

73
Q

Pseudovirion

A

Contains non-viral genome within the viral capsid, such as host nucleic acid instead of viral nucleic acid.

74
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.

RUSVM Virology Summer 2017 (23 decks)

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