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virology > lecture 2 > Flashcards

lecture 2 Flashcards

1
Q

Smallest viruses

A

porcine circovirus type 1

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2
Q

largest viruses

A
  • Poxvirus (200 nm diameter and 300 nm in length)

- in animals, humans, and birds

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3
Q

Pleomorphism

A

ability of virus to alter size or shape

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4
Q

Common methods to determine morphology of virus

A
  • electron microscopy
  • Cryo-Electron Microscopy (Cryo-EM)
  • X-ray crystallography
  • Nuclear Magnetic Resonsonance (NMR)
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5
Q

Capsid

A
  • protein shell of virus that encases/envelopes the viral nucleic acid or genome
  • capsid is made up of capsomeres
  • most viruses have one capsid, except Reoviruses which are double layered
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6
Q

Capsomere

A

basic subunit protein in the capsid of a virus

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7
Q

Nucleocapsid

A

capsid+ viral nucleic acid (DNA or RNA)/ Genome

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8
Q

Capsid symmetry and virus architecture

A
  • helical symmetry

- cubic/icosahedral symmetry

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9
Q

helical symmetry

A
  • in all animal viruses, helical nucleocapsid is enclosed within a Lipoprotein Envelope
  • naked helical nucleocapsids are common among plant viruses (eg. tabacco mosaic virus)
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10
Q

cubic/icosahedral symmetry

A
  • two types of capsomeres present in icosahedral capsid
  • the pentagonal capsomeres at the vertices (pentons) and hexagonal capsomeres at the facets (hexons)
  • there are always 12 pentons, but number of hexons varies by virus group
  • triangulation number
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11
Q

triangulation number (T-number)

A
  • describes the relationship between the number of pentagons and hexagons in icosahedron
  • calculated using the formula: T=h^2+h*k+k^2
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12
Q

true/false: icosahedron may be naked or enveloped

A

true

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13
Q

Parvovirus icosahedral symmetry

A

-T=1, simples, capsid consists of 60 copies of CP protein

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14
Q

Reoviridae icosahedral symmetry

A
  • outer capsid= T=13 symmetry

- inner capsid is T=2 symmetry

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15
Q

Which type of virus we discussed has a capsid with a complex symmetry?

a. Reovirus
b. Herpes virus
c. Pox Virus
D. HIV

A

C. pox virus

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16
Q

functions of the viral capsid

A
  • structural symmetry of virus particle
  • encases and protects viral nucleic acid from enzymes (nucleases), chemical and physical conditions (pH and temp)
  • receptor attachment proteins on viral capsid facilitates attachment of receptors to the susceptible host cells
  • interaction with host cell membranes to form envelope
  • uncoating of genome in host cell
  • transport of viral genome to appropriate site
  • packaging of nucleic acid genome
  • determines antigenicity of the virus
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17
Q

enveloped viruses

A
  • envelope is lipid bilayer with embedded proteins
  • envelope acquired by budding of viral nucleocapsid through cellular membrane such as cytoplasmic membrane, golgi membrane, or nuclear membrane
  • composed of glycoprotein and matrix protein
18
Q

Types of Glycoprotein in Viral Envelope

A
  • external glycoprotein

- channel proteins

19
Q

External glycoprotein

A

usually major antigens of virus, function in hemagglutination, receptor binding, angtigenicity, and membrane fusion

20
Q

channel proteins

A
  • mostly hydrophobic
  • form a protein channel through the envelope
  • alters the permeability of the membrane (ion channel)
  • important in modifying internal environment of the virus
21
Q

Other types of proteins than glycoproteins in the viral envelope

A
  • fusion proteins

- matrix proteins

22
Q

Matrix protein

A
  • provides link between internal nucleocapsid to the lipid membrane envelope
  • crucial role in virus assembly
  • stabilization of lipid envelope
  • recognition site of nucleocapsid at the plasma membrane
  • mediates encapsidation of RNA-nucleoprotein cores into the membrane envelope
23
Q

Lipid bi-layer in virus envelope

A
  • acquired from cell membrane of host cell such as cytoplasmic membrane, nuclear membrane, ER membrane, etc
  • maintained only in aqueous or moist environments, sensitive to dessication, heat, and alteration of pH
  • enveloped viruses can be inactivated by dissolution of lipid membrane with lipid solvents such as: ether, chloroform, sodium deoxycholate, detergents, etc
  • enveloped viruses easier to sterilize than non-enveloped viruses, cannot survive for longer periods in environment
24
Q

Which of the following is not a component of a virus?

A. nucleic acid
B. Capsid
C. Envelope
D. Capsule

A

D. capsule

25
Q

The viral matrix protein is located between the viral nucleic acid (DNA/RNA) and the capsid

A

B. False

26
Q

Mechanisms of genetic diversity of viruses

A
  1. antigenic drift (mutations)
  2. Antigenic shift:
    - -recombinations
    - -reassortment
27
Q

Recombination (antigenic shift)

A

-intramolecular recombination involves the exchange of nucleopeptide sequences between different, but usually closely related, viruses during replication

28
Q

reassortment (antigenic shift)

A

-most important mechanism for genetic diversity in viruses with segmented genome

29
Q

Which of the following is not a mechanism of genetic diversity of viruses?

A. reassortment
B. point mutations
C. recombination
D. conjugation

A

D. conjugation

30
Q

retroviral integrase

A

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

31
Q

reverse transcriptase

A

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

32
Q

nucleic acid polymerases

A

-viral genome replication

33
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

34
Q

nonstructural proteins are seen in extracellular virions

T/F

A

false

35
Q

incomplete virions

A

virion without nucleic acid (empty capsid)

36
Q

defective virions

A
  • virus that can’t 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
37
Q

Psuedovirion

A

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

38
Q

Psuedotypes

A

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

39
Q

An incomplete virion is composed of:

A. only nucleic acid (DNA/RNA)
B. only lipid envelope
C. only capsid
D. lipid envelope and nucleic acid, no capsid

A

C.

40
Q

Which of the following is not a component of a virus?

A. nucleic acid
B. Capsid
C. envelope
D. capsule

A

D. capsule

virology (12 decks)

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