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Microbiology PMY 3 > Introduction To Viruses AMG- DLA > Flashcards

Introduction To Viruses AMG- DLA Flashcards

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1
Q

Viral genomes can be:

A

Viral genomes can be:

Single stranded(ss), double stranded(ds), linear, circular, segmented, haploid or diploid

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2
Q

How do viruses appear in light microscopy?

A

“Invisible” by light microscopy with sizes ranging from 20-400nm

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3
Q

What is a virion?

A

A virion is a complete infectious form of virus outside the host cell (extracellular)

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4
Q

What do viruses infect?

A

Viruses infect any living organism e.g., vertebrates, invertebrates, plants, bacteria and fungi

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5
Q

What do viruses consist of?

A

Viruses are non-cellular organisms that consist of either DNA or RNA that is surrounded by a protein coat

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6
Q

What kind of parasites are viruses?

A

Obligate “intracellular parasites” that require a host cell for replication

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7
Q

How are virions formed?

A

Individual virion components self-assemble into a virion

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8
Q

Describe the structure of viruses

A
  • Most viruses are structurally simple, however, some viruses have more complex structure
  • The basic biophysical and biochemical rules of the viral structure and assembly are same for all viruses
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9
Q

What are the viral structure components?

A
  • Genome
  • Capsomere
  • Nucleocapsid
  • Virus specific glycoproteins
  • Envelope
    • tegument
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10
Q

What is the viral capsomere?

A

Viral (protein) subunits that assemble into caspid

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11
Q

What is the viral genome composed of?

A

Either DNA or RNA

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12
Q

What is the nucleocaspid?

A

Genome assembled into the caspid

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13
Q

Differentiate between the viral tegument and viral envelope

A

Viral envelope- outer layer that originates from the host membranes and covers the caspid to maintain aqueous.

Viral tegument- a cluster of proteins that line the space between the envelope and nucleocaspid

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14
Q

What is the structure and the main function of the virus caspid?

A

Structure: consists of single or several different subunits(capsomeres) that have variable size, have identifiable domains and symmetry

Held together by non-covalent, reversible hydrophobic or hydrogen bonds

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15
Q

What are the functions of the viral capsid?

A

The viral capsid serves to protect the nucleic acid and genome

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16
Q

What is the purpose of the viral capsid proteins?

A

Capsid proteins have several functions:

  • define tissue or species specific transmission by interaction with host receptors to facilitate the host cell entry
  • interact with the viral nucleic acid for packaging/assembling the virus.
  • Assist in viral and/or host gene regulation
  • Evade/block host immune system, and other functions
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17
Q

What are the forms of virus nucleocapsid morphology?

A

Three generals forms of nucleocapsid morphology:

  • icosahedral(roughly spherical)
  • helical
  • complex (nonsymmetrical)
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18
Q

Describe the axes of symmetry in the Icosahedral Capsid and what causes it

A

The protomers assemble into pentamer

The icosahedral capsid has a complex 5-3-2 axes of symmetry e.g., poliovirus

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19
Q

Describe the formation of Icosahedral Capsid

A
  • Few proteins assemble in a basic protomers
  • The amount of nucleic acid that can be packaged is limited by the size of the particle.

Icosahedral capsid form independently of the genome

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20
Q

How do helical capsid appear?

A

Like rod-like, filamentous structures(May be rigid or flexible depending on the specific virus)

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21
Q

Where do helical capsule form?

A
  • Capsomers bind to the viral genome in a regular fashion

- Hellical capsid are “open-ended “ and form around the genome. No empty helical capsid can form

22
Q

What is common about all hellically shapes animal viruses?

A

All known examples of animal viruses with helical symmetry contain RNA genomes and have flexible nucleocapsid wound into a ball and surrounded by envelope, except: Rhabdoviruses

23
Q

Describe the structure of the complex capsid

A

Bacteriophages or phages (bacterial viruses) exhibit complex symmetry

Head- nucleic acid and protein

Tail and contractive sheath

Tail fibers and tail pins

Base/end plate

24
Q

Describe the capsid structure of a retrovirus

A

Retroviruses possess a distinctive cone-shaped capsid structure.

Retroviruses posses a 3 layer capsid that contains 11 dsRNA segments

25
Q

Give an example of a retrovirus

A

E.g. human immunodeficiency virus (HIV)

26
Q

What is the viral envelope?

A

Viral envelope is a lipoprotein membrane derived from host membrane can be:

  • cell plasma membrane (HIV; most of the enveloped viruses)
  • Nuclear or other internal (endoplasmic reticulum) membranes (herpesvirus) and contains virus specific proteins.
27
Q

How much host proteins are in viral envelopes ?

A

The viral envelope is poor in host call proteins, but rich in virus specific glycoproteins-viral attachment protein (VAP)

28
Q

What is the shape of enveloped viruses?

A

-Enveloped viruses are usually spherical or pleomorphic in shape except rhabdovirus (Rabies, bullet shaped) and poxvirus (smallpox, complex)

29
Q

How are enveloped viruses transmitted?

A

Usually transmitted by secretions, large droplets, blood or sexual contact e.g., measles viruses

30
Q

How many an enveloped virus be inactivated?

A

They are sensitive to inactivation by organic solvents (alcohol, chloroform, ether, etc.) detergents, drying, acid, heat.

31
Q

What is a naked virus?

A

-viral nucleocapsid is naked

32
Q

Describe the difficulty of inactivation to non-enveloped viruses

A

Non-enveloped(naked) viruses are tough and relatively resistant to inactivation by organic solvents (alcohol, chloroform, ether etc.,) detergents, drying, acid and heat

33
Q

Hoe are non-enveloped (naked) viruses usually transmitted?

A

Usually transmitted by fecal /oral route, vomited or small droplets

34
Q

How are non-enveloped viruses released from infected cells?

A

By lysis e.g., poliovirus, adenovirus

35
Q

What are the functions of the Viral Attachment Proteins or peplomers (VAP)?

A

Facilitate host cell entry, e.g., hemaglutinin (HA) on influenza virus which binds erythrocytes, VAP on Epstein-Barr virus(EBV) binds C3d receptor(CR2) on B cells

36
Q

What is the function of viral polymerase?

A

Present within the genome of viruses and involved in transcription and replication of viral genome

37
Q

Where are viral matrix proteins?

A

Matrix proteins is present between the nucleocapsid and envelope

38
Q

What is the function of viral matrix proteins?

A

Stabilize the organization of viral glycoprotein, directs the viral genome to intracellular sites of the viral assembly, facilitate virus assembly and budding

39
Q

How can the viral proteins be divided?

A

Depending on the virus and it’s expression pattern, viral proteins are divided into :

  • immediate early phase proteins
  • early phase proteins
  • late phase proteins
40
Q

What are the characteristics that are involved viral nomenclature?

A
  1. Morphology
  2. Physicochemical properties: thermal stability, detergent stability, ,molecular mass, etc.
  3. Genome: size, type of nucleic acid, strandedness
  4. Proteins:
  5. Lipids: content, character
  6. Carbohydrates: content, character
  7. Genome organization and replication
  8. Antigenic properties: seriological relationships
  9. Biological properties: Host range, mode of transmission, pathogenicity, tissue tropisms, geographic.
41
Q

What factors of morphology play a role in viral nomenclature ?

A

Size, shape, presence of envelope

42
Q

What factors of genome organization and replication play a role in viral nomenclature?

A

Strategy of replication, number and position of open reading frames, transcriptionally and translational strategies, site of virion assembly and release

43
Q

What committee controls viral nomenclature?

A

The international committee on Taxonomy of Viruses(ICTV, 1966) utilizes a universal system for classifying viruses

44
Q

What is included in the viral nomenclature system used by the ICTV ?

A

The system makes use of series of ranked taxons (order/family/ sub-family/genus/ species)

Order
Family(-idae)
Subfamily(-inae)
Genus(-virus)
Species
[isolates, strains]
45
Q

Give the nomenclature process of the Measles disease

A

Order: Mononegavirales

Family: Paramyxoviridae

Subfamily: Paramyxovirinae

Genus: Morbillivirus

Species: Measles virus

46
Q

What is the Baltimore Classification system ?

A

A nomenclature classification system that places viruses into one of seven groups depending on a combination of their nucleic acid (DNA or RNA), strandedness (single-stranded or double-stranded), sense, and method of replication.

Named after David a Baltimore, a Nobel prize-winning biologist, these groups are designated by Roman numerals

47
Q

Give examples of dsDNA viruses

A

E.g., adenoviruses, Herpes viruses, Poxviruses

48
Q

Give an example of dsRNA viruses

A

Reoviruses

49
Q

What are ssDNA viruses, give an example

A

+ve strand or “sense” DNA (e.g. Paroviruses)

50
Q

What are (+ve )ssRNA viruses , give an example

A

(+ve strand or sense) RNA (e.g. Picornaviruses, togaviruses)

51
Q

What are ssRNA-RT viruses? Give an example

A

(+ve strand or sense) RNA with DNA intermediate in life cycle (e.g. Retroviruses)

52
Q

What is the dsDNA-RT viruses? Give an example

A

DNA with RNA intermediate in life cycle (e.g. Hepadnaviruses)

Microbiology PMY 3 (24 decks)

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