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Virology > Basics > Flashcards

Basics Flashcards

1
Q

Characteristics virus (vs bacteria)

A

Intracellular parasite, needs cell to replicate.

Others: size, cellular machinery, plasma membrane.

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2
Q

Virus genome

A

Nucleic acid.

Variable size, haploid (except Retroviruses), DNA/RNA, +/-, ss/ds, linear/circular segmented

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3
Q

Capsid

A

Protects genome.
Helical/icosahedral/complex shape.
For naked (no envelope) viruses relevant for entry (eg Papilloma virus)

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4
Q

Envelope/membrane

A

Optional. Lipid bilayer derived from host cell > contains cellular and viral proteins (incl glycoproteins mediating binding and host cell entry)

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5
Q

Def. virion, surface protein, nucleocapsid, structural proteins.

A

Virion = virus particle

Surface proteins = glyco-/envelope/membrane protein

Neucleocapsid = capsid + genome (inside particle)

Strucutral proteins = viral proteins present within virions
(non-str.: expressed in infected cell, not contributing to particle structure

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6
Q

Virus replication

A
  1. Attachment and entry
  2. Uncoating (>release of genome)
  3. Gene expression and genome replication
  4. Assembly and release (from infected cel)
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7
Q

Classification

A

Viruses can be classified according to their components (classical approach).

Alternative approach: Baltimore system (focus on generation of mRNA).

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8
Q

Determinants of viral sensitivity to disinfectants

A

Presence of envelope is associated with increased sensitivity to disinfectants

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9
Q

Under which conditions will bacteria/virus replicate?

A

Virus: cells in culture
Bacteria: LB medium

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10
Q

2 Types of transmission

A
  1. Horizontal (between members of same species, not in parent-child relationship)
  2. Vertical (transmission from mother to child)
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11
Q

Types of horizontal transmission + ex

A 
Parenteral (blood) - eg HIV
Fecal oral (feces) - HepA
Droplets - Influenza
Vectors - FSME
Organ transplantation - CMV
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12
Q

Types of vertical transmission

A

In utero
Intrapartum (perinatal)
Breast milk (postnatal)

eg HIV

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13
Q

Portals of entry

A

Mucosal tissue
Skin
Blood

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14
Q

Acute vs persistent infection

A

Acute: Immune system clears virus (or host dies) (eg Influenza)

Persistent: immune evasion, virus replication continues despite immune response (eg HIV)

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15
Q

Persistent vs latent

A

Persistent: viral replication can be detected at each time point (HIV)

Latent: phases without viral replication and phases of reactivation of viral replication (Herpes)

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16
Q

Primary vs permanent cell culture

A

Primary: generated directly from tissue, contain, several types, divide about 20 times

Permanent: cells are immortalized, divide continuously, generate from primary cultures by treatment with mutagenic agent/tumor viruses, adherent or suspension culture

17
Q

Cytophathic effect (CPE), ex

A

Changes in cell morphology, to some degree virus-specific.
Smaller nucleus > Picorna
Syncytia > Corona
Rounding/detachment > Rhabdo

Neutralizing ab can block CPE development.

18
Q

Plaque test

A
  1. seed adherent cells
  2. inoculate cell monolayers with diff dilution of viruses
  3. remove excess viruses, cover cells with agar
  4. Dye for visualization

Each hole (plaque) from one infectious unit (PFU)

19
Q

PFU, MOI

A

PFU: plaque-forming units (PFU/ml)

MOI: multiplicity of infection (PFU/cell)

20
Q

Diagnostics - options

A

Detection of viral material: PCR, ELISA, EM

Detection of ab: ELISA; Complement binding reaction, neutraliztation test, Western Blot

21
Q

EM characteristics

A

Rapidly detect infectious agents. High particle conc required. Particle visualization with heavy metals

22
Q

Neutralisation test

A

Neutralising ab bind GP > prevent entry.

Plaque assay: at which dilution is plasma able to prevent appearance of plaques?

23
Q

Entry of non-enveloped viruses

A

Pore formation:

Receptor binding > conformational changes in coat protein, endocytosis > pore formation > genome release

(eg Polio)

24
Q

Entry of enveloped viruses

A

Membrane fusion. Mediated by GPs.
Diff classes:
1 (Retrov.), 2 (Alphav.) 3 (Rhabdov.)

Porcesses: Priming, triggering

25
Q

Priming

A

Membrane fusion proteins (GPs) must be primed: sythesis as inactive precursors > cleavage by host cell protease

eg Inluenza hemagglutinin

prevents premature triggering

26
Q

Triggers of membrane fusion - ex

A

Receptor binding triggers membrane fusion (eg Avian retroviruses)

Internalization into endosome > low pH triggers fusion (eg Influenza)

27
Q

Replication in DNA viruses

A 
Transcription and replication interconnected.
Early phase (E): enzymes for genome replication, negative autoregulation, synthesis of transactivators for L phase.
Late phase (L): produciton of structural proteins

Replicaiton requires on origin and priming.

28
Q

Modes of DNA replication initiation

A 
RNA primin (Polyomav.)
Protein priming (Adenov.)
Hairpin priming (Parvov.)
29
Q

RNA viruses - initiation of translation

A

Cap-dependent
Assembly of 40S ribosome + initiation factors
Scan for AUG (start codon)

30
Q

Picronavirus RNA

A

Not capped. Ribosomes bind via IRES (internal ribosomal entry sites at 5’UTR).

31
Q

Coding strategy of Picornaviridae

A

Encode for one bif precusor (poly)protein > processed by viral proteases

32
Q

Rhabdoviridae transcription

A

RdRP (pol) binds to terminal leader sequence > transcription starts at intergenic regions > mRNA expression levels correlate with position in genome

33
Q

Packaging of nucleic acids

A

Simple: condensation of protein shell around nucleic acid (+RNA v.)

Complex: preformatino of capsid eg via scaffold then packaging of nucleic acid (eg DNA v.)

Packaging signals required.

34
Q

Virus release strategies

A
  1. Cell lysis (naked viruses)

2. Budding (enveloped viruses

35
Q

Sites of budding

A

Viruses can use different cellular compartments: cell membrane, rER, Golgi, intermediate compartment

36
Q

ESCRT proteins

A

Facilitate membrane fission and particle release.

37
Q

Maturation

A

Transit of precursor proteins in their functional forms by proteolytic processing.
Required for infectivity.

Virology (7 decks)

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