Basics

Question 1

Characteristics virus (vs bacteria)

Answer 1

Intracellular parasite, needs cell to replicate.

Others: size, cellular machinery, plasma membrane.

Question 2

Virus genome

Answer 2

Nucleic acid.

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

Question 3

Capsid

Answer 3

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

Question 4

Envelope/membrane

Answer 4

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

Question 5

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

Answer 5

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

Question 6

Virus replication

Answer 6

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

Question 7

Classification

Answer 7

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

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

Question 8

Determinants of viral sensitivity to disinfectants

Answer 8

Presence of envelope is associated with increased sensitivity to disinfectants

Question 9

Under which conditions will bacteria/virus replicate?

Answer 9

Virus: cells in culture
Bacteria: LB medium

Question 10

2 Types of transmission

Answer 10

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

Question 11

Types of horizontal transmission + ex

Answer 11

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

Question 12

Types of vertical transmission

Answer 12

In utero
Intrapartum (perinatal)
Breast milk (postnatal)

eg HIV

Question 13

Portals of entry

Answer 13

Mucosal tissue
Skin
Blood

Question 14

Acute vs persistent infection

Answer 14

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

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

Question 15

Persistent vs latent

Answer 15

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

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

Question 16

Primary vs permanent cell culture

Answer 16

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

Question 17

Cytophathic effect (CPE), ex

Answer 17

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

Neutralizing ab can block CPE development.

Question 18

Plaque test

Answer 18

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)

Question 19

PFU, MOI

Answer 19

PFU: plaque-forming units (PFU/ml)

MOI: multiplicity of infection (PFU/cell)

Question 20

Diagnostics - options

Answer 20

Detection of viral material: PCR, ELISA, EM

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

Question 21

EM characteristics

Answer 21

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

Question 22

Neutralisation test

Answer 22

Neutralising ab bind GP > prevent entry.

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

Question 23

Entry of non-enveloped viruses

Answer 23

Pore formation:

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

(eg Polio)

Question 24

Entry of enveloped viruses

Answer 24

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

Porcesses: Priming, triggering

Question 25

Priming

Answer 25

Membrane fusion proteins (GPs) must be primed: sythesis as inactive precursors > cleavage by host cell protease eg Inluenza hemagglutinin prevents premature triggering

Question 26

Triggers of membrane fusion - ex

Answer 26

Receptor binding triggers membrane fusion (eg Avian retroviruses) Internalization into endosome > low pH triggers fusion (eg Influenza)

Question 27

Replication in DNA viruses

Answer 27

``` 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.

Question 28

Modes of DNA replication initiation

Answer 28

``` RNA primin (Polyomav.) Protein priming (Adenov.) Hairpin priming (Parvov.) ```

Question 29

RNA viruses - initiation of translation

Answer 29

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

Question 30

Picronavirus RNA

Answer 30

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

Question 31

Coding strategy of Picornaviridae

Answer 31

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

Question 32

Rhabdoviridae transcription

Answer 32

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

Question 33

Packaging of nucleic acids

Answer 33

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.

Question 34

Virus release strategies

Answer 34

1. Cell lysis (naked viruses) | 2. Budding (enveloped viruses

Question 35

Sites of budding

Answer 35

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

Question 36

ESCRT proteins

Answer 36

Facilitate membrane fission and particle release.

Question 37

Maturation

Answer 37

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