5: Multiplication

Question 1

Multiplication cycle of viruses?

short

Answer 1

• Adsorption
• Penetration
• Decapsidation
• Eclipse
• Maturation
• Release

Question 2

What happens during adsorption?

Answer 2

attachement to the host cell

Question 3

What happens during penetration?

Answer 3

entry into the host cell

Question 4

What happens during decapsidation?

Answer 4

nucleic acid release

Question 5

What happens during eclipse?

Answer 5

• expression and copy of the viral genetic information
• transcription, translation and NA replication
• different strategies according to the type of NA – > the Baltimore-system

Question 6

What happens during maturation?

Answer 6

• assembly of progeny virions
• Polipeptide –> protein
• Glycosylation, dimer formation, antigen development at the ER, Golgi

Question 7

What happens during release?

Answer 7

evacuation from the host cell

Question 8

What are the different types of receptors in Adsorption?

Answer 8

• cell surface receptor

- virus surface antireceptor

Question 9

What is characteristic for the Cell surface receptor of Adsorption?

Answer 9

• 10^4-5/cell (stable)
• usually already expressed in the embryo
• necessary for cellular functions
  (ie. CD4 - HIV, acetylcholine receptor - rabies virus)

Question 10

What is characteristic for the Virus surface antireceptor of Adsorption?

Answer 10

• more variable
• viruses adapt the cellular surface receptors dring their evolution
• related viruses usually target the same cell surface receptor
• sometimes non-related viruses have the same receptor
  (ie. CAR = Coxackie-adeno receptor)

Question 11

how is the stability of Virus surface antireceptor determined?

Answer 11

determined by the tissue or species receptor protein

Question 12

What happens if the Virus surface antireceptor is negatively charged?

Answer 12

• repulsion

- collision by chance

Question 13

What happens if the Virus surface antireceptor has reversible connection?

Answer 13

Cations neutralize the electrostatic power

Question 14

What happens if the Virus surface antireceptor has irreversible connection?

Answer 14

Chemical bonds between the proteins

Question 15

Penetration can be?

Answer 15

• energy dependent

- energy consuming

Question 16

What are the 2 forms of Penetration?

Answer 16

• General

- Alternative

Question 17

What are the General forms of penetration?

Answer 17

• Translocation
• endocytosis
• membrane fusion

Question 18

What are the Alternative forms of penetration?

Answer 18

• injection
• sexfimbria
• passive

Question 19

What is translocation?

penetration form

Answer 19

• ie picornavirus

- “trapdoor” mechanism, amorphous RNA-protein complex

Question 20

What is endocytosis?

penetration form

Answer 20

• mostly non-enveloped viruses + herpes, pox.

- cell nutrition endosome –> phagolysosome –> decapsidation

Question 21

What is membrane fusion?

penetration form

Answer 21

• only enveloped viruses
• viral fusion (F) protein induces
• the viral envelope merges into the cytoplasmic membrane of the host cell –> only the nucleocapsid gets into the cytosol

Question 22

What is injection?

penetration form

Answer 22

• tailed bacteriophage

- lysozyme enzyme + contractile proteins

Question 23

What is sexfimbria?

penetration form

Answer 23

• ribophages

- lack of cellular wall –> “bacterial sexual disease”

Question 24

What is passive?

penetration form

Answer 24

• plant viruses

- cellular wall injuries, arthropod bites

Question 25

Describe decapsidation

Answer 25

- uncoating - release of the NA from the capsid - dangerous for the virus, but necessary for the transcription

Question 26

What are the strategies of Decapsidation?

Answer 26

- use of cellular proteases (in lysosomes) - viral uncoating proteins (ie. poxviruses) - partial decapsidation - simulatneous penetration and decapsidation

Question 27

What is Partial decapsidation?

Answer 27

- hiding the NA until the early virus protein production | - ie. DNA viruses in the nucleus, Reo-, orthomyxo-, paramyxoviruses.

Question 28

How does simultaneous penetration and decapsidation happen?

Answer 28

by translocation and/or injection

Question 29

Where does Virus assembly occur?

Answer 29

Usually at the site of replication --> protection - RNA viruses + Pox, Asfarviridae --> cytoplasm - other DNA viruses --> nucleus

Question 30

Methods of virus assembly:

Answer 30

- the nucleic acid enters into the capsid --> Icosahedral | - The capsomers surround the nucleic acid --> helical

Question 31

What helps regulate the virus assembly?

Answer 31

Scaffolding proteins | - envelope and matrix proteins are acquired from cellular membranes.

Question 32

Types of Virus release

Answer 32

Passive/active way

Question 33

Virus release in Non-enveloped viruses:

Answer 33

- -> cytolysis - Rapid (picornav.) - Slow (Parvov.) - Apoptosis (adenoviridae)

Question 34

Virus release in Enveloped viruses:

Answer 34

Budding - Rapid (togav., paramyxov., rhabdov.) - Slow (arenav., retrov.)

Question 35

Budding sites of enveloped virus release:

Answer 35

Budding site is virus-specific. - Herpesv: nuclear membrane - Flaviv: ER - Coronav., Bunyav: Golgi - Asfarv., Togav., Orthomyxov., Paramyxov., Rhabdov: Cytoplasmic membrane

Question 36

Virus release in Cell-associated viruses (Gammaherpesvirinae):

Answer 36

release at cell death or injuries

Question 37

Virus release in Cell fusion (syncytium formation):

Answer 37

- -> membrane tunnels | - safe way of spreading (herpesv., paramyxov.)

Question 38

Alternative forms of virus release:

Answer 38

- lysosome disintegrations (herpesviridae) - T bacteriophages: lysyme enzyme digests the cellular wall - plant cells are firmly connected to each other: - -> virus spread from cell to cell - -> mosaic pattern