Cytopathic Effects Of Viruses

Question 1

Cytopathic effects

Answer 1

Changes made to host cells infected by viruses by varied and complex mechanisms
Not all infections result in new virion production and significant changes could be induced without cell death resulting

Question 2

Categorisation

Answer 2

Cytocidal (lytic)

Non-cytocidal (non lytic)

Question 3

Cytocidal infection

Answer 3

Morphological cell changes
Inhib of pro, rna and dna synth
Cell death
Usually virions produced (CPE can occur in non productive infections)

Question 4

Persistent noncytocidal productive infection

Answer 4

No CPE
Little metabolic disturbance
Cells cont to grow and divide 
May cause loss of specialised fx
Always (often with red yield)

Question 5

Persistent noncytocidal nonproductive infection

Answer 5

Usually no effect on cell

No new virion production genome just persists as an episome or is integrated without expression

Question 6

Teansformational infection

Answer 6

Morphological alterations
Cells survive and become immortalised
Transformed cells may produce tumours
If oncogenic dna virus then they rarely produce new virions but oncogenic rna viruses sometimes do

Question 7

Shutdown of host macromolecular synth

Answer 7

Many cytocidal viruses cose for pros that shut down hist pro synth (cell rna and dna synth usually affected as a conseq) could be rapid or gradual shutdown
Noncytocidal viruses dont do generalised shutdown at all

Question 8

Flu macromol shutdown eg

Answer 8

Rna birus repl in nucleus
Needs capped rna as primers to initiate viral rna synth
Nuclear rna pol 2 transcripts are cleaved just before 5’ end by viral cap dep endonuclease (part of virus rna pol)
Aka cap stealing
Cap req for translation

Question 9

Herpes macro mol shutdown eg

Answer 9

Pro encoded by all herpes viruses redistrib spliceosomes and decr splicing as birus genes predominantly unspliced
HSV birion host shutoff pro is a struct pro carried in the virus that acts in the cytoplasm to resuce mRNa stability and cause an initial decr in amount of cellular mRNA

Question 10

Enterovirus macromol shutdown eg

Answer 10

Some encode a pro that alters ribosome sonit cant recog 5’ cap
Virus uses IRES for translation initiation so ribosomes preferentially act on viral mRNA

Question 11

Polio macromol shutdown eg

Answer 11

Encode proteases that cleave initiation factors and polyA binding pro si decr translation of cell mRNA and allows incr viral mRNA cont IRES

Question 12

Viral interference with apoptosis

Answer 12

Many encode antiapoptotic pros to prev cell death allowing virus to persist or complete replicative cycle
Others induce apoptosis in the infected cell, as a way to reduce inflam resp so red imm resp against virus

Question 13

Viral interference with cell cycle

Answer 13

Some induce cell to enter cell cycle to ensure replication machinery req by cirus is available
In lytic infections this isnt an issue but if infection is abortive this abnormal activation could lead to a tumour

Question 14

Viral interference with cell fusion

Answer 14

Glycoproteins that induce virus-cell fusion remain on CM of cell and can induce fusion with neighbouring cells in the same way by glycopro interact with rec on neighbouring cell
Can cause syncytia or polykaryocyte formation (a feature of cell monolayer infected with pox herpes corona or paramyxoviruses)

Question 15

Viral interference with permeability

Answer 15

Several cell fx triggered by depolarisation, so can be induced following virus infection
These changes may be swamped in lytic infections but can be key in nonlytic ones

Question 16

Cytoskel fx

Answer 16

Substrate for polyribosomes
Structural integrity
Struct framework for organelle movement
Part of system for cell movement

Question 17

Viral interaction with cytoskel

Answer 17

Many viral macromolec assoc with cytoskel and is likely that sub cellular compartmentalisation of viral processes relies on cellular organisation of host cell
Also cytoskel disrupt and so polyrib disrupt could partly explain inhib of host macromol synthesis

Question 18

miRNA fx

Answer 18

Act as key regulators of gene expression in mammals birds and other organisms

Question 19

miRNA production and process of action

Answer 19

Encoded by genome and expressed as longer RNAs processed by cellular enzymes to prod short hairpin RNAs
These dsRNA can recog a pro called Dicer and are incorporated into an RNA induced silencing complex that allows a strand of miRNA to bind a spec seq in target mRNA causing either degradation or inhib translation

Question 20

Viral interference with miRNAs

Answer 20

Most notably herpes viruses encode miRNAs that target cellular genes

Question 21

Mech of release of progeny virus dep on

Answer 21

Viral structure
Nucleocapsid bud through plasma mem prod EC virions or through internal mem (eg organelle mem or inner nuclear mem) and released via fusion of secretion vesicles cont virions

Question 22

Release from polarised (eg epi) cell

Answer 22

Can be directed to diff surf of cell eg basal or apical surf
Othro and paramyxo at apical surf
VSV and retro at basal surf
Glycopros of the viruses traffiked to the apprpriate surf (an innate property of glycopro struct and mimics cellular glycopro trafficking
Budding of many virions may disrupt the cell mem and cause CPE