Viruses 1

Question 1

What is the one step viral growth cycle?

Answer 1

The time required for a single cycle of virus reproduction and yield of infectious virus per cell or burst size

Question 2

WHat is the eclipse phase?

Answer 2

intital infection is followed by disappearance of all viral particles

Question 3

What is the latent period?

Answer 3

viral genome takes over the control of the host cell protein making machinery and directs the production towards viral components

Question 4

Stages in viral replication

Answer 4

1. attachment to specific host cell receptors- determines what cell can be infected (tropism)
2. penetration
3. uncoating- release of nucleic acid
4. macromolecular synthesis
5. postranslational modification of proteins
6. assembly of new virus particles
7. release- lysis of the cell or budding out

Question 5

What is the macromolecular synthesis

Answer 5

early mRNA and protein synthesis- proteins to shut off host cell; proteins to replicate viral genome

replication of the genome

late mRNA and protein synthesis: structural proteins

Question 6

What are the 2 different bacteriophages?

Answer 6

1. lytic/virulent phase- kills the host immediately
2. lysogenic phase (lysogeny)- occurs when the host is not immediately killed and the phage genome becomes a prophage via integration into the host chromosome or exist as an independent entity but replicating with the rate equal to the host genome multiplication

Question 7

Tropism

Answer 7

limited to a single organ, tissue, specialized cell type or range of different organs and tissues

Question 8

What factors define a tropism?

Answer 8

susceptibility- Viral glycoproteins integrated in the outer coat- either the capsid or the envelope that target receptors are acting as doors on the surface of the host cells

presence of transcription factors allowing expression of viral genes

permissivity- presence of cell enzyme pathways to produce viral proteins

Question 9

Attachment

Answer 9

interaction between a virus and its target cell

critical step as a determinant of target selection by many viruses

requires viral attachment protein and cellular receptors

Question 10

penetration and uncoating enveloped viruses

Answer 10

1. fusion- virus glycoproteins attach to host cell receptors, envelope membrane fusion occurs, capsid enters, is uncoated and virus is released ex: paramyxovirus, HIV
2. endocytosis and acidification- host cell cytoplasmic membrane wraps around virus and brings it inside, the capsid is uncoated and the viral genome is released into the host cell ex: influenza

Question 11

penetration and uncoating non-enveloped viruses

Answer 11

1. direct entry across plasma membrane- virus attaches to host cell receptors, sinks into cell membrane, and injects its genome through a pore into the cell; ex- poliovirus
2. endocytosis- host cell cytoplasmic membrane wraps around virus and brings it inside, the capsid is uncoated and the viral genome is released into the host cell; ex- parvovirus

Question 12

viral replication

Answer 12

uncoating of viral genome-> transcription or expression of mRNA-> translation of mRNA generates the early proteins- synthesis of viral DNA or RNA polymerase and other proteins which play an important role in viral replication-> viral genome replication leads to complementary strand synthesis and additional templates using nucleic acids-> late mRNA synthesis generates late proteins which participate in the formation of the viral capsomeres-> capsid formation follows a self-assembly mechanism in most of the cases

Question 13

viral release

Answer 13

2 means of release

1. exocytosis causes the viral capsid to grab cellular membrane in a form of an envelope which is laced with viral proteins- mostly in enveloped viruses
2. cell lyses- non enveloped viruses

Question 14

understanding viral genomes

Answer 14

understand baltimore classification and the phylogenetic relationship between viruses

modes of genome replication and viral propagations

opportunities for anti-viral treatment and host immunity

Question 15

All viruses..

Answer 15

go through mRNA positive strand synthesis to produce proteins

are haploid (except retroviruses)

DNA based presented by single molecule, either dsDNA or ssDNA

RNA based presented bu either single molecule or several molecules

Question 16

Gene coding strand?

Answer 16

positive nucleic acid or the actual gene sequence

Question 17

complementary strand to the gene coding mRNA

Answer 17

negative nucleic acid or the template strand

Question 18

viral genome of Reovirus

Answer 18

dsRNA, segmented genome

Question 19

viral genome or Retroviruses

Answer 19

postitive ssRNA

HIV- diploid genome

Question 20

viral genome of Orthomyxovirus

Answer 20

negative ssRNA

segmented genome

Question 21

arenavirus and bunyavirus genome

Answer 21

negtive ssRNA

have ambisense genome where part of the ssRNA is negative

Question 22

viral replication

Answer 22

process of generating new genomes
special cases require specific viral enzymes: RNA dependent DNA polymerase (reverse transcriptase) and RNA dependent RNA polymerase (RNA replicase)

Question 23

3 ways of producing viral proteins with single function

Answer 23

transcription of individual monocistronis mRNA molecules from the genome

segmented genome where each molecules gives single monocistronic mRNA

production of a single long polyprotein that is later cleaved into individual functional peptides

Question 24

examples of viral proteases as essential targets in antiviral atrategies

Answer 24

1. Boceprevir-mediated inhibition of Hep C virus polyprotein processing
2. Saquinavir-mediated inhibition of HIV gag and gag-pol polyprotein processing

Question 25

defective satellite viruses

Answer 25

atypical virus, cant replicate without a helper virus- up to 100x more defective viruses are produced than normal viruses due to genome mutations

Question 26

example of defective virus

Answer 26

Hep D

small ssRNA virus that can only infect in the presence of hep B

shows replication similarities with viroids in plants

produces an antigen termed delta antigen

utilizes HBV surface antigen for entry into host

Question 27

Prion characteristics

Answer 27

no genome

adopt a modified structure/folding compare to the noninfectious folding of the same protein

Question 28

What do prions cause?

Answer 28

loss of motor control, dementia, paralysis, encephalitis, widespread neuronal loss

Question 29

Prion mode of transmission and function

Answer 29

can be acquired through diet, transfusion, surgical procedures, corneal transplants

hereditary- AD mutation of PrP on ch 20- 10-15% of cases

spontaneous- rate of 1/ mill people usually late in life

normal PRPc can change to harmful PrPsc via a chain reaction- forming long filamentous aggregates that gradually damage neuronal tissue

Question 30

viroids

Answer 30

plant pathogen

smallest infectious pathogen composed of a short strand of circular, ssRNA molecule that do not encode any protein

distributed via plasmodesmata

likely to interfere with RNA regulation such as siRNA causing

responsible for causing disease in a number of plants, potatoes, tomatoes, cucumbers