Exam 3 - Viruses

Question 1

Classical System of Virus classification

Answer 1

Nature of genetic material (DNA vs. RNA)
Symmetry of capsid (helical/icosahedral)
Naked or enveloped
Dimensions of virion and capsid

Question 2

Baltimore System

Answer 2

Based on central dogma

Categorized on how virus produces mRNA

Question 3

Two principles of virus genomes

Answer 3

1. Serve as template for progeny (small, finite number of NA copying stratigies)
2. Function is to make mRNA (parasite of host cell translation system)

Question 4

7 Classes of viral genome configuration

Answer 4

dsDNA
gapped circular dsDNA (can be combined with dsDNA)
ssDNA
dsRNA
ss(+)RNA
ss(-)RNA
ss(+)RNA with DNA intermediate

Question 5

Function of virion proteins

Answer 5

Protection of genome
Delivery of genome
Mediate interactions with host

Question 6

Capsids

Answer 6

Identical subunits to protect genome non-covalently bound
Helical
Icosahedral

Question 7

Envelope Functions

Answer 7

Not all viruses have (lipid bilayer with glycoprotein spikes)
Entry and host range determination
Assembly and egress
Evasions for the vertebrate immune system

Question 8

Replication - Eclipse period

Answer 8

No detectable virus in/outside of cell

Virus disassembled and released genome

Question 9

Replication - Latent period

Answer 9

Time from initation to release of new, infectious virus

Beginning of extracellular detection

Question 10

Viral steps during latent period

Answer 10

Attachment
Entry/uncoating
Viral gene expression (need switch to occur)
Viral genome replication
Assembly of new viruses and egress

Question 11

Viral attachment receptors

Answer 11

proteins (usually glycoproteins)
carbohydrates (less specific)
Need proximity (electrostatic) and interaction (binding)
Often more than one receptor and combo

Question 12

Viral entry

Answer 12

Endocytosis
Fusion and entry (enveloped viruses)
Energy dependent, cell must be metabolically active

Question 13

Susceptible cell
Resistant cell
Permissive cell

Answer 13

Susceptible: has functional receptor
Resistant: does not have functional receptor
Permissive: capacity to replicate virus
Need both susceptible and permissive

Question 14

Gene expression in RNA viruses

Answer 14

All encode for RNA-dependent RNA polymerase RdRp

Can initiate or extend primer

Question 15

Viral assembly

Answer 15

Helical: RNA is coated as it is synthisized
Icosahedral: capsid assembled around or genome fed into premade capsid

Question 16

Viral egress

Answer 16

Naked: cell lysis
Enveloped: membrane budding and exocytosis

Question 17

Innate Defense against viruses

Answer 17

1. Barrier/cells
2. Intracellular restriction factors
3. TLR’s and Helicases

Question 18

Intracellular (host) restriction factors

Answer 18

APOBEC (incorporated into and damages genetic material)

TRIM5

Question 19

HIV resistance to APOBEC

Answer 19

Via Vif protein

1.