Virus structure and function

Question 1

Property of virus

Answer 1

submicroscopic, obligated intracellular parasite, uses host to replicate ans assemble progeny

Question 2

Viral Classical system:

Answer 2

Nature of genetic material (DNA/RNA)
Symmetry of capsid
Naked/enveloped
Dimensions of virion/capsid

Question 3

Baltimore system viral calssificaiton based on:

Answer 3

Central dogma (DNA, RNA, Proteins)

Question 4

Baltimore first principle

Answer 4

Small finite number of nucleic acid copying strategies

Question 5

Baltimore second principle

Answer 5

Viral genome in cell makes mRNA (viral genome must provide mechanisms for syn of mRNA)

Question 6

7 classes of viral genome configuration

Answer 6

dsDNA
gapped circular dsDNA
ssDNA
dsRNA
ss+ RNA
ss- RNA
ss+ RNA with DNA intermediate

Question 7

3 main function of virion proteins

Answer 7

protection of genome
Delivery of genome
Mediate interaction with host

Question 8

Two hypes of capsids

Answer 8

helical and icosahdral

Question 9

Helical capsids arranged by:

Answer 9

identical subunits - rotational symmetry/irregularly shaped protein –> disk

Question 10

Icosahedral capsids are:

Answer 10

form hollow quasi-spherical structure with genome inside.

Question 11

Envelopes - define and source

Answer 11

lipid bilayers during assembly/budding - with viral glycoproteins embedded

plasma membrane, ER, golgi

Question 12

Envelope functions

Answer 12

entry and host range determination
Assembly/egress
Evasion from immune sys

Question 13

Describe growth curve of virus life cycle

Answer 13

One step
Eclipse phase
Latent period
plaque forming units shoots up after latent period

Question 14

Eclipse period:

Answer 14

particles broken down, release genome

No PFU - Not infectious

Question 15

Latent period

Answer 15

Time from initiation of infection to release infectious virus particle from cell

Question 16

5 main things happen during latent period:

Answer 16

attachment of virus to cell
Entry of virus into cell/uncoating of viral genome
Viral gene expression
viral genome replication
assembly of new virus/egress to new particles

Question 17

Carbohydrate receptor tend to be _____ ______ than protein receptor (and why)

Answer 17

less specific

Same config of carb side chain on many diff glycosylated membrane bound molecules

Question 18

Entry is an energy ______ process

Answer 18

dependent (cell must be metabolically active)

Question 19

2 ways for virus to enter cell

Answer 19

endocytosis -> nedosomes -> escape

Enveloped -> fusion with cell membrane

Question 20

Uncoating (define)

Answer 20

viral particle enter cell, capsid removed, genome exposed

Question 21

Gene expression for DNA virus

Answer 21

ds, gapped, ss = transcribe mRNA using (-) strand as template
Uses: Host RNA pol II (nucleus)
mRNA capped/poly adenylated

Question 22

Poxviruses are unqiue in their gene expression - why?

Answer 22

replicate in cytoplasm - encodes own RNA polymerase

Question 23

All RNA viruses make an viral enzyme called ____________?

Answer 23

RNA-dependent RNA polymerase (RdRp)

Question 24

RdRp function

Answer 24

production of mRNA and replication of RNA genomes

Question 25

+ vs - strand RNA virus gene expression

Answer 25

+ = translated directly by cellular ribosomes. Amp of mRNA copy number/subgenomic mRNA by RdRp - = transcribe + mRNA package RdRp in virus particle

Question 26

Retroviruses uses what enzyme?

Answer 26

reverse transcriptase - RNA to DNA - integrate into host - transcribed with host cell encoded RNA pol II

Question 27

dsDNA viral replicate (location and methods)

Answer 27

1. nuclear - cellular factor, viral pol, accessory factors | Cytoplasm - largely independent of cell machinery

Question 28

ssDNA virus replicate (location)

Answer 28

nucleus | forms ds intermedate - template for syn ssDNA

Question 29

Gapped circular ds DNA replicate

Answer 29

Virally encoded reverse trasncriptase - mRNA to DNA viral genome Gaps must be filled in before transcribed

Question 30

Icosahedral capsids packaging of genome by (1) or (2)

Answer 30

(1) capside assembles around genome | (2) genome fed into preformed capsids

Question 31

Egress by naked capsids viruses typically ______

Answer 31

cell lysis

Question 32

Egress by enveloped typically

Answer 32

budding From plasma membrane - extracellular environment directly From ER/Golgi - secreted from infected cell

Question 33

Primary initial routes of virus infection:

Answer 33

respiratory, alimentary, genitourinary | Also: mucous membrane, skin abrasion, parentally

Question 34

Successful initial infection requires?

Answer 34

Sufficient virus, host susceptible, host permissive, low host defense

Question 35

Sufficient virus

Answer 35

free virus particle must sruvive environmental exposure/abundant enough in concentration

Question 36

Tropism defined as:

Answer 36

infect certain tissues and not other - tissue specificity

Question 37

site of initial replication (local/systemic)

Answer 37

Epithelium both

Question 38

Secondary replication sites (local/system)

Answer 38

none | lymphoid organs, lungs, skin

Question 39

Incubation and immunity (local vs systemic)

Answer 39

1-3 days vs 10-21 days | Short vs lifelong

Question 40

Antibody to resist acute local/systemic?

Answer 40

Local: IgA Systemic: IgG and IgA

Question 41

Chronic viral infection described as

Answer 41

ongoing infection/replication with mild/inapparent disease

Question 42

Persistent vs latent

Answer 42

continue to produce new virus vs No infection detected but can reactivate/recrudescence

Question 43

Slow chronic infection

Answer 43

no symptoms initially, long incubation, may induce immune response. Eventually deterioration/death

Question 44

Example of acute local, systemic, chronic, latent, slow

Answer 44

``` cold/diarrhea Smallpox/measles Rubella VZV AIds, cancer ```

Question 45

Transforming viral infection: define

Answer 45

integrate to host -> activate/supress oncogene/TSG Tumorigenesis