Viruses Intro

Question 1

Basic virus definition

Answer 1

Obligate intracellular parasite w/ genetic material (dna, rna, both) surrounded by protein coat/membrane

No metabolic activity of its own/not susceptible to antibiotics/

Question 2

Most prevalent virus in human stool (also most prevalent other than bacteriophage)

Answer 2

Pepper Mild Mottle Virus

Question 3

Describe a +ve sense vs -ve sense virus

Answer 3

Refers to direction of template strand

(+ve sense: 5’-3’; -ve sense: 3’-5’)

**can also be DS or SS, dna or rna)

Question 4

What are the 3 types of viral genome structures?

Answer 4

Circular (e.g. HPV)

Linear (e.g. Adenovirus)

Segmented (e.g. Flu virus)

Question 5

T/F: RNA viruses have polymerases just like DNA viruses

Answer 5

RNA viruses generally don’t have proofreading activity, unlike DNA viruses which do have proofreading activity, thus DNA virus mutation rate is generally lower

Question 6

What enzyme is a key target for anti-viral therapy?

Answer 6

Viral Polymerases

Question 7

Describe the basic structure of a virus

Answer 7

genetic material; surrounded by capsid +/- envelope +/- spike proteins

Question 8

Which viral structure is used for binding and entry into host cells and is often the most antigenic region of the virus?

Answer 8

Spike proteins (only on enveloped viruses)

Question 9

What is a nucleocapsid?

Answer 9

capsid bound to dna/rna

Question 10

What are the 3 general types of viral classes?

Answer 10

Icosahedral (naked vs enveloped)

Helical

Complex

**note that this refers to how the virion forms/how the genetic material is arranged**

Question 11

Describe the structure of a naked icosahedral virus

Answer 11

Has protein shell on outside + genome on the inside (no envelope)

**Icosahedral naked viruses are very stable because of the protein shell. Since they resistant most other methods of killing, the only thing that kills them is above 4% bleach**

**

examples of naked icosahedral viruses:

norovirus, rhinovirus

Question 12

Describe the structure of an icosahedral enveloped virus

Answer 12

Pretty much the same as a naked icosahedral virus except it has an envelope composed of lipids and proteins

**not as stable as non-enveloped viruses**

examples of enveloped viruses:

Varicella Zoster, EBV, Cytomegalovirus

Question 13

Describe the structure of an enveloped virus with a helical nucleocaspid

Answer 13

Basically similar to enveloped icosahedral except:

a. has a nucleocaspid that wraps around genome instead of an actual capsid
b. has envelope made of glycoproteins and lipids

**less stable than non-enveloped icosahedral virus**

example: Influenza virus

Question 14

Describe the structure of a helical capsid virus

Answer 14

Bullet that covers viral genome: repeating viral proteins wrapped around genetic material and shape into this bullet structure. Over top of it are capsid proteins (glycoproteins)

**Note that the capsid proteins self assemble**

(basically the genetic material is just wrapped up into a helical structure, that is the capsid)

**

example: Rabies virus

Question 15

Describe the structure of a complex virus

Answer 15

combination of icosahedral and helical shape with a complex outer wall or head to tail morphology (like bacteriophage)

double lipid membrane w/ viral proteins, core w/ proteins for uncoating + replication (e.g poxvirus)

Question 16

Name the replicative enzymes that viruses have (4)

Answer 16

DNA Polymerase

DNA-dependent RNA polymerase

RNA-dependent RNA polymerase

Reverse transcriptase

Question 17

What is the “Baltimore Scheme” of classifying viruses?

Answer 17

Question 18

Describe the classification of DNA viruses (hint: DNA viruses are hhappppy)

Answer 18

Herpesviridae, Hepadnaviridae, Adenovirus, Papilloma, Polyoma, Poxviridae, Parvovirus

**note that these all have icosahedral capsid except poxvirus**

Question 19

Describe the classification of rna viruses

Answer 19

Question 20

What are 3 mechanisms of viral pathogenesis?

Answer 20

infected host cell destruction

modification of host cell function

immune and inflammatory response to viral infection (immune response actually causes damage, not so much infection itself)

Question 21

Which viruses make up the Picorna viruses?

Answer 21

Picorna viruses (P_K_HR_E_na viruses)

Parechovirus

Kobuvirus

Enteroviruses

Hepatoviruses

Rhinoviruses

**Small rna viruses (very tiny genome) (made up of capsid and rna); fast replication (8-12hrs)**

Question 22

___ causes hand, foot and mouth disease

Answer 22

Coxsackie A virus

Question 23

Which disease is this and which virus causes it?

Answer 23

Hand, foot and mouth disease

*Cocksackie A virus*

presents with vesicle on hands, feet and mouth; can be contagious

Question 24

The most common (virus) cause of the common cold is __

Answer 24

Rhinovirus

*other viruses to consider:

Coronavirus (related to SARS/MERS)

Respiratory Syncytial Virus (RSV)

Parainfluenza

Adenovirus*

Question 25

What are 2 diseases caused by Parechovirus and Kobuvirus?

Answer 25

Parechovirus: mycocarditis, encephalitis Kobuvirus: gastroenteritis (think eating bad Kobbage you get bad diarrhea)

Question 26

Which virus causes a disease (name the disease - affects the eyes) characterized by a “sensation of something in the eye”?

Answer 26

Cocksackie A virus

Question 27

Cocksackie __ viruses can cause \_\_\_, which is characterized by "Devil's grip" aka pleurodynia

Answer 27

**Cocksackie B** viruses can cause **severe thoracic pain**, which is characterized by "Devil's grip" aka **pleurodynia**

Question 28

Herpangina, a disease characterized by ulcerated, painful lesions in the palate and tonsils, is caused by ___ (group of viruses, hint: same ones that cause hand, foot and mouth disease)

Answer 28

Coxsackie viruses

Question 29

Describe the pathogenesis of poliovirus

Answer 29

poliovirus infection \>\> (shed in feces) \>\> crossing GALT \>\> travel thru lymphatics \>\> travel thru blood \>\> viremia (onset of febrile illness) \>\> brain/cns \>\> meningitis/encephalitis/paralysis

Question 30

What is the emerging, biennial, polio-like disease characterized by symmetric flaccid paralysis?

Answer 30

Acute Flaccid Myelitis \*\*potentially caused by enterovirus 71\*\*

Question 31

While bacteria replicate via binary fission, viruses replicate by \_\_\_

Answer 31

Viruses replicate by xeroxing: one virus replicates inside a cell and then has a burst size (how many virions are popped out of the cell)

Question 32

Describe the basic steps in the viral life cycle

Answer 32

**Attachment** to host cell via receptors \>\> **penetration** thru an entry vesicle \>\> **uncoating** (depending on enveloping) \>\> genome needs to get to appropriate location to start replication (nucleus, cytosol or padox) \>\> **synthesize** viral mrna, translation of viral proteins using host machinery, genome replication \>\> **assembly** of viral components (capsid proteins are self-assembling) \>\> **exit and maturation**

Question 33

How is a virus able to attach to and enter a host cell?

Answer 33

Virion attachment: viral surface protein recognizes receptor (can be protein or carbohydrates) on target cell

Question 34

What are the host cell receptors for the following viruses: HIV Epstein Barr Rhinovirus Influenza

Answer 34

HIV - CD4 Epstein Barr - CD21 Rhinovirus - ICAM1 Flu - Sialic acid

Question 35

How are naked viruses released from the host cell after replicating?

Answer 35

Naked viruses rely on host cell lysis for release of new virions

Question 36

How are enveloped viruses released from the host cell following replication?

Answer 36

Most enveloped viruses are released by budding at the plasma membrane

Question 37

What are the outcomes (**cellular level**) of viral infection?

Answer 37

Productive infection - generally leads to cytopathic effect with a burst of virus production (infection might be limitedin host, e.g. 72 hour course fo rhinovirus) Latent infection - no production of infectious virus particles, but genetic information of the virus remains Persistent infection - chronic virus production Abortive infection - virus life cycle incomplete and virus lost

Question 38

What the outcomes of viral infection at the organism level?

Answer 38

Inapparent infection (pt is asymptomatic) \>\> acute infection \>\> latent (recurrent) infection \>\> persistent infection

Question 39

State 3 viral effects on host cells following infection

Answer 39

Acute cytopathic effect: host cells round up and die Cell transformation - loss of normal growth control/oncogenic potential No apparent effect

Question 40

Describe the plaque assay for quantifying viruses

Answer 40

Limiting dilutions of virus then you plate \*\*plaque – visible loss of cells following viral infection\*\* Bigger plaque – more spread of virus/faster growth of virus/greater death of human cells (or whatever cells are being used)

Question 41

What are 3 ways you could measure the amount of virus that's causing infection?

Answer 41

Tissue culture assay TCID50 (tissue culture infectious dose 50) Focus forming assays

Question 42

Describe how the TCID50 assay works

Answer 42

TCID50 - tissue culture infectious dose 50 – the number of wells whereby 50% of the wells contain a virion, vs 50% of the wells that don’t have a virion

Question 43

Describe how a focus assay works

Answer 43

Focus assay: instead of counting death (like plaques), you count rapid growth of cells in small area \*\*note that this and TCID 50 are used for viruses that induce cell proliferation