Viruses Intro Flashcards
Basic virus definition
Obligate intracellular parasite w/ genetic material (dna, rna, both) surrounded by protein coat/membrane
No metabolic activity of its own/not susceptible to antibiotics/
Most prevalent virus in human stool (also most prevalent other than bacteriophage)
Pepper Mild Mottle Virus
Describe a +ve sense vs -ve sense virus
Refers to direction of template strand
(+ve sense: 5’-3’; -ve sense: 3’-5’)
**can also be DS or SS, dna or rna)
What are the 3 types of viral genome structures?
Circular (e.g. HPV)
Linear (e.g. Adenovirus)
Segmented (e.g. Flu virus)
T/F: RNA viruses have polymerases just like DNA viruses
RNA viruses generally don’t have proofreading activity, unlike DNA viruses which do have proofreading activity, thus DNA virus mutation rate is generally lower
What enzyme is a key target for anti-viral therapy?
Viral Polymerases
Describe the basic structure of a virus
genetic material; surrounded by capsid +/- envelope +/- spike proteins
Which viral structure is used for binding and entry into host cells and is often the most antigenic region of the virus?
Spike proteins (only on enveloped viruses)
What is a nucleocapsid?
capsid bound to dna/rna
What are the 3 general types of viral classes?
Icosahedral (naked vs enveloped)
Helical
Complex
**note that this refers to how the virion forms/how the genetic material is arranged**
Describe the structure of a naked icosahedral virus
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
Describe the structure of an icosahedral enveloped virus
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
Describe the structure of an enveloped virus with a helical nucleocaspid
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
Describe the structure of a helical capsid virus
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
Describe the structure of a complex virus
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)
Name the replicative enzymes that viruses have (4)
DNA Polymerase
DNA-dependent RNA polymerase
RNA-dependent RNA polymerase
Reverse transcriptase
What is the “Baltimore Scheme” of classifying viruses?
Describe the classification of DNA viruses (hint: DNA viruses are hhappppy)
Herpesviridae, Hepadnaviridae, Adenovirus, Papilloma, Polyoma, Poxviridae, Parvovirus
**note that these all have icosahedral capsid except poxvirus**
Describe the classification of rna viruses
___ causes hand, foot and mouth disease
Coxsackie A virus
Which disease is this and which virus causes it?
Hand, foot and mouth disease
*Cocksackie A virus*
presents with vesicle on hands, feet and mouth; can be contagious
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)
Coxsackie viruses
Describe the pathogenesis of poliovirus
poliovirus infection >> (shed in feces) >> crossing GALT >> travel thru lymphatics >> travel thru blood >> viremia (onset of febrile illness) >> brain/cns >> meningitis/encephalitis/paralysis
While bacteria replicate via binary fission, viruses replicate by ___
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)
Describe the basic steps in the viral life cycle
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
How is a virus able to attach to and enter a host cell?
Virion attachment: viral surface protein recognizes receptor (can be protein or carbohydrates) on target cell
How are naked viruses released from the host cell after replicating?
Naked viruses rely on host cell lysis for release of new virions
How are enveloped viruses released from the host cell following replication?
Most enveloped viruses are released by budding at the plasma membrane
State 3 viral effects on host cells following infection
Acute cytopathic effect: host cells round up and die
Cell transformation - loss of normal growth control/oncogenic potential
No apparent effect
Describe the plaque assay for quantifying viruses
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)
What are 3 ways you could measure the amount of virus that’s causing infection?
Tissue culture assay
TCID50 (tissue culture infectious dose 50)
Focus forming assays
Describe how the TCID50 assay works
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
Describe how a focus assay works
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
