Virology1

Question 1

briefly explain the history of virology

Answer 1

• filterable agent infectivity for TMV & foot and mouth disease virus
• first human virus described causes yellow fever
• filterable viruses = Rinderpest, Vaccinia, Rabies, Cassava mosaic
• Avian leukosis & poliomyelitis & chicken sarcomas shown to be caused by viruses
• bacterial viruses discovered
• spanish flu pandemic

Question 2

what are 6 characteristics of viruses?

Answer 2

• small & infectious (20nm - 300nm)
• acellular pathogens
• obligate intracellular parasites (host & cell-type specificity)
• DNA/RNA genome (never both)
• lack genes for products needed for reproduction
• infect all types of cells

Question 3

what is a virus’ genome surrounded by?

Answer 3

protein capsid (sometimes a phospholipid membrane w viral glycoproteins)

Question 4

what are virions?

Answer 4

virus particles viruses reproduce through the exploitation of host-cell genomes

Question 5

what are capsomers?

Answer 5

• small structural unit that makes up a capsid
• are an outer covering for the protection of the genetic material of a virus

Question 6

what is a nucleocapsid?

Answer 6

capsid + genome

Question 7

what are peplomers?

Answer 7

viral proteins that modify a virus envelope that was acquired from nuclear or plasma membrane of the infected host cell

Question 8

what are the arguments for viruses being non-living? (4)

Answer 8

• acellular
• no cell nucleus, organelles or cytoplasm
• can’t move
• can’t reproduce

Question 9

what are the arguments for classifying viruses as living? (4)

Answer 9

• can only reproduce in living cells
• obligate intracellular parasite
• can evolve
• genetic material

Question 10

what type of microscope do you need to see viruses?

Answer 10

electron microscope

Question 11

what’s the difference between the phylogeny of viruses and bacteria?

Answer 11

viruses → tangled
bacteria → natural

Question 12

do viruses have ribosomes?

Answer 12

no

Question 13

what are naked (nonenveloped) viruses ?

Answer 13

viruses that don’t have an envelope

Question 14

what type of capsid structure is found in enveloped and nonenveloped viruses?

Answer 14

enveloped = helical
non enveloped & enveloped = icosahedral

Question 15

which type of DNA virus isn’t icosahedral?

Answer 15

poxvirus

Question 16

what are 3 characteristics of RNA viruses?

Answer 16

• ss/self-duplicating RNA
• high mutation rate
• all plant viruses

Question 17

explain positive/negative sense of RNA

Answer 17

Positive sense (+sense) RNA = mRNA
Negative sense (-sense) RNA = Requires RNA polymerase to be converted to +sense RNA

Question 18

what are 3 characteristics of DNA viruses?

Answer 18

• DNA dependent and replicate using DNA pol
• dsDNA but sometimes can be ssDNA
• most animal viruses are DNA viruses

Question 19

what are 3 types of viruses (ito what they infect)?

what type of genetic material does each type have

Answer 19

• animal viruses → DNA or RNA
• plant viruses → RNA
• bacteriophage → DNA

Question 20

what are the different ways in which viruses can be transmitted?

Answer 20

direct contact, indirect contact with fomites or through a vector (mechanical or biological)

Question 21

what are zoonoses and reverse zoonoses?

Answer 21

zoonoses → transfer from animal to human
reverse zoonoses → transfer from human to animal

Question 22

what are the four viral structures?

+ describe them

Answer 22

• helical (nucleic acid is spiral w capsomers helically around coil)
• icosahedral (spherical shape w nucleic acid inside capsid, composed of 20 triangular faces)
• spherical (round & some have spikes)
• complex (don’t confirm into any category i.e. bacteriophages, poxvirus)

Question 23

what does a species, genus, subfamily, family and order refer to?

Answer 23

• species → pop of viruses that share distinct pool of genes
• genus → group of related viral species
• subfamily → group of related viral genera
• family → group of a related subfamily
• order → group of family

Question 24

what are the 3 criteria for clasification of viruses?

+ brief explanation

Answer 24

• morphology (size & shape, presence of envelope)
• structural protein (contributes to molecular weight of virion)
• nucleic acid properties (ds/ss, positive/negative sense sequence)

Question 25

what do segmented genomes do?

Answer 25

facilitate exchange of genome segments between different virus strains during coinfection of a single host cell (viral reassortment)

Question 26

what are the 2 major priorities of the virus life cycle?

Answer 26

* make viral proteins * make copies of the viral genome

Question 27

what are the different polymerases and what do they do?

Answer 27

* **DdDp** DNA dependent DNA pol = synthesises DNA from DNA (**DNA → DNA**) * **DdRp** DNA dependent RNA pol = synthesises RNA from DNA (**DNA → RNA**) * **RdRp** RNA dependent RNA pol = synthesises RNA from RNA (**RNA → RNA**) * **RdDp** RNA dependent DNA pol = synthesises DNA from DNA (**RNA → DNA**) (**REVERSE TRANSCRIPTASE**)

Question 28

what is the baltimore scheme?

Answer 28

a system that divides viruses into g**enome type** and the **mechanism of mRNA production**

Question 29

what are class i viruses? | + examples + type of enzyme (pol)

Answer 29

ds DNA mRNA transcribed directly from DNA template | e.g. herpesvirus, adenovirus, most bacteriophages ## Footnote dddp → copy + & - to produce dsDNA ddrp → copy - into mrna → into proteins using host's ribosomes

Question 30

what are class ii viruses? | + examples

Answer 30

ssDNA DNA coverted to double stranded before RNA is transcribed | e.g. canine parvovirus ## Footnote dddp → copy + to produce dsDNA intermediate ddrp → copy - strand of dsdna intermediate to produce + viral mRNA → translated into viral protein dddp → copy - dsdna intermediate strand to produce ss(+) DNA viral genome

Question 31

what are class iii viruses?

Answer 31

dsRNA mRNA transcribed from RNA genome | e.g. rotavirus (childhood gastroenteritis) ## Footnote rdrp → copy both + & - to produce dsRNA genome rdrp → copy - into + viral mRNA → translated into viral proteins

Question 32

what are class iv viruses? | + examples

Answer 32

ssRNA (+) genome functions as mRNA | e.g. coronavirus, pircornavirus (common cold), polio ## Footnote rdrp → copies + to produce -ssRNA → rdrp copies - to produce +ssRNA viral genome translated into viral protein

Question 33

class v viruses | + examples

Answer 33

ssRNA (-) mRNA transcribed from RNA genome | e.g. rabies or influenza ## Footnote rdrp → copies - RNA to produce +ssRNA → rdrp copies +ssRNA to produce -ssRNA viral genome rdrp → copies -RNA to form + viral mRNA → translated into viral proteins

Question 34

class vi viruses | + examples

Answer 34

ssRNA viruses w reverse transcriptase reverse trans → makes ssDNA from RNA genome → DNA incorporated into host genome → mRNA transcribed from incorporated DNA | e.g. HIV ## Footnote reverse transcriptase possesses ribonuclease activity → degrade RNA strand of RNA-DNA hybride reverse transcriptase → used as DNA pol to yield dsDNA → insert into host = provirus

Question 35

class vii viruses | + examples

Answer 35

dsDNA w reverse transcriptase DNA is replicated thru RNA intermediate (may serve directly as mRNA or template to make mRNA) | e.g. hepatitis B virus

Question 36

what is a provirus?

Answer 36

can remain latent indefinitely or cause expression of viral genes, leading to production of new viruses