Virus classification, structure, and replication

Question 1

how was TMV discovered as a virus not bacteria?

Answer 1

it could pass thru a filter, and abcteria couldn;t bc size

Question 2

what is a bacteriophage

Answer 2

bacteria viruses with expanded virology and biology

Question 3

foot and mouth

Answer 3

1st animal virus

Question 4

yellow fever

Answer 4

first human virus

Question 5

are viruses smaller than bacteria, fungus, and other microbes?

Answer 5

yes

Question 6

biological classification of viruses

Answer 6

obligate intracellular parasites

Question 7

2 theories of virus origin

Answer 7

1. cellular: viruses were once cellular components but over time evolved separately
2. autopoietic: once autopoietic entities, became dependent on cells for replication

Question 8

what is virus classification based on

Answer 8

1. particle structure
2. genome
3. replication features
4. serology
5. stability

Question 9

what is particle structure

Answer 9

composition, shape, size

Question 10

nucleocapsid

Answer 10

• RNA/DNA in a core protected by a protein coat (capsid)
• structure that defines virus (helical, pleomorphic, icosahedral)
• composed on repeating protein units called capsomeres

Question 11

envelopes

Answer 11

virus modified cellular membranes acquired upon exit from host

*exposure to lipid solvents makes enveloped viruses non infectious

Question 12

smallest and largest virus

Answer 12

18 nm, 300 nm

Question 13

virus genome

Answer 13

composition can be single/double stranded DNA, single/double/ +ss, -ss RNA

Question 14

+ssRNA

Answer 14

may be directly translated

Question 15

-ssRNA

Answer 15

must be converted to + by RNA polymerase before translation

Question 16

steps of virus replication

Answer 16

1. attachment
2. entry
3. transcription
4. translation
5. genome replication
6. assembly
7. release

Question 17

attachment

Answer 17

• virus receptor -> cellular receptor
• viral receptors may require co receptors
• major determinant of host range (tropism)

Question 18

entry

Answer 18

• receptor mediated endocytosis OR direct penetration
• non enveloped viruses: thru pores (picornavirus), membrane disruption (adenovirus, reovirus)
• enveloped viruses: membrane fusion (influenza)

*many RNA viruses replicate in membrane complexes

Question 19

transcription

Answer 19

• production of mRNA for protein synthesis

- -ssRNA must bring own polymerase into cell

Question 20

translation

Answer 20

• protein production
• all viruses need cell’s ribosomes for this
• regulation of protein production can occur at transcript/translat level

Question 21

genome replication

Answer 21

• +ssRNA genome is template for translation, polymerase makes -ssRNA for new genomes
• -ssRNA: virus must include polymerase
• dsRNA: particle includes polymerase, innate immune response allows genome to stay in particle, mRNA synth in particle and released to cytoplasm, mRNA is + strand in genome
• ss/dsDNA: must gain access to nucleus, prepares cell for replication, genome is copied

Question 22

assembly

Answer 22

• packing new genomes into functional particles
• structural proteins help
• adenovirus: empty protein coat imports genome
• reovirus: RNA packed during capsid assembly
• retrovirus: preassembly on membrane

Question 23

release

Answer 23

• lysis: best known for bacteriophage
• weak lysis: dependent on membrane breakdown after cell death
• budding (enveloped only): cell membrane becomes outer coat of virus particle

Question 24

kinetics phases

Answer 24

eclipse: attachment and uptake
exponential growth: replication and assembly
plateau: cell death

Question 25

initial discovery of virus

Answer 25

1. disease in host

2. contamination in cell culture

Question 26

confirmation of virus

Answer 26

1. purification of virus
2. confirmation of disease
3. cell culture