intro to virology 6

Question 1

Match the virus with the virus family

Answer 1

ss DNA = Paroviridae
ds DNA = Papovaviridae, Adenoviridae, herpesviridae, poxviridae, hepadnaviridae

ds RNA = Reoviridae
- ssRNA = Orthomyxoviridae, paramyxoviridae, Rhabdoviridae, Bunyaviridae, arenaviridae, filoviridae
+ ss RNA = Togaviridae, flaviviridae, Coronaviridae, Retroviridae, Picornaviridae, Hepeviridae

Question 2

Describe properties of RNA viruses

Answer 2

• RNA is labile and transient
• Most RNA viruses replicate in cytoplasm
• CELLS CANNOT replicate RNA (RNA viruses must encode an RNA-dependent RNA polymerase)
• RNA viruses except (+) RNA genome, must carry polymerase
• RNA viruses are prone to mutation

Question 3

Describe the types of capsids

Answer 3

Helical
Icosahedral
complex

Question 4

Define Naked capsid

Answer 4

• Are environmentally stable to temp, acid, proteases, detergents, drying
• released from cell by lysis
• spread easily
• survive the adverse conditions of the gut
• resistant to detergents and poor sewage treatment

Question 5

Define Envelope viruses

Answer 5

• Environmentally labile, disrupted by acid, detergents, drying, heat
• Modifies cell membrane during replication
• are released by budding and cell lysis
• must stay wet
• CANNOT survive gastrointestinal tract
• spreads in large droplets, secretions, organ transplants, and blood transfusions
• DOES NOT NEED to kill the cell to spread

Question 6

Describe the virus life cycles

Answer 6

Attachement –> entry –> mRNA production –> protein and genome synthesis –> virion assembly –> egress

Question 7

Define plaque assay

Answer 7

DETECTS = Infectious virus
ADV = positivity shows active viral infection
LIMITS = restricted to viruses that replicate in tissue culture and produce cytopathic effect

Question 8

Election Microscopy

Answer 8

DETECTS = Virion Particles
ADV = Especially helpful in the identification of emerging viruses
LIMITS = Relatively expensive and technically challenging

Question 9

Antigen Detection = ELISHA

Answer 9

DETECTS = Viral proteins and glycoproteins
ADV = Sensitive and quick
LIMITS = requires specific antibodys

Question 10

PCR

Answer 10

DETECTS = DNA genomes
ADV = highly sensitive
LIMITS = DNA sequence information must  be available

Question 11

RT-PCR

Answer 11

DETECTS = RNA genomes
ADV = highly sensitive
LIMITS = RNA sequence must be available

Question 12

Western Blot

Answer 12

DETECTS = Anti-viral antibodies
ADV = sensitive and quick
LIMITS = time must be allowed for the initiation of the immune response.  Care must be taken to differentiate present from past infections

Question 13

How does ds DNA undergo Gene transcription

Answer 13

dsDNA uses cellular RNA pol to form mRNA

Question 14

How does ssDNA undergo gene transcription

Answer 14

ssDNA uses cellular DNA repair enzymes to form dsDNA and then utilizes cellular RNA pol to form mRNA

Question 15

How does retrovirus used +ssRNA to undergo gene transcription

Answer 15

+ssRNA (retrovirus) use viral reverse transcriptase to form dsDNA. Once dsDNA is formed then they use cellular RNA pol to form mRNA

Question 16

How does +ssRNA undergo gene transcription

Answer 16

+ssRNA do not need any enzymes to form mRNA. They are already in the correct configuration.

Question 17

How does -ssRNA undergo gene transcription

Answer 17

-ssRNA use viral RdRp (RNA-dependent-RNA polymerase) to form mRNA

Question 18

How does dsRNA undergo gene transcription

Answer 18

dsRNA utilize viral RdRp to form mRNA (similar to -ssRNA)

Question 19

Describe solutions to if cellular DNA replication machinery is not available at all time

Answer 19

• Make cellular DNA replication machinery available. (Papovaviruses stimualte cell growth and DNA synthesis)
• Encode viral proteins to synthesis genome (Poxviruses encode their own polymerase and enzymes to provide deoxyribonucleotides for DNA synthesis, replication machinery and transcption machinery in cytoplasm

Question 20

Describe solutions to if cellular RNA replication machinery is not available.

Answer 20

• Encode a RdRp in your genome (+ssRNA)
• Encode a RdRp in your genome and carry the enzyme in your virion (-ssRNA)

-ssRNA = Always Bring Polymerase Or Fail Replication = Arenaviridae, Bunyaviridae, Paramyxoviridae, Orthomyxoviridae, Filoviridae, Rhabdoviridae

Question 21

Describe general pathway to viral assembly and Egress

Answer 21

1) Individual viral proteins form into capsid subunits
2) subunits combine to form complete capsid
3) viral genome and other essential virion components are selectively packaged into capsids
4) Envelope is acquired (only for enveloped viruses)
5) virus exits cells
6) virions mature (only for certain viruses)

Question 22

Describe budding (only in envelope viruses)

Answer 22

similar to exocytosis:

1) RNA synthesized by virus accumulates and will form part of an envelope
2) modified region of host plasma membrane extends out from cell surface
3) modified region is pinched off from host cell, enclosing viral matrix protein and RNA within capsid; modified membrane and matrix form viral envelope

Question 23

describe Lysis

Answer 23

lysis of the cell is similar to poking holes in the cell. Kills the cell as virus leaves.