LG6.8 virology

Question 1

describe the capsid structure:

Answer 1

If virus only has capsid, it’s called naked. these viruses are hardy 1. viral genomes inside this structure 2. capsid made of many viral proteins 3. protects the genome and gives shape 4. may interact with cells and immune system

Question 2

describe the capsid surface structure

Answer 2

Used for attachment & penetration; may also be involved in release, maturation or immunity - include glycoproteins

Question 3

give a few characteristics of an enveloped virus:

Answer 3

1. more sensitive to alcohol, heat, detergents, etc. than naked virus. “They don’t like to be out the environment for too long”
2. enveloped virus budding: virus usually gets its envelope from the host cell membrane

Question 4

describe RNA genomes:

Answer 4

RNA genomes may be positive-sense, negative-sense, or ambisense; may also be segmented; usually linear

Question 5

what’s ambisense?

Answer 5

has + and - sense RNA in genome

Question 6

what is it mean when a RNA genome is segmented?

Answer 6

kind of like having its own set of ‘chromosomes’

Question 7

describe viral DNA genomes.

Answer 7

may be linear or circular; usually single copy (except HIV is diploid)

Question 8

list the steps in viral pathogenesis

Answer 8

1Viral encounter with and entry into the host
2Viral growth after entry
3Avoidance of innate (& adaptive) host defenses
4Tissue invasion and tropism
5Tissue damage and disease
6Transmission to new hosts

Question 9

describe viral attachment: (aka adsorption):

Answer 9

random collision of virus with target, interaction with host cell receptor(s), fluid nature of membrane allows entry

Question 10

list the 3 ways viri gain entry into host cells.

Answer 10

1. Direct fusion 2. endocytosis (aka viropexis) 3. barteriophages

Question 11

once in the host cell, where do DNA viruses spend most of their time? RNA viruses?

Answer 11

nucleus. cytoplasm

Question 12

what’s the central dogma of biology?

Answer 12

DNA gets transcribed to mRNA which gets translated into protein. And DNA is replicated

Question 13

How does double stranded DNA virus make protein?

Answer 13

just like eukaryotic host cell. May even use host polymerase 2 to help make mRNA from DS DNA. this happens in the nucleus. Then translation happens in cytoplasm (locations identical to eukaryotic versions)

Question 14

How do + strand viruses make protein?

Answer 14

these single strands of RNA are translated (in cytoplasm) to protein in target cell directly upon infection

Question 15

How do - strand viruses make protein?

Answer 15

these viruses pack their own RNA transcriptase to replicate strand of RNA into + sense RNA. Then + sense strand is translated into protein

Question 16

How do retroviruses make protein?

Answer 16

1. These bring reverse transcriptase and change their single strand RNA strand to DNA then 2. DNA is replicated to double strand DNA. then 3. DNA is transcribed to + sense RNA then 4. RNA is translated into protein

Question 17

how does a partially-double stranded DNA virus make protein?

Answer 17

eg, hep B 1. DNA is transcribed to + sense RNA then 2. this virus packs its own reverse transcriptase which, with reverse transcription turns RNA to DNA. then 3. DNA replicated then 4. DNA transcribed (again) to + sense RNA then 5. this RNA is translated to protein

Question 18

how are viral proteins made?

Answer 18

mostly follow the rules of eukaryotic translation (because viruses use same machinery): 1. contain a 5’ cap and poly A tail 2. splicing in the nucleus, then exported to cytoplasm 3. monocistronic (one mRNA=one protein) with initiation at first AUG

Question 19

what is splicing?

Answer 19

one way to generate mRNA used by most DNA viruses. way to maximize protein production with a small amount of viral genetic material. (3 mRNA transcribed to translate protein - all made from a bit of ds DNA). viral DNA transcribes and SPLICES little bits of its mRNA into the host mRNA segments

Question 20

What is a segmented RNA genome?

Answer 20

• one way to translate protein that occurs in in - sense RNA viruses.
• This is a segmented RNA genome of ~8 segments. each segment encodes one protein. (segments analogous to chromosomes)

Question 21

what is the ‘promoter’s’ role in translation?

Answer 21

• one way to translate protein that occurs in in - sense RNA viruses.
• promoter starts transcription.
• transcription using different promoters can make 3 sections of mRNA and thus, translate 3 proteins.

Question 22

what is protease’s role in translation?

Answer 22

• one Way to translate protein in + sense RNA.

- after 1 really long protein is made, it is cleaved by protease into smaller proteins

Question 23

How do most enveloped viruses leave the cell?

Answer 23

the bud through plasma membrane

Question 24

How do most naked viruses leave the cell?

Answer 24

most lyse the cell to get out

Question 25

How fast do viruses replicate during latency? what about chronic viral infection?

Answer 25

they don't replicate during latency. very low level production of viral progeny during chronic inf

Question 26

What's an abortive viral infection?

Answer 26

infection of a non permissive cell with no viral progeny produced but cell death due to viral products (e.g., HIV)

Question 27

can viral infx cause cancer?

Answer 27

yes, they can trigger oncogenic transformation

Question 28

how do viruses evade host innate and T cell defenses?

Answer 28

1. interfere with inferon activity 2. interfere with cytotoxic T lymphocyte killing. 3. evade MHC 1 antigen presentation

Question 29

How do viruses evade antibody-mediated killing?

Answer 29

antigenic drift: viruses change their surface protein escape antibody recognition of viral surface

Question 30

what's the difference between virulent and attenuated virus?

Answer 30

attenuated can replicate but can't cause disease. | virulent can replicate and cause disease.

Question 31

Do RNA viruses mutate more than DNA viruses?

Answer 31

yes. DNA viruses usually use host machinery which works pretty well relatively - results in less errors/mutations than RNA virus. also RNA virus replicates faster = more error-prone

Question 32

what is complementation?

Answer 32

improvements in 1 viral progeny when influenced by another "helper virus"

Question 33

what are Defective interfering particles?

Answer 33

can use vaccines or antiviral therapy to block (interfere with) a productive infection of a normal normal virus by outcompeting for resources in the infected cell

Question 34

what is phenotypic mixing?

Answer 34

can change tropism of virus

Question 35

what is recombination?

Answer 35

(template switching) leads to viral genetic diversity

Question 36

what is reassortment?

Answer 36

leads to new genetic combinations from reassortment of viral gene segments - these are expressed in different proteins on virus surface. happens pretty quickly - causes Antigenic shit - can lead to pandemics

Question 37

what is antigenic drift?

Answer 37

random mutations slowly change phenotype

Question 38

list the 5 ways to diagnose viral disease.

Answer 38

1. ID of virus in culture 2. microscopic ID directly in specimen 3. serologic procedures to detect a rise in antibody titer or IgM 4. detection of viral antigens in blood and body fluids 5. detection of viral nucleic acids in blood or the patient's cells

Question 39

What are a couple ways to use cell culture to ID virus:

Answer 39

1. virus-induced cytopathic effects (CPE) (infected or dying host cells) or neoplastic cells

Question 40

What are a couple ways to use microscopy to ID virus:

Answer 40

1. look for cytopathic effects (CPE) using biopsied tissues or scrapings 2. fluorescent antibodies 3. electron microscopy

Question 41

What are a couple ways to use antibody titer or IgM to ID virus:

Answer 41

1. first IgM spike then IgG. second response to virus causes faster response from both but only IgG response has higher amplitude and lasts longer. 2. ELISA detects IgM, IgG or total Ab in blood 3. complement fixation - looks for antibodies

Question 42

What are a couple ways to use detection of viral antigens in blood or body fluids to ID virus:

Answer 42

1. radio immunoassay - sensitive for antigens but exposes lab personnel to radioactivity 2. ELISA "sandwich" to detect antigens 3. Competitive ELISA 4. Hemagglutinin (viral protein involved in attachment to respiratory cells - also agglutinates RBC in vitro - virus-specific antibodies interfere with the interaction between hemaglutinin on the virus and the RBC

Question 43

What are a couple ways to use detection of viral nucleic acids in blood or the patient's cell to ID virus:

Answer 43

1. DNA probes 2. PCR - amplifies DNA segments 3. Reverse transcription PCR for RNA templates

Question 44

how do naked viruses enter host cell?

Answer 44

endocytosis (viroplexis)

Question 45

how do enveloped viruses enter host cell?

Answer 45

endocytosis (viroplexis) and direct fusion (only enveloped viruses do this)

Question 46

how do + sense RNA viruses replicate themselves.

Answer 46

1. RNA directly translated after getting in cell (RNA polymerase made during this step). 2. This RNA polymerase used to make - sense strand 3. negative sense strand used as template to make a bunch of + sense strand copies for release.

Question 47

how do - sense RNA viruses replicate themselves.

Answer 47

1. these bring their own RNA polymerase with them and enter the cell. 2. using RNA polymerase, - sense strand transcribed to mRNA. 3. mRNA translated into proteins 4. using RNA polymerase, - sense strand is transcribed into + sense. 5. +sense is template for negative sense strand replication