Ch. 6

Question 1

What are viruses?

Answer 1

Microbes that are nonliving. They are small, lack metabolic processes, rely on a host to make more viruses, and can infect any form of life. CANNOT REPRODUCE THEMSELVES

Question 2

How do viruses work?

Answer 2

Go into host cells and use their machinery to replicate, get nutrients, and survive. They are an obligate intracellular pathogen - live in host cell

Question 3

Virion

Answer 3

Single infectious viral particle. Goal is to make more of these. Protective protein capsid around the virion

Question 4

Capsid

Answer 4

Main part of the virus. Has a protein shell that protects and packages the virus’s genome; capsomeres (subunits of the capsid) often involved in antiviral drug development

Question 5

Viral envelope

Answer 5

Envelopes are gotten from the host membrane while nonenveloped arise from cell lysis (bursts)

Question 6

Viral spikes (peplomers)

Answer 6

Are on the outside of the capsid and may/may not have envelope around them. *hosts learn to recognize spikes to mount immune response. Spikes change through mutation/evolution

Question 7

Bacteriophages

Answer 7

Infect strictly bacteria

Question 8

Viral goal

Answer 8

Get to host, inject its genome, use host machinery to make viral proteins

Question 9

How is virus DNA transcribed?

Answer 9

DNA viruses use host RNA to transcribe virus DNA

Question 10

Why do most viruses have fewer than 300 genes?

Answer 10

Because they’re simple, just need genes for their capsid proteins, and no organelles

Question 11

Why do viruses have a faster rate of genomic change?

Answer 11

bc lots of virions are produced when host cells are infected and have very fast replication since not much genetic material to copy. RNA genomes evolve faster than DNA viruses bc DNA has proofreading mechanisms

Question 12

Attenuated strain

Answer 12

Stimulate an immune response. Don’t cause disease in a host with normal immune system and used in vaccines (inject host with it so body stimulates immune response and kills it and you don’t get sick)

Question 13

Beneficial mutations may allow the virus to:

Answer 13

Escape host immune system, broaden host range, become more infectious, expand tropism (type of cell/tissue that the virus can infect)

Question 14

Antigenic drift

Answer 14

Minor changes; allow virus to evade quick antibody response from host system -> they go unrecognized long enough that they can replicate and make more virions. Eventually the host system might recognize it and perform an immune response and make antibodies

Question 15

antigenic shift

Answer 15

major genetic reassortment; can lead to new viral strains w/ deleterious features; can be increased infectivity with expanded host range; host doesn’t have any residual immunity to it anymore; lead to pandemics

Question 16

Covid-19 similar to influenza

Answer 16

enveloped virus, ssRNA virus, encapsidated, has surface proteins (spikes)

Question 17

Covid-19 differences to influenza

Answer 17

has a genome, type of surface proteins, s-spike proteins, influenza = HA & NA

Question 18

how SARS-CoV-2 works?

Answer 18

S protein binds to host cell’s ACE2 receptor -> injects RNA into infected host cell -> uses host machinery to replicate genome -> new host cells -> released -> infect other host cells

Question 19

Pfizer and Moderna

Answer 19

mRNA vaxs; they code for the SPIKE proteins with lipid -> intramuscular injection -> no damage to the RNA bc of lipid coating -> immune systems notices it doesn’t recognize the spike so it will make antibodies so if you come across covid, your immune system recognizes it -> quicker response and recovery

Question 20

J&J vax

Answer 20

attenuated viral vectored vaccine; has been genetically modified to be replication deficient so it’s incapable of causing human infxn

Question 21

How are viruses grouped?

Answer 21

type of nucleic acid (DNA or RNA), capsid symmetry (helical, icosahedral, or complex), presence/absence of envelope genome architecture (ssDNA, ssRNA, etc.)

Question 22

host range

Answer 22

refers to a collection of species that a virus can infect. Ex: measles only infect humans

Question 23

tropism

Answer 23

refers to the tissues or cell specificity sue to viral surface factors

Question 24

broad tropism

Answer 24

infect many different tissues/cells

Question 25

narrow tropism

Answer 25

infect one or a few tissues/cell

Question 26

bacteriophage replication - lytic replication

Answer 26

1) attach: phage binds to bacterial cell 2) penetration: phage injects genome into the host 3) replication: protein synthesis makes phage parts and genome is replicated 4) assembly: genome packed into capsid and phage structures assembled 5) release: bacterial cell lyses and new phages are released

Question 27

bacteriophage replication - lysogenic replication

Answer 27

1) attach: phage binds to bacterial cell 2) penetration: phage injects genome into the host 3) replication: *Integration - phage DNA integrates into host genome, forming a prophage *cell division - host and phage genomes r copied b4 cell division. Multiple cells now carry the phage genome *Lytic cycle entered - phage may enter lytic cycle if host is stressed 4) assembly: genome packed into capsid and phage structures assembled 5) release: bacterial cell lyses and new phages are released

Question 28

animal virus replication - HIV example

Answer 28

1) attachment and penetration: HIV attaches to host cell and enters by fusion 2) uncoating - if it has an envelope 3) reverse transcription: Upon entry, HIV genome is reverse transcribed by viral reverse transcriptase to make DNA 4) viral integration: DNA version of the HIV genome integrates into the host genome to make a provirus 5) replication: provirus is transcribed to make viral genome and translated to make viral proteins 6) assembly 7) release: HIV provirus directs the production of new virions, which bud from the host cell

Question 29

acute nonpersistent infection

Answer 29

cleared out naturally.

Question 30

latent persistent infection

Answer 30

have flareups w periods of latency; during flareups, virions are shed and person experiences symptoms. Ex: HIV

Question 31

chronic persistent infection

Answer 31

builds up

Question 32

provirus

Answer 32

integration of viral genome into host cell; can remain silent for years; may not be exhibiting symptoms but can still pass it *difference not excised from genome like in lysogenic bacteriophages

Question 33

acute infections

Answer 33

viruses infect host cell and new virions are made

Question 34

persistent infections

Answer 34

viruses have replication strategies that allow them to avoid immune system clearance

Question 35

What can persistent infections lead to?

Answer 35

cancer = oncogenic *cause cancer by stimulating uncontrolled replication of cells or ignore cell death signals

Question 36

Why would we grow bacteriophages via plaque assay?

Answer 36

to develop vaxs and drugs to combat viruses

Question 37

Since animal viruses are much harder and more costly to grow, what can we use?

Answer 37

embryonic eggs or live animal hosts like rats

Question 38

viral titer

Answer 38

quantity of a virus present in a given sample

Question 39

Diagnostic testing

Answer 39

determine presence of certain viruses

Question 40

specificity

Answer 40

detect only the virus and does not produce a false negative. won’t say there is _ virus if _ virus is actually not the one being detected

Question 41

sensitivity

Answer 41

test detects v low levels of the target *no false negatives / will detect _ target bc even just a little small level of _ target will be detected

Question 42

agglutination tests

Answer 42

clumping

Question 43

ELISA

Answer 43

detects antigens or abys in a sample *color change indicates binding

Question 44

Limitations of ELISA and agglutination assays:

Answer 44

cannot detect if antigenic shift occurs, takes time to build up abys to be detected

Question 45

PCR (polymerase chain reaction)

Answer 45

amplify a region of interest in the genome so that there's large amounts of it to use for further testing

Question 46

antiviral drugs

Answer 46

treat infections but don't typically cure them

Question 47

What do antiviral drugs target?

Answer 47

any part of viral replication

Question 48

difficulties in treating viral infections?

Answer 48

can be hard to reach them because they're in a cell

Question 49

prions

Answer 49

infectious proteins, nonliving, do not replicate, acellular, no genetic material. only way to ID is by autopsy. Causes transmissible spongiform encephalopathies (TSEs) sponge like holes in brain tissue

Question 50

what should antivirals be?

Answer 50

selectively toxic.*U don’t wanna kill too many host cells, need balance

Question 51

what can we do to prevent infections?

Answer 51

vaccinations