Lecture 6

Question 1

What are 3 qualities of living cells that viruses posses?

Answer 1

1) replicate
2) mutate
3) recombine

Question 2

Why are viruses not cells?

Answer 2

1) depend on cells to reproduce
2) don’t contain ribosomes so they can’t make proteins independently

Question 3

What are viruses that infect bacteria called?

Answer 3

phages

Question 4

What are the 2 viral life cycles?

Answer 4

lytic or lysogenic

Question 5

How does the lysogenic cycle work?

Answer 5

host cell doesn’t die and the virus or phage is transmitted to daughter cells

Question 6

Why cycle contributes to genetic diversity to the host?

Answer 6

lysogenic, adds new traits/DNA

Question 7

How do viruses differ? (4)

Answer 7

1) size
2) shape
3) genetic makeup (ssDNA, dsDNA, ssRNA, dsRNA)
4) shell structure (enveloped vs non-enveloped)

Question 8

What is the basic structure of a virus?

Answer 8

nucleic acids within a protein shell capsid

Question 9

What is the capsid made of? shapes? special quality?

Answer 9

capsomers

shapes: icosahedron or helical

can self assemble

Question 10

Structure of capsid assembly?

Answer 10

capsomers are asymmetric,
3 in each face and 20 faces per virion for icosahedral

Question 11

What is the capsid surrounded by in enveloped viruses? where do they get these components?

Answer 11

lipid-carbohydrate-protein envelope

lipid and carbohydrates = host membranes
proteins = virus

Question 12

What is the purpose of spikes?

Answer 12

attachment to host cells

Question 13

How do pages insert their nucleic acids?

Answer 13

tail fiber and base plate attache to host by binding to LPS and outer membrane porins. Inner tubes is released and the tip proteins degrade peptidoglycan and then it can insert nucleic acids

Question 14

Can viruses be classified by 16S rRNA?

Answer 14

nope, they don’t have it

Question 15

How can viruses be grouped?

Answer 15

host, nucleic acid composition, and envelope structure

Question 16

what are poxviruses labeled as?

Answer 16

complex bc the intricacy of their envelope

Question 17

What are the 5 steps of the viral life cycle?

Answer 17

1) attachment
2) entry
3) uncoating
4) viral gene expression and replication
5) assembly and release

Question 18

What is adsorption? why does it require (2)?

Answer 18

when virus stick, requires specific ionic and pH conditions

Question 19

What is tethering?

Answer 19

viral surface ligands can bind specifically and tightly to receptors on host cell

Question 20

What is trophism?

Answer 20

affinity for attachment to a specific tissue

Question 21

How do viruses enter?

Answer 21

enveloped = fuse with host cell membrane or endocytosis

non-enveloped = directly penetrate cell membrane or endocytosis

Question 22

What is uncoating?

Answer 22

once virus is in host cell it loses their capsid

Question 23

When do phages uncoat?

Answer 23

while entering the host cell

Question 24

What is replication?

Answer 24

making more DNA from DNA

Question 25

What is transcription?

Answer 25

making RNA from DNA

Question 26

What is translation?

Answer 26

making protein from mRNA

Question 27

How do viruses defy the central dogma?

Answer 27

replicating RNA and making DNA —-reverse transcription

Question 28

What type of sense mRNA do all viruses make?

Answer 28

+sense mRNA

Question 29

How do DNA viruses generate mRNA?

Answer 29

ddDNA: genomes transcribed by host RNA polymerase
ssDNA: host DNA polymerase produces missing strand

Question 30

How do RNA viruses generate mRNA? what enzyme does it require?

Answer 30

+strand of dsRNA and some +strand ssRNA directly translate, requires RNA replicase

Question 31

What do -strand RNA viruses have to carry?

Answer 31

preformed RNA replicase to make +RNA

Question 32

How do retroviruses work?

Answer 32

integrate into the host genome (lysogeny)

Question 33

How does HIV work?

Answer 33

prepackaged reverse transcriptase converts viral =RNA to DNA

Question 34

How does dsDNA integrate?

Answer 34

integrase which is carried within the virion

Question 35

How can viruses be release?

Answer 35

exocytosis = no cellular damage
lysis = cell bursts

Question 36

How can you measure viral growth in the lab?

Answer 36

plaque assay

Question 37

How does a plaque assay work?

Answer 37

1) mix culture of sensitive bacteria with phage
2) plate mixture on agar plate
3) after few hrs clear spots will appear
4) clearings (plaques) show where bacteria lysed by phage
5) count number of plaques (pfu) to find initial number of virions