Lecture 3

Question 1

Three essential steps in viral replication

Answer 1

1. Cell attachment and entry–> initiation of replication
2. Production of viral components
3. assembly and viral release

Question 2

What is multiplicity of infection

Answer 2

1 infectious virus/cell

Question 3

How to calculate plaque forming units (PFU/mL)

Answer 3

of plaques on plate/ volume of starting solution
or # of plaques on plate*dilution factor/volume plated

Question 4

Where is the best place to block viral infection

Answer 4

Initiation of replication
-virus doesn’t get into cell in first place

Question 5

How does virus do first step initiation of replication (attachment and replication)

Answer 5

Uses host cell receptors–>help attach
Receptors–>binding receptors changes conformation

Question 6

What 2 things do viruses like HIV need to penetrate via membrane fusion

Answer 6

1. Receptor->CD4
2. Co-receptor->CCR5 or CXCR4

Question 7

True or false: Immune cells with only 1 receptor are susceptible to virus infection

Answer 7

False: Immune cells with BOTH a receptor and co-receptor are susceptible to virus infection

Question 8

What does it mean for the virus to be metastable or spring loaded

Answer 8

Unlocks energetic state that allows for fusion occur

Question 9

How do enveloped viruses enter

Answer 9

Fuse through the membrane

Question 10

How do non-enveloped viruses enter

Answer 10

1.Make a hole through membrane and delivers genome to cytoplasm
2. Lysis/kills cell & releases viral particles

Question 11

What 2 ways can viruses enter?

Answer 11

1. Cytoplasm
2. Endocytosis

Question 12

How does low pH trigger viruses to enter through endocytosis?

Answer 12

-Low pH signals virus that it is inside an intracellular location & that it should start penetration before it gets killed by phagocytosis–>low pH means phagocytosis will happen
-Low pH causes to virus structure to become metastable–>causes fusion

Question 13

How does virus get to nucleus?

Answer 13

Viruses/viral components hitch rides around cell that leads to or close to nucleus by cytoskeletal network

Question 14

How does virus get through nuclear membrane

Answer 14

1. Waits for nuclear membrane to break down during cell division
2. Partially disassemble in cytoplasm at nuclear pore
3. Jam intact virion through nuclear pore

Question 15

What type of polymerase do hosts use?

Answer 15

DNA dependent RNA polymerase

Question 16

How do viruses make more than 1 protein?

Answer 16

1. Multiple transcripts
2. Alternative splicing
3. Alternate start codons

Question 17

How does a polymerase that keeps falling off make multiple proteins

Answer 17

A single polymerase will fall off and restart at each gene creating multiple proteins

Question 18

What does protease do?

Answer 18

Cuts large polyprotein into functional pieces
-important for viral replication

Question 19

Why is inhibiting/stopping protease a main target for (+) RNA & HIV?

Answer 19

Stopping/inhibiting porteases stops viral infection since it cant replicate anymore

Question 20

Does virus need more capsid or protein?

Answer 20

Capsid

Question 21

Can viruses run through stop codons

Answer 21

yes, they can go past stop codon
-rare but can make extra proteins