Lecture 12

Question 1

permissive cell

Answer 1

allow for productive virus replication

Question 2

resistant cell

Answer 2

does not express the virus receptor

Question 3

movement of large protein complexes will not occur by diffusion because

Answer 3

the cytoplasm is crowded

Question 4

membrane fusion is regulated by

Answer 4

viral fusogens, (enveloped glycoproteins)

Question 5

fusion is highly _____

Answer 5

regulated

Question 6

what are the appropriate conditions for fusion

Answer 6

• lower pH: plasma membrane (pH 7) or an endosomal membrane (pH 5-6)
• binding to a second protein co-receptor (on plasma membrane or endosomal)
• proteolytic cleavage (activates fusion protein)

Question 7

fusion at the plasma membrane examples

Answer 7

sendai: viral attachment protein binds to receptor to stimulate a change and simulate a fusion peptide
HIV: viral attachment protein, interacts with receptor for HIV, binds to CCR and stimulates a change to push the fusion peptide in

Question 8

fusion at an endosomal membrane

Answer 8

• virions enter by endocytosis
• acidification changes conformation of VAP (low pH)
• reveals a hydrophobic fusion peptide
• fusion peptide penetrates host membrane
• further conformational change fuses membranes

Question 9

what viruses are already on the “right side” of the membrane

Answer 9

enveloped viruses

Question 10

how does a non-enveloped virus cross a membrane

Answer 10

makes a hole

Question 11

how does a non-enveloped virus make a hole through the membrane

Answer 11

conformational changes in the capsid expose something hydrophobic: hydrophobic amino acid sequence, fatty acid

Question 12

conformational changes can be due to

Answer 12

binding receptors, proteolysis, pH changes, etc

Question 13

what promotes membrane reorganization

Answer 13

hydrophobic domains from viral fusogen

Question 14

what is membrane reorganization

Answer 14

pore formation, membrane dissolution, usually use receptor-mediated endocytosis leading to endosomes

Question 15

poliovirus (non-enveloped) makes what size holes

Answer 15

small

Question 16

adenovirus (enveloped) makes what size hole

Answer 16

large

Question 17

poliovirus entry

Answer 17

-binds to its receptors
-conformational change reveals myristic acid
-myristic acid is ejected into membrane and disrupts the membrane
-allows hydrophobic amino acid residues to penetrate membrane
-creates a small pore in membrane
-the +ssRNA genome is injected directly into cytoplasm

Question 18

adenovirus entry

Answer 18

-initial binding to CAR by adenovirus fiber
-secondary binding to integrin
-acidification in endosome degrades capsid
-protein VI penetrates endosomal membrane
-membrane disruption allows remaining capsid to associate with microtubules and traffic nucleus

Question 19

viral polymerases

Answer 19

transcription and genome replication

Question 20

RNA viruses

Answer 20

-replicate in cytoplasm
-virus must use a viral polymerase
-viral RdRP generates both mRNA and new viral genomes
- +RNA virus must make a RdRP before any other transcription
- -RNA must package a RdRP in the virions

Question 21

DNA viruses

Answer 21

-replicate in the nucleus
-use Pol II to transcribe mRNA
-use host DNA-dependent DNA polymerases to replicate their genome
-drive cell cycle to S-phase
-replication is divided into early and late genome replication

Question 22

leaky scanning

Answer 22

-viral mRNA have start codons, can have poor Kozak consensus sequence
-scanning small ribosome subunit can sometimes miss these AUGs
-eg. Paramyxoviridae (measles)

Question 23

polyprotein synthesis

Answer 23

-entire viral genome is translated as a giant protein
-viral proteases self-cleave out and further process the genome
-eg. Picornaviridae (polio), Coronaviridae (SARS)

Question 24

why are virus particles built from sub-assemblies

Answer 24

ensures orderly formation and concentration dependent formation of viral particles

Question 25

how are virus particles built from sub-assemblies

Answer 25

formation of discrete intermediate structures P1 cleaved to capsid proteins VP1, VP3, and VP0 these proteins assemble into pentamers which can form empty capsids packaging of genome and cleavage of VP0 to VP2 and VP4 by a viral protease locks the capsid

Question 26

virus assembly occurs in

Answer 26

concentrated viral factories that are often visible by like microscopy

Question 27

viruses concentrate ______

Answer 27

proteins

Question 28

assembly and egress

Answer 28

acquiring an envelope virus can acquire a membrane from cellular membranes, often the plasma membrane viral glycoproteins accumulate on plasma membrane recruit other viral proteins and the viral genome (matrix and nucleocapsid) virion buds from surface

Question 29

virions can also acquire envelopes from

Answer 29

anywhere in the secretory system

Question 30

some virions require ______

Answer 30

maturation APUTTGAR(M)

Question 31

maturation

Answer 31

proper maturation is required for virion infectivity in some viruses e.g. HIV Gag polyprotein cleavage is prevented by protease inhibitors (Antivirals)