Virology Lecture 4

Front 1

what occurs during viral biosynthesis?

Back 1

generate mRNA, translate mRNA to generate protein, replicate viral nucleic acid

Front 2

what does the term 'replicate' mean in terms of viral nucleic acid?

Back 2

exact copies of viral genomes (directly or through intermediate copy)

Front 3

what do DNA viruses use to replicate?

Back 3

most use viral and cell factors

Front 4

what do RNA viruses use to replicate?

Back 4

all use viral polymerase, some use additional cell factors

Front 5

why do RNA viruses all use viral polymerase?

Back 5

there are no cellular RNA-dependent RNA polymerase or general RNA-dependent DNA polymerase (telomerase is a special case)

Front 6

what types of antiviral agents would affect viral replication?

Back 6

nucleotide analogs that inhibit viral component (but inhibit cell component minimally or not at all), non-nucleoside reverse transcriptase inhibitors

Front 7

how are retroviruses a special case in replication?

Back 7

use reverse transcriptase to copy genome to DNA, then integrase to insert DNA into cell's chormosomes, creating a permanent viral DNA copy in genome, so cell RNA polymerases transcribe integrated DNA just like cell DNA, cells can't be cured of these viruses

Front 8

what is reverse transcriptase?

Back 8

Viral RNA-dependent DNA polymerase

Front 9

what does reverse transcriptase do?

Back 9

copies RNA genome into DNA copy

Front 10

what is integrase?

Back 10

viral enzyme that cuts cell DNA and inserts viral DNA into cell chromosome

Front 11

what does integrase do?

Back 11

cuts cell DNA and inserts viral DNA into cell chromosome

Front 12

how do we cure retrovirus infected cells?

Back 12

can't, so focus on inhibitors of polymerase first

Front 13

what do nucleoside analogs do?

Back 13

inhibit polymerase

Front 14

nucleoside analogs inhibit polymerase by what mechanisms?

Back 14

chain terminators & polymerase inactivators

Front 15

what are examples of chain terminators?

Back 15

Azidothymidine (AZT) and Acyclovir

Front 16

what does AZT stand for?

Back 16

Azidothymidine

Front 17

what does AZT treat?

Back 17

HIV

Front 18

what does Acyclovir treat?

Back 18

genital herpes simplex virus (HSV) and varicella zoster (chicken pox/shingles)

Front 19

what mechanism, besides chain termination, does acyclovir work via?

Back 19

polymerase inactivator

Front 20

how do chain terminators work?

Back 20

DNA polymerase insterts nucleoside analog in growing DNA chain, but then that chain can't accept any more nucleotides (terminated)

Front 21

what is a nucleoside analog?

Back 21

ddNTP (dideoxyNTP)

Front 22

what is one problem with chain terminators?

Back 22

must insert early enough that functional mRNA isn't made (excess DNA is already trimmed off)

Front 23

how does AZT work?

Back 23

high affinity for HIV reverse transcriptase causing premature termination of HIV DNA chain while having a low affinity for cell DNA polymerase so low toxisty for cell DNA synthesis

Front 24

how do polymerase inactivators work?

Back 24

nucleoside analog is phosphorylated (by kinase) to generate NMP-analog which is phosphorylated to an NDP-analog, which is phosphorylated to an NTP-analog, which binds DNA polymerase irreversibly and therefore inactivates it

Front 25

what are the types of polymerase inactivators?

Back 25

cell kinase & viral kinase (which phosphorylate nucleoside analogs to nucleotide monophosphate (NMP)

Front 26

what is an example of a cell kinase chain terminator?

Back 26

Vidarabine (secondary to acyclovir) to treat HSV

Front 27

what is the problem of a cell kinase chain terminator?

Back 27

nucleoside analog will be converted to NTP in uninfected cells, which is toxic to the cell

Front 28

how do cell kinase chain terminators work for viral infections (vs cell damage?)

Back 28

the NTP-analog has a higher affinity for viral polymerase than cell polymerase, so better inactivator of viral polymerase

Front 29

what is an example of a viral kinase chain terminator?

Back 29

acyclovir (treat HSV, varicella zoster) & ganciclovir (cytomegalovirus)

Front 30

what is the advantage to viral kinase chain terminators over cell kinase chain terminators?

Back 30

nucleoside analog will be converted t oNTP only in infected cells

Front 31

how do viral kinase chain terminators work for viral infections (vs cell damage?)

Back 31

the NTP-analog has a higher affinity for viral polymerase than cell polymerase, so better inactivator of viral polymerase

Front 32

viral kinase chain terminators are describes as BLANK specific for viruses:

Back 32

doubly specific (viral kinase and viral polymerase)

Front 33

how can retrovirus replication be inhibited?

Back 33

inhibit viral polymerate using nucleoside analogs (chain terminators like AZT) & Non-nucleoside reverse transcriptase inhibitors (which binds RT and inhibits it) and inhibit viral integrase (Isentress-HIV integrase inhibitor which prevents integration of HIV DNA)

Front 34

what occurs in viral maturation & assembly?

Back 34

virion or nucleocapsid (if enveloped virus) is assembled from proteins and nucleic acid, and the envelope is genereally acquired during release

Front 35

what are the three mechanisms for viral release?

Back 35

cytolysis, budding, extrusion

Front 36

what occurs in cytolysis?

Back 36

cell dies & virus is released

Front 37

what are the types of cytolysis?

Back 37

necrosis and apoptosis

Front 38

what is necrosis?

Back 38

release of cell lysosomal enzymes (due to infection)

Front 39

what is apoptosis?

Back 39

activation of specific cell signal transduction pathway, for 'cell suicide'

Front 40

what type of viruses is budding restricted to?

Back 40

enveloped viruses only!

Front 41

what occurs during budding?

Back 41

nucleocapsid acquires envelope by budding through cell membrane (picks up viral proteins there); the location is virus specific (plasma membrane, nuclear membrane, golgi membrane) and then final release, it can pick up some cell proteins too, and does not necessarily kill the cell

Front 42

what common virus undergoes budding?

Back 42

influenza

Front 43

how does influenza undergo budding?

Back 43

viral hemagglutin (viral attachment protein) binds sialic acid (cell receptor), then viral neuraminidase cleaves sialic acid, freeing virus from cell membrane (critical for entry/exit)

Front 44

what occurs during extrusion?

Back 44

nonenveloped viruses extrude through membrane, but it is poorly understood

Front 45

how does a multinucleate syncytia form?

Back 45

newly synthesized viral fusion proteins at cell surface cause fusion of infected cell with neighboring uninfected cells

Front 46

what does a multinucleate syncytia allow?

Back 46

viruses to spread to other cells iwthout ever exposing themselves extracellularly

Front 47

what are the experimental and current anti-HIV strategies?

Back 47

block attachment (soluble CD4; not being done), block fusion (Fuzeon [v], Maraviroc [c]), inhibit RT (nucleoside analogs, NNRTI), inhibit integrase (Isentress), inhibit assembly

Front 48

what does HAART stand for?

Back 48

highly active antiretroviral therapy

Front 49

what does HAART mean?

Back 49

several drugs (typically 3-4) are taken in combination because simultaneous mutation in many viral genes is rare

Front 50

if an antiviral targets cellular paths/proteins, what are the affects on viruses and cells?

Back 50

viruses have a low frequency of mutation to drug resistance while cells may have normal funcitons intered with

Front 51

what is the cell response to viral replication?

Back 51

viral replication in cell induces immediate cell response (first defence, before immune response) and infection induces synthesis of interferon in cell (does nothing to virus, but induces other antiviral events)

Front 52

what does interferon do?

Back 52

induces antiviral events (does not directly do anything to virus)

Front 53

what types of interferon are there?

Back 53

alpha ('leukocyte' made in lymphoid cells), beta ('fibroblast' made in virtually all cells), and gamma ('immune' made in T & NK cells, potentiates alpha & beta interferons)

Front 54

what does interferon gamma do?

Back 54

potentiates alpha & beta interferons

Front 55

what does interferon beta do?

Back 55

protects neighboring cells by binding receptors on neighboring cells and inducing the cell to synthesize antiviral proteins which serves as a 'red flag' to warn surrounding cells (after production and secretion from infected cell)

Front 56

how do viruses inhibit the interferon system?

Back 56

inhibit the cell factors involved in making IFN and the cell factors involved in IFN making antivirals