viral replication

what are the drug targets for antiviral drugs?

1. nucleic acid polymerases

2. proteases

3. integrases

4. Neuraminidases

what will happen if a drug targets the nucleic acid polymerases of a virus?

the virus will be unable to synthesize new viral RNA or DNA, stopping the production of new viral genomes

what is an example of a virus that the drug targets the nucleic acid polymerases?

herpes

what will happen if the drug targets proteases of a virus?

individual proteins not created

what will happen if a drug targets the integrases of a virus?

enzymes of retrovirus will be unable to enter host

what is an example of viruses that the drug targets the neuraminidases of the virus?

1. parvovirus

2. influenza

what is an example of a virus that the drug targets the integrases?

1. FELV

2. FIP

what are the main uses of antiviral drugs?

1. ease symptoms

2. shorten length of infection

are antivirals curative of the viral infection?

no

what are the adverse effects of FIP antiviral GS-441524?

urinary bladder stones

FIP

fatal viral disease caused by a mutated feline coronavirus

how does FIP antiviral GS-441524 work as an antiviral (general steps)?

1. phosphorylation to form nucleoside

2. incorporation into viral DNA

3. termination of RNA chain inhibiting replication

what makes FIP antiviral GS-441524 cause urinary stones?

limited solubility of the drug

in what form do we study viral replication?

in vitro

in vitro

using a cell culture plate to study the virus

the increase in infectious virus is measured over time by...

sampling the virus in the supernatant

transcription

genome to mRNA

what are the two different sources and products for transcription?

1. DNA to RNA

2. RNA to RNA

translation

mRNA to protein

how does replication differ in viruses compared to eukaryotes?

in viruses we have both RNA and DNA but eukaryotes it is only DNA

what determines the order of transcription, translation, and replication in a virus?

1. DNA or RNA genome

2. postive or negative polarity (5-3' or 3-5')

positive sense RNA replication

1. nucleic acid can directly bind to ribosomes and start translating partially or fully

2. after translation the mRNA will code for their own viral polymerase to replicate their genome

3. enzyme produced after translation to carry out the RNA transcription and translation

negative sense RNA replication

viruses must carry their own polymerase enzyme into their nucleocapsid, a specific RNA-dependent RNA polymerase; they basically have to transcribe and translate to have a protein and not only a gene

how do we study viruses that do not grow in cell cultures?

we construct an infectious clone of the virus meaning we will insert the viral genome into a plasmid

what do we learn from entering an infectious clone into the virus?

researchers understand what host receptors are necessary for that specific viral cell type to enter and the promoters needed to start replication and transcription of the virus

viral attachment

receptors on the viral envelope or capsid become connected to complementary receptors or co-receptors on the cell membrane expressed by susceptible cells in the host

susceptible cell

virus can infect the host cell, but the virus will not complete their replication cycle

permissive cell

virus can infect the host cell and the virus will complete their replication cycle

how will naked viruses penetrate the host cell for entry?

endocytosis

why is entry into the host cell via endocytosis less advantagous for the virus?

will can an inflammation reaction alerting the immune system of an issue in the host cell

how will enveloped viruses penetrate the host cell for entry?

membrane fusion

what are the sequence of events of the one-step growth curve?

1. inoculation

2. eclipse

3. burst

4. burst size

viral uncoating

the viral capsid opens and frees the genome

what is required to move the virus within the cell and why?

viruses are non-motile particles so they will require a "chaperone" (cellular protein) to take viral genome to nucleus

what does it mean if the virus has partial signaling?

replication is occurring in capsid to avoid recognition of the virus by the immune system

where are packing sequences of viruses located?

located on end of viral genome

what is the packing sequence used for in the viral genome?

it allows the protein and genome virions to find each other; it allows the virus to enter the procapsid

eclipse time

period after the virus has penetrated the host cell; however, it cannot be observed for hours in the host until the first progeny of virions becomes visible again

what is eclipse time variable within?

families/genus

what is eclipse time constant in?

the families OR the genus

why is the eclipse time important when developing antiviral drugs?

when the virus has disassembled its capsid (protective coat) in order to replicate its genome and synthesize proteins; at this stage the virus is highly reliant on the host cell making it susceptible to drugs that inhibit replication, transcription or translation

incubation time

the time between the infection of the host until it shows clinical signs, all which occur in vivo

in vivo

in the host cell

what is eclipse time UNRELATED to?

inoculation time

what do DNA viruses that replicate in the nucleus use to produce their mRNAs?

cellular-dependent RNA polymerase

what do DNA viruses that replicate in the cytoplasm use to produce their mRNAs?

MUST carry a DNA-dependent RNA polymerase of their own

how do naked viruses exit the host cell?

cell lysis (bursting)

how do enveloped viruses exit the host cell?

budding or exocytosis

what are the basic steps of viral replication?

1. Attachment

2. Penetration

3. Uncoating

4. Transcription of early mRNA

5. Translation of early proteins

6. Replication of viral DNA

7. Transcription of late mRNA

8. Translation of late proteins

9. Assembly of virions

10. Release

why are antiviral drugs often not used in veterinary medicine?

cost and lack of information in safety and efficacy (not enough clinical trials performed)

who can antiviral drugs NOT be used in?

food animals

what are the preferred preventitive measures taken rather than using antivirals?

vaccination, biosecurity, and depopulation

what is important to know about the treatment of viral infections?

treated symptomatically (alleviate clinical signs) and palliatively (treat but not with the intent of curing)

what group of viruses have a genome that allows for the direct translation of proteins immediately upon uncoating?

viruses with positive RNA genome

2 multiple choice options

for cellular enzymes, what is required for DNA synthesis?

DNA polymerase

for cellular enzymes what is required for mRNA synthesis?

RNA polymerase

DNA polymerase produces

DNA

RNA polymerase produces

RNA

reverse transcriptase is important for

retroviruses

what does reverse transcriptase produce?

produces DNA from an RNA template

retroviruses have a..

2 copies of single stranded positive polarity RNA

how do retroviruses replicate

through a DNA intermediate that inserts into the host genome

in retroviruses the double stranded DNA will contain additional sequences called...

LTR (long terminal repeats)

why are LTRs important in retrovirus replication?

1. allows viral genome to integrate to host genome

2. act as a strong promotor

why do we want to target the LTR when creating antiviral drugs?

transcription of viral RNA and replication of the viral genome occur from this integrated (proviral) DNA

what is replication of retroviruses based on?

reverse transcription

why is it common to see side effects in antiviral drugs?

viruses use metabolic pathways of the host cell to replicate so inteferring with viral agents can be toxic to cell

how do analog drugs act against viruses?

will act as chain terminators and stop DNA or RNA polymerase from adding further nucleotides

acyclovir is an inhibitor of...

herpesvirus DNA polymerase

how is acyclovir delivered (form)?

prodrug

what does acyclovir require to transform to its active state?

tyrosine kinase to get phosphorylated to active state

what are adverse effects of acyclovir?

drug is non-toxic to uninfected cells since activation of drug only occurring in infected cells

what type of analogue is acyclovie?

purine analog, specifically guanosine

what does acyclovir do to infection?

reduce duration and severity of clinical signs; DOES NOT CURE HERPESVIRUS

what is the HIV drug an example of?

antiretroviral drug cocktail