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life cycle and antiviral effect. Major steps . Recognition Attachment Penetration Uncoating Early protein synthesis Nucleic acid synthesis Late protein synthesis Assembly Release. Attachment/Adsorption.

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major steps
Major steps
  • Recognition
  • Attachment
  • Penetration
  • Uncoating
  • Early protein synthesis
  • Nucleic acid synthesis
  • Late protein synthesis
  • Assembly
  • Release
attachment adsorption
Attachment/Adsorption
  • Virus attachment is through temperature independent ionic interaction
  • VAPs recognize specific receptors on the cell surface
  • Cells without the appropriate receptors are not susceptible to the virus.
penetration
Penetration:

An energy-dependent process, and the cell must be metabolically active for the penettration

  • Three main mechanisms are involved:

1)Translocation of the entire virus particle across the plasma membrane.

2) Endocytosis of the virus into intracellular vesicles (endosomes).

3) Fusion of the virus envelope with a cellular membrane.

uncoating
Uncoating
  • Uncoating is a process that viral capsid is degraded by viral enzymes or host enzymes
  • Some examples of uncoating
    • Pore formation: Picornavirus
    • Plasma membrane fusion:
    • Direct uncoating: paramyxoviridae
    • Partial uncoating: Hiv
    • Endosomal fusion: influenza virus
    • Endosomallysis: adenovirus
replication synthesis
Replication/synthesis
  • Replication involves assembly of viral proteins and genetic materials produced in the host cell.
  • begins immediately after the process of uncoating. The synthesis stage leads to the massive production of viral components.
  • involves transcription and the use of host ribosome to translate the viral mRNA into viral proteins. However, the strategies employed are different for different viruses.
replication synthesis1
Replication/synthesis
  • The important stages in the synthesis of various viral genome syntheses are :
  • dsDNA(+/-) Class I
  • ssDNA(+) dsDNA intermediate Class II
  • dsRNA(+/-) Class III
  • ssRNA(+) class IV
  • ssRNA(-) class V
  • ssRNA(+) DNA intermediate class VI
  • dsDNA (+/-) RNA intermediate class VII
release
Release
  • The last stage of virus replication cycle. Thousands of newly formed virus progeny leave the host cell in search of a new host cell, thus establishing an infection in the body.

Release includes:

  • Process
  • Lysis
  • Budding
    • At the plasma membrane
      • HIV assembly
      • Influenza assembly
    • At membrane of the cell organelles like endoplasmic reticulum (ER) or golgi apparatus
    • Synthesis and glycosylation of envelope proteins
  • Cell-cell fusion
viral attachment n entry
VIRAL ATTACHMENT N ENTRY

enfuvirtide(HIV):

  • works by disrupting the HIV-1 molecular machinery at final stage of fusion with target cell, preventing uninfected cells from becoming infected. Mimics components of the HIV-1 fusion machinery and displaces them, preventing normal fusion. Also called fusion inhibitors.
  • maraviroc(HIV): an entry inhibitor,blocks gp120 (V3 loop), which normally associates with the chemokine receptor CCR5. HIV is then unable to bind and enter human macrophages. Because HIV can also use another coreceptor, CXCR4, an HIV tropism test such as a trofile assay must be performed to determine if the drug will be effective.
slide11

docosanol(HSV): by inhibiting the fusion of the human host cell with the viral envelope of the herpes virus, thus preventing its replication. This mechanism has neither been directly observed nor proven, however.

  • The drug was licensed as an oral herpes medicine after clinical trials by the FDA in July 2000.[6] It was shown to shorten the healing by 17.5 hours on average (95% confidence interval: 2 to 22 hours) in a placebo-controlled trial.[7] Three other trials showed negative results, but these were not published.[
penetration1
PENETRATION
  • Interferon alpha:The IFN-α proteins are produced by leukocytes. They are mainly involved in innate immune response against viral infection. They come in 14 subtypes that are called IFNA1, IFNA2, IFNA4, IFNA5, IFNA6, IFNA7, IFNA8, IFNA10, IFNA13, IFNA14, IFNA16, IFNA17, IFNA21. These genes for these IFN-α molecules are found together in a cluster on chromosome 9.

IFN-α is also made synthetically as medication.

Types are:

  • Pegylated interferon alfa-2a
  • Pegylated interferon alfa-2b
uncoating1
UNCOATING
  • Amantadine(influenza):The mechanism of Amantadine's antiviral activity involves interference with a viral protein, M2 (an ion channel),[17][18] which is required for the viral particle to become "uncoated" once taken inside a cell by endocytosis
  • rimantadine(influenza):Rimantadine inhibits influenza's viral replication, by preventing the uncoating of the virus's protective shells, which are the envelope and capsid.
nucleic acid synthesis
NUCLEIC ACID SYNTHESIS
  • NRTIs(HIV):When HIV infects a cell, reverse transcriptase copies the viral single stranded RNA genome into a double-stranded viral DNA. The viral DNA is then integrated into the host chromosomal DNA, which then allows host cellular processes, such as transcription and translation to reproduce the virus. RTIs block reverse transcriptase's enzymatic function and prevent completion of synthesis of the double-stranded viral DNA, thus preventing HIV from multiplying.
  • A similar process occurs with other types of viruses. The hepatitis B virus, for example, carries its genetic material in the form of DNA, and employs a RNA-dependent DNA polymerase to replicate. Some of the same compounds used as RTIs can also block HBV replication; when used in this way they are referred to as polymerase inhibitors
slide16

foscarnet(CMV):Foscarnet is a structural mimic of the anion pyrophosphate[4] that selectively inhibits the pyrophosphate binding site[citation needed] on viral DNA polymerases at concentrations that do not affect human DNA polymerases. Because foscarnet is not activated by viral kinases it maintains activity against viruses like HSV and VZV that have respectively developed mutant thymidinekinase and UL97 encoded protein kinase, to gain resistance to other DNA polymerase inhibtors, like acyclovir and ganciclovir. Therefore, foscarnet is often used in acyclovir- or ganciclovir-resistant disease.

late protein synthesis and processing
LATE PROTEIN SYNTHESIS AND PROCESSING
  • protease inhibitors(HIV):used to treat or prevent infection by viruses, including HIV and Hepatitis C. PIs prevent viral replication by inhibiting the activity of proteases, e.g.HIV-1 protease, enzymes used by the viruses to cleave nascent proteins for final assembly of new virons.
viral release
VIRAL RELEASE
  • neuraminidase inhibitors(influenza): Neuraminidase inhibitors are a class of antiviral drugs targeted at the influenza virus, which work by blocking the function of the viral neuraminidase protein, thus preventing the virus from reproducing by budding from the host cell.
  • Oseltamivir (Tamiflu) a prodrug, Zanamivir (Relenza) and Peramivir belong to this class. Unlike the M2 inhibitors, which work only against the influenza A, neuraminidase inhibitors act against both influenza A and influenza B.