Virology Flashcards
(26 cards)
What are the smallest infectious agents?
Their genome consists of______and it is encased in__________ which is surrounded by a _________
Require ___ to replicate themselves aka _______
- Viruses
- RNA or DNA (double or single stranded), a protein shelf, which is surrounded by a lipid containing membrane
- require host machinery to replicate themselves AKA Obligate intracellular organisms
Viruses DO NOT 1.\_\_ 2.\_\_ 3.\_\_ 4.\_\_\_ Viruses DO 1. ?
Do NOT respire, grow, move or display irritability
Viruses DO REPLICATE, Evolve (breed true) and are independent
Virus outside capsid can be ___ or ___
naked or enveloped (lipids and glycoproteins)
What must be done for a negative sense stranded virus to be translated?
Negative sense viruses must transcribe negative strand into positive.
The virion brings its own or RNA dependent RNA polymerase
Positive sense means that the RNA is ready to be translated by host ribosome into protein.
Viruses can be classified by size, shape and type of nucleic acid; what are the types of NA?
Double stranded DNA (Herpesviruses, Adenoviruses, Poxviruses)
ss DNA (Parvoviruses)
ss (+) RNA (picornaviruses, togaviruses)
ss (-) RNA (myxoviruses, rhabdoviruses)
Retroviruses (ss (+) RNA to DNA) – HIV
ds RNA (reoviruses, birnaviruses)
ds DNA with RNA intermediate (hepadnaviruses)
RNA vs DNA viruses
Know
RNA VIRUSES
-Either positive sense or negative sense
- All RNA viruses except reoviridae are single stranded RNA (ss RNA)
- All replicate in the cytoplasm except influenza virus and retroviruses
DNA viruses
Most DNA viruses have both positive and negative sense strand
All DNA viruses except for parvoviridae are double-stranded DNA (ds DNA)
All replicate in the nucleus except pox virus
DNA VIRUSES
Don’t need to know
- Herpesvirus
DS and linear
Envelope
Herpes Simplex virus, varicella zoster virus (chicken pox), Epstein-barr virus (mono), Cytomegalovirus - Hepadnavirus
DS and circular
Envelope
Hepatitis B virus (acute and chronic hepatitis and an increased risk of hepatic fibrosis and carcinoma.)
3.Poxvirus DS and circular Envelope Smallpox virus ***does not replicate in the nucleus
4.Parvovirus
**SS and linear
No Envelope
Parvovirus B19
5.Papilloma virus
DS and circular
No Envelope
Human papillomavirus (HPV)
6.Adenovirus
DS and linear
No Envelope
Adenovirus
- Polyomavirus
DS and circular
No Envelope
JC virus, BK virus
RNA VIRUSES (WITH NO ENVELOPE)
Don’t need to know
1.Reoviruses
DS and linear
Rotavirus
- Picornviruses
SS + circular
Poliovirus, coxsackie virus,
rhinovirus
3.Hepevirus
SS + circular
Hepatitis E virus
4.Calcivirus
SS + circular
Norovirus
RNA VIRUSES (WITH ENVELOPE)
Don’t need to know
1.Flavivirus
SS + circular
West Nile, Dengue, Zika, yellow fever
- Togavirus
SS + circular
Rubella
3.Retrovirus
SS + linear 2 copies
Human immunodeficiency virus, HTLV-1
4.Coronavirus
SS + linear
Common cold, SARS, MERS
5.Orthomyxovirus
SS – linear, segmented
Influenza virus
6.Paramyxovirus
SS - linear, non segmented
Respiratory syncytial virus
7.Rhabdovirus
SS - linear
Rabies
8.Filovirus
SS - linear
Ebola/Marbug virus
9.Arenavirus
SS + & -, circular
Lymphocytic choriomeningitis virus
10.Bunyavirus
SS - circular
Hantavirus
11.Delta virus
SS - circular
Hepatitis D virus (requires hepatitis B DNA to replicate)
Viral Lifecycle
Attachment–>Penetration–> uncoating–> replication + transcription+ translation–> assembly / maturation–> Release
Fusion and entry of enveloped virus
attachment to cell-surface receptors–> penetration of membrane by FUSION PROTEIN –> merging of the viral envelope and cell membrane
What occurs after endocytosis of virus AND where does VIRAL RNA Replication occur
the genetic material is released from the capsid into the nucleus or cytoplasm
-RNA viruses undergo transcription, translation and replication in the CYTOPLASM
+ stranded RNAs are equivalent to messenger RNA. With the use of host ribosome the + RNA is converted into RNA dependent RNA polymerase to make copies of negative sense RNA.
Negative stranded RNAs will need to convert to + stranded copies by using viral RNA depended RNA polymerase.
Double stranded must break up DS into a single positive strand
VIRAL DNA REPLICATION
DNA viruses undergo transcription, translation and replication in the NUCLEUS
The viral transcription is divided into
a) immediate early,
b) early,
c) late transcription.
DNA are
transcribed in the nucleus –> mRNA–> spliced, and processed–> mRNA moves to the ER for translation
ASSEMBLY AND RELEASE
Structural protein + genome –> helical or icosahedral virion–> released
Naked viruses:
cell lyse and release the virions OR the virions may be released by exocytosis OR reverse phagocytosis
Coating of naked virus by budding through the golgi apparatus, nuclear membrane, or cytoplasmic membrane–> Enveloped virus
What are acute and chronic viral infections vs latency
acute viral infections: when a virus first infects a susceptible host. These are usually self-limiting.
Chronic infections = replicating virus can be continuously detected; often at low levels; with mild or no clinical symptoms.
Latent infections= virus persists in an occult, hidden, or cryptic form most of the times
Herpes virus
- typically latent
- Herpes simplex virus enters the neurons and persists in a non-infectious state
THERE ARE 8 MEMBERS
herpes simplex virus 1
herpes simplex virus 2, varicella-zoster virus
Epstein-Barr virus
cytomegalovirus
Human herpesvirus-6
Human herpesvirus-7 and Kaposi’s sarcoma herpes virus.
Resolution refers to?
elimination of the virus and the cells harboring or replicating the virus
Immune response to viruses includes?
Innate humoral and cellular immune
Interferon and cytotoxic T-cell responses may have evolved primarily as antiviral defense mechanisms.
How can viruses cause cancer?
Some DNA viruses and retroviruses establish persistent infections that can also stimulate uncontrolled cell growth, causing TRANSFORMATION OR IMMORTALIZATION of the cell.
The transformed cells:
Continue their growth without senescence
Alterations in cell morphology and metabolism
Increased cell growth rate and sugar transport
Loss of cell-contact inhibition of growth
Mechanisms of cell immortalization by viruses
Activating or providing growth-stimulating genes
Removing the inherent braking mechanisms that limit DNA synthesis and cell growth
Preventing apoptosis
Providing or inducing growth-stimulating cytokines.
Several oncogenic DNA viruses integrate into the host cell chromosome.
Examples: Papillomavirus, Epstein-Barr virus.
Retroviruses encode oncogenic proteins. The overproduction or altered function of these oncogene products stimulates cell growth.
Example: Human T-cell lymphotropic virus 1
Acyclovir and Ganciclovir
Specific to herpes simplex and varicella zoster
Activated by phosphorylation:
1. VIRUS THYMIDINE KINASE phosphorylated acyclovir into
monophosphate
2. Host cell kinases convert monophosphate to diphosphate & triphosphate compounds.
3. Acyclovir triphosphate inhibits viral DNA synthesis by
- Competitive inhibition of DNA polymerase
- Incorporation into viral DNA strand, preventing lengthening and elongation
Nucleoside analogs (specific to viral thymidine kinase and not human, so only cells with virus are susceptible)
Act as prodrugs: not toxic –> converted to toxic drug by phosphorylation
Resistance developed by rapid genetic variability in viral TK gene
Cidofovir
Monophosphate nucleotide analogue
-Inhibits VIRAL DNA Pol.
(also human dna pol to a lesser extent)
-incorporates itself into viral DNA and inhibits VIRAL DNA SYNTHESIS
IT IS NOT PHOSPHORYLATED (activated) by VIRAL KINASE
Resistance due to viral gene UL54 (DNA pol catalytic subunit) mutations
Active against: Herpesviruses, adenoviruses, poxviruses (including the smallpox virus), and human papillomavirus
Foscarnet
Inorganic pyrophosphate (non-nucleoside DNA polymerase inhibitor)
Blocks the pyrophosphate binding site on viral DNA polymerases— inhibits DNA and RNA polymerase, and HIV reverse transcriptase
Foscarnet is not activated by viral protein kinases, making it useful in acyclovir- or ganciclovir-resistant HSV and CMV infections
HSV or CMV particles can develop mutant protein kinases (thymidine kinase or UL97 protein kinase, respectively) that confer resistance
HIV Envelope proteins
glycoprotein (gp)120
three gp41 molecules
gp120 binds CD4 receptor on target cell (helper T-cell)
After gp120 binds, changes its conformation– exposes gp41, which assists in fusion
