Viruses Part II Flashcards
Replication sites of DNA vs RNA viruses in animal cells
DNA viruses replicated in the nucleus, RNA viruses replicated in the cytoplasm
Herpes virus example
Type: Genome: dsDNA
Penetration: enveloped virus enters via fusion with cytoplasmic membrane, nucleocapsid is transported to nucleus for uncoating
Transcription/translation:
- early proteins (necessary for transcription)
- delayed early proteins: viral specific DNA polymerase
- late proteins: nucleocapsid synth
Assembly and budding via nuclear membrane
- secretion via ER-golgi pathway
Polio virus and Hepatitis A virus
Type: RNA Genome Plus Strand
Genome can be directly translated –> large polyprotein which can be cut up into smaller proteins
- including RNA replicase to replicate minus strand to replicate more plus strands for the host to translate
Paralytic polio in 1% of the cases –> skeletal deformities caused by muscles ceasing to function (use of iron lung back in the day)
SARS CoV-2 mechanism
Type: Plus strand mRNA virus - unpacked in cytoplasm
Direct translation: Full length mRNA contains polymerase and necessary proteins for transcription into smaller portions
Virion does not need to bring its own proteins
How mRNA vaccines work
Vaccine contains mRNA piece for the cell to produce spike proteins which body responds to by developing antibodies against the virus
People had concerns the RNA would get incorporated into DNA which is impossible
Measles, Rabies (Rhabdovirus), Influenza (Orthomyxovirus) mechanism
Type: Minus strand RNA virus
Virion must contain RNA polymerase to transcribe minus strand –> plus strand RNA
- this cannot be done by host cell
mRNA produce by viral RNA polymerase and host machinery used to translate viral proteins
Measles overview
Severe complications: pneumonia, encephalitis, death
Long term complications: subacute sclerosing panencephalitis (SSPE) - fatal neurodegenerative disease
On the rise
Rotavirus
AKA Reovirus
- Causes gastrointestinal infection causing diarrhea
Type: dsRNA virus
Cannot be translated:
1) First must synthesize plus strand RNA using viral RNA-dependent RNA polymerase using minus strand as template
2) Plus strand is translated into proteins + minus strand for more dsRNA genomes
HIV and Rous sarcoma virus
Type: RNA retrovirus
Virion includes: 2 plus strand ssRNA, reverse transcriptase, integrase and proteases
Reverse transcriptase synthesizes ssRNA –> ssDNA –> dsDNA which is then incorporated into host genome as Provirus
- contains long term repeats (LTR) which help with integration and promote transcription
No excision possible in animal viruses
Two types of ssRNA plus strand viruses
Directly translation into mRNA
- SARS CoV2
OR by reverse transcription
- HIV
General consequences of viral infections in animal cells
Transformation into tumor cells
Fusion of cells - enveloped viruses can fuse with host cells and make heterokaryon
- contain hybrid cells and usually contain short-lived chromosomal abberations
Lysis (tissue damage)
Persistent infection - slow release of virus without cell death
Latent infection - can go on to lytic phase
Viral infections cause cancer how
Transformation of infected host cell into a tumor cell with uncontrolled replication
Can be caused by DNA and RNA viruses such as: Epstein Barr virus and Human Papillomavirus (DNA), Human T-lymphotrophiic virus (retrovirus), hepatitis B + C (RNA virus)
- 15-20% of all cancer
Mechanism: expression of viral protein induces transformation
Cancer mechanism via expression of viral protein
DNA viruses - may involve integration into host DNA or as a persisten extrachromosomal episome
Non-permissive hosts: non-replicating cells preventing virus from completing replication cycle - virus turns on mechanism for replication in cells
- Usually cells die as a result of this but only can become cancerous if the cells don’t die
Ex. HPV
HPV mechanism of lesion and cancer growth
Junctions in epithelium make basal epithelium vulnerable as it is the actively replicating layer
Nuclei with viral episome carries proteins which induce replication more than normal to form lesions
- viral production is not fast enough to kill cells
Viral genome is incorporated and replication becomes uncontrolled
- Can’t make the mechanisms to kill the cell
- Replication continues without cell death leading to invasive cancer
Anti viral drugs and types
Many anti-viral drugs target host structures causing toxicity and may not justify use
Nucleoside analogs can block reverse transcriptase or RNA dependent RNA polymerase in RNA viruses (AZT, Acyclovir, Malnupiravir)
Protease inhibitors: inhibit processing of large viral proteins into effective components
- ex. Paxlovid and for other + strand RNA viruses
Fusion inhibitors: prevents virus fusion with host cells
