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Virology
Virology morphology
| Question | Answer |
|---|---|
| What is the avg size of a virus? | 20-300nm in diameter |
| Why are viruses filterable? | Because they pass through micropore filters |
| What are the 3 morphologies of viruses? | cubic, helical and complex |
| What type of viruses are ether sensitive? | enveloped |
| Why are viruses obligatory intracellular parasites? | because they have a limited genome and need the host cell’s hardware |
| Can viruses infect any type of host? | No, only permissive host. Not non-permissive |
| Why do some viruses need a helper virus? | because they are defective and require a co-infection |
| Where is the viral genome encoded into? | capsid |
| What is the capsid made of? | proteins called protomers or capsomeres, some viruses (e.g. HIV) derive from pro-peptides by protease activity How do you stop protease activity? |
| What is a nucleocapsid? | protein-nucleic acid complex |
| How are the capsid assembled in helical vs icosahedral symmetry? | by assembling the capsid on the nucleic acid vs independent of it the icosahedral (can cause defective virus) |
| Where can the envelope of a virus be derived from in a host? | cell membrane, nuclear env or golgi while “budding” out |
| What kinds of proteins are on the surface envelope of a virus? | glycoproteins |
| What is the function of glycoproteins? | They are viral attachment proteins (VAP’s) e.g. gp120 on virus bidns CD-4 receptors in TH cells |
| What are the 4 stages of cell infections? | 1. Recognition, 2. penetration, 3. uncoating, 4. synthesis and propagation |
| What is tropism? | tissue specificity in viral infections due to receptors |
| How do glycoproteins appear on the cell? | as spikes or peplomeres |
| How does ether act on envelopes? | it disrupts their lipid rich envelope |
| What are hemaggluttins (HA’s)? | (VAP) Viral attachment proteins that bind RBC’s |
| What do HA’s of orthomyxoviruses (influenza) bind? | the terminal sialic acid (neuramic), released by neuramidases |
| What are fusion inhibitors? | inhibit interaction of VAP’s with target cell |
| How do non-enveloped viruses penetrate the cell? | via receptor mediated endocytosis or viropexis, done by hydropobically permating through(slipping by) |
| How do enveloped viruses penetrate the cell? | By fusion, of viral envelope with the cell membrane |
| Where do RNA and DNA viruses replicate? | RNA in the cytoplasm and most DNA in the nucleus |
| Which DNA or RNA viruses are known as tumor viruses? | DNA= Herpesviridae(EBV- burkitts lymphoma), Papilomaviridae(papilloma virus – cervical cancer), poliomaviridae, adenoviridae, hepadnaviridae (HBV-hepatomas) and RNA = retroviridae (can cause tumor). |
| What are the 4 groups of RNA genome? | ss +ve sense (mRNA like, fast, no RNA-P), ss –ve (antisense, not fast, use as a template for +ve strand, uses viral RNA-P) dsRNA (segmented) viruses, retroviruses (2 copies of +ve ssRNA) |
| Which type of RNA functions as an mRNA? | +ve sense |
| Which RNA type does not contain RNA dependent RNAP and why? | +sense, because it is already used as an mRNA and it can make proteins |
| Which RNA type cannot infect when purified? | -ve sense RNA |
| Which RNA is there an mRNA capping | segmented dsDNA |
| What is reverese transcriptase? | RNA dependent DNA polymerase |
| What particles are packed in retroviruses? | Reverse transcriptase, RNase H, protease, integrase enzymes and ssRNA genome(2copies) |
| After RNA is copied to DNA the hybrid what does RNase H Do? | replace the other strand with DNA |
| What is a provirus? | In Retroviruses when the final form is obtained DNA-DNA strand |
| What do integrase enzymes do? | introduce retroviral DNA into the host DNA |
| Besides Retroviruses with oncologic genes, is there any other type of RNA virus capable of forming tumors? | yes, lentiviruses |
| What happens in DNA viruses? | Virus uncoats, dNA enters the nucleus, it is then transcribed to mRNA and viral proteins are made. |
| What do early genes in DNA viruses do? | transcribe regulatory proteins |
| What do late genes in DNA viruses do? | make proteins for replications and capsid packaging |
| What is an arbovirus? | it is acirus that has arthropod vectors such as mosquitoes or ticks to transmit to a vertebrate host |
| What are some arboviruses? | dengue, yellow fever, encephlatis |
| What are some of the families that the arboviruses belong to? | togaviridae, flaviviridae, bunyaviridae, rhabdoviridae, arenaviridae, reoviridae. |
| What are the 3 genes in arboviruses and wha they code for? | 1. gag - capsid, 2. pol – reverse transcriptase, Nuclease(RNaseH), integrase and protease, 3. env – envelope glycoproteins |
| What are prions made of? | Not viruses, it is a mutantprtoeins with particles made of a single protein, without nucleic acid. |
| What are prions resistant to? | Formaldehyde, heat, uv, nucleases and somewhat protease resistant |
| What do prions Do? | Create a wild type protein misfold |
| What is an amyloid? | Is when prions expose the hydrophobic part of protein causing it to agglutinate and pile up in the nerve cells. |
| What causes transmissible spongioform disease and why is it called that? | prions cause it and it is because the infected cells have a vacuolated appearance |
| What is the gene that causes the misfold, and what protein is made? | PrPc is the gene and PrPsc is the protein made |
| What animal is affected by scrapie? | sheep |
| What animal is affected by mad cow disease (bovine spongioform disease)? | Cattle |
| What animal is affected by Kuru and Creutzfeldt Jacob Disease ? | Humans |
| Where are viruses cultured? | in embryonated chicken eggs, primary cell cultures and permanent cell lines |
| Why are viruses cultured? | to make vaccines |
| Why do some people need to check for allergies to a vaccine? | chicken protein contaminants may be present and can trigger a reaction |
| What are methods of viral Quantitation and titration(physical methods)? | PCR, RIA, ELISA, electron microscopy |
| What are The biological methods of viral detection? | Animal death, infection, cytopathic effects including plaque assays |
| Whar are the cytopathic effects that help in virus detection? | presence of cell lysis, necrosis, syncytial formation, giant cell formation, inclusion formation, vacuolization |
| What is inclusion and how are they detected? | Inclusions are indicatory of rabies and they are detected by taking up eosin stain |
| How do you detect viral specific proteins? | by ELISA, RIA, Western Blot |
| How is influenza detected? | by a hemagluttinin assay |
| What does PCR help you detect? | virus-specific nucleic acid |
| What are the means of laboratory infection? | aerosols, ingestion, skin penetration and eye splashes |
| What are some methods of laboratory safety? | training aseptic techniques, no mouth pipetting, no eating/drinking/smoking in lab, protective gear, sterilization of wastes, hoods, immunizations, level 4 facility conatinent of high risk viruses(e.g. ebola and rabies). |
| What morphology of viruses is stable at 37C? | icosahedral |
| Are enveloped viruses more heat labile(change)? | Yes |
| Most viruses are inactivated at 50-60C except for? | Polyoma, HBV and prions |
| What temperature can most viruses be stored? | -80C |
| What temperature can viruses be lyophilized (dehydrated)? | at 4C or RT |
| What happens to enveloped viruses at 90C? | lose infectivity, and they are sensitive to freezing and thawing |
| What do salts do to viruses and how doe sit affect shelf life? | stabilizes them, for this reason why vaccine preparations contain salts to increase shelf life |
| What salt stabilizes picornaviruses and reoviruses? | MgCl2 |
| What salt stabilizes herpesviruses? | Na2SO4 |
| What pH are most viruses stable? | Between 5-9 |
| Are enteric viruses stable at low pH? | Yes |
| What does very high pH do to viruses? | kills all of them |
| What does UV light and y Radiation do to viruses? | inactivates them they can’t replicate |
| How does photodynamic inactivation work? | toluidine blue, neutral red or proflavine are absorbed by nucleic acids in the virus, making them sensitive to light |
| Which virus are feature of the virus makes them ether sensitive? | envelope |
| What detergents are used to inactivate enveloped and non-enveloped viruses? | enveloped = Nonidet (NP40) and Triton X-100. Non-enveloped= SDS |
| Why is formaldehyde a great inactivation agent for vaccines? | it interacts less with protein and does not reduce antigenicity, it attaches better to single strand than double strand nucleic acids |
| What is recombination? | viruses can interchange DNA to create a new mutant virus, lot of variability in segmented RNA (e.g. influenza) |
| What is complementation? | when 2 viruses on the same host cell can complement each other by transactivation |
| What is interference? | when one virus inhibits the replication of another in the same host |
| What virus could be used for gene transfer in mammalian cells for gene therapy? | retrovirus and certain DNA viruses(adenovirus) |
| Why retroviruses for gene therapy? | They have 2 copies and can permanently leave one in the host, used to replace defective genes, but the oncogenes need to be removed, the only down is that retrovirus may recombine with other viruses making it oncogenic |
| What is the major route of transmission of viruses? | aerosols and dropplets |
| What viruses are transmitted by aerosols and droplets | influenza, measles, smallpox etc. |
| What viruses are transmitted by fecal-oral route? | enteroviruses, polio, rotaviruses, HAV |
| What viruses are transmitted by sexual contact? | HBV, HSV2, HIV1 and 2 |
| What viruses are transmitted by hand-mouth/eye and mouth-mouth? | HSV1, EBV, Rhinovirus |
| What viruses are transmitted by blood exchange? | HIV, HBV |
| What viruses are transmitted by animal to animal with human as an accidental host? | rabies(dog), aerosols (rodents) arenaviruses and hantaviruses |
| What viruses are transmitted by arthropod vectors (e.g. mosquitos and fleas)? | arboviruses – togaviruses, flaviviruses and bunyaviruses |
| What is the transmission pattern of human-arthropod? | urban yellow fever, dengue |
| What is the transmission pattern of lower-vertebrate anthropod with tangential human infection? | Jungle yellow fever, st. Louis encephalitis |
| What is the transmission pattern of arthropod-arthropod with accidental human? | Colorado tick fever, LaCrose encephalitis |
| Why are arthropods a good vector? | because they are not affected in any way by the virus |
| What are the routes of entry for viruses? | Skin, GI, Respiratory tract, UG system or eye, fomites(needles) |
| What are the 2 most popular route of entry | respiratory tract and GI |
| Do some viruses only infect locally? | yes, e.g. influenza, parainfluenza only infects respiratory tract |
| How do some viruses spread systemically? | Via viremia or the lymphatic system |
| How can viruses replicate ate the point of entry ? | yes, and then they spread through the body including the CNS according to tropism |
| Can viruses remain latent in the body? Give an example? | yes, e.g. herpes remains latent in trigeminal ganglia or sacral ganglia this is a chronic infection |
| What salt stabilizes orthomixoviruses and paramixoviruses? | MgSO4 |
| What salt stabilizes herpesviruses? | Na2SO4 |
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