Intro To Viruses Flashcards
What is viral replication?
Virus processes new genomes
What are the special cases of viral replication?
Special cases require specific viral enzymes:
- RNA dependent DNA polymerase (reverse transcriptase)
- RNA dependent RNA polymerase (RNA replicase)
What factors define a virus’ tropism?
- the viral glycoproteins (VAP) integrated in the outer coat: either the capsid or the envelope that target receptors are acting as doors on the surface of the host cells(susceptibility)
- Presence of transcription factors allowing expression of viral genes
- Presence of cell enzyme pathways to produce viral proteins is known as “permissivity”
What are viral tropisms?
The ability of a virus to infect a particular host
Might be limited to a single organ, tissue, specialized cell type or range of different organs and tissues
What are the stages in viral synthesis and replication?
- Attachment- to specific host cell receptors: this binding determines what cell can be infected(tropism)
- Penetration
- Uncoating(release of nucleic acid)
- Macro molecular Synthesis
-Early mRNA and protein synthesis:
Proteins to shut off host cell
Proteins to replicate viral genome(if needed) - Postranslational modification of proteins
- Assembly of new virus particles
- Release(lysis of the cell or budding out)
What are the steps in viral penetration and uncoating?
- Injection of the viral genome
- Fusion of the viral envelope with the plasma membrane followed by release of viral genome
- Engulfment of the viral capsid by endocytosis
Differentiate early proteins and late proteins
Early proteins- synthesized early in viral life cycle after uncoating. Also responsible for the replica action of nucleic acid
Late proteins- participate in the formation of viral caspomeres like structural proteins
Briefly state how viral caspids formation
Caspid formation follows a self-assembly mechanism in most of the cases
Some viruses may use chaperones to fold the caspomeres
Briefly state how a viral envelope is formed
During viral release by exocytosis the viral caspids will grab cellular membrane in a form of envelope which is laced with viral proteins
How are virions released from the host cell?
- cell lysis
- Budding from the plasma membrane
Under what circumstances are required for viral multiplication and cultivation ?
Cultivation is only possible in living cells, plants or animals
Describe bacteriophages growing on live bacterial culture
- Bacteriophage+ host bacteria+ melted agar
- Plaque formation is used for phage/virus counting
- PFU(Plaque forming units) counting
- Grown on solid bacterial culture or suspension
What benefits/circumstances permit/encourage viral growth in animals?
- mice, rabbits, guinea pig
- Expensive and ethically controversial
- used in research
What circumstances encourage animal viral growth in embryonated eggs?
- Convenient and inexpensive
- The viral suspension is injected into the fluid of the egg
- Viral growth is detected by death of the embryo or by lesion on the egg membrane
- This is the most common way for production of viral vaccines
What are the types of cell cultures?
Primary cell cultures
Diploid cell strain
Continuous cell line
What is the benefit of cell culture in viral growth compared to animal or egg?
More convenient than animal or egg
How are cell cultures prepared?
Prepared from animal tissues treated with enzyme in order to separate the individual cells
Viral infection leads to cytopathic effect (CPE) and plaque formation
Describe cell behavior in cell culture
- cell culture uses homogenous collection of cells
- The cells are grown as a suspension in solution/medium complimented with nutrients and growth factors
- The cells can also adhere to glass/plastic surface in a form of mono layer
What is a primary cell culture?
- Heterogenous-many cell types
- Closest to animal/tissue/organ
- Technically challenging
Describe the cell culture -Diploid cell strain
- relatively homogenous-fewer cell types
- Further from animal
- Technically less hassle than primary cells
Describe the cell culture-continuous cell line
- Easy to maintain in a suspension or as a mono layer
- Genetically weird-furthest from the primary source
- Immortal
- Most homogenous type
What are possible effects of a virus on a host cell?
- Transformation into a tumor and tumor cell division
- death of cell and release of virus
- Slow release of virus from host cell without cell death
- Causes cell fusion
- Virus present but not replicating(latent infection) which may revert to lytic reaction
Name the 4 physical methods of virus detection and quantification
- Electron microscopy
- Hemmagglutination and hemagglatunation
- Immunoassay
- PCR
Describe electron microscopy as a viral detection and quantification method
A physical method which requires high concentrations and it’s cumbersome and slow
Describe Hemagglutination and hemagglutinatuon as a method of viral detection and quantification
A physical method, fast and easy but is generally not applicable
Describe immunoassay as a viral detection and quantification method
Fast, easy, reliable and widely applicable
Describe PCR as a viral identification and qualification method
Fast, extremely sensitive, and can be quantitative
What is a bacteriophage?
A virus that infects and replicated within bacteria and Archea
List the 5 Biological viral detection and qualification methods
- Plaque assay
- Focus-forming units(FFU)
- TCID50
- LD50
- EID50
What is focus-forming units?
Focus forming units(FFU)
Technique used to quantify viruses that do not lyse the cell to cause any PFU generation.
Relies on fluorescent LH labeled antibodies against viral cell surface cell
What is plaque assay?
A plaque assay is a biological viral detection method that determine the number of plaque forming units in a virus
What is TCID50?
Tissue culture infective dose-50% -biological viral detection method and signifies the concentration at which 50% of the cells are infected
What is LD50?
Lethal dose 50% - a viral biological detection/quantification method detects the amount of a substance/virus that can kill 50% of the test population
What is EID50?
Egg infective Dose 50%
Bacteriophages are ubiquitous…what does this indicate?
Found where ever bacteria exist
Bacteriophages can be either __________ or ________ encoding _______ or ________ genes
Simple.
Complex
Few
Hundreds
What is permissivity?
The presence of cell enzyme pathways to produce viral proteins
What are defective viruses?
Viruses that cannot infect host on its own and need a helper virus
What are satellite viruses?
A type of defective virus that need the complementary function of unrelated helper virus
Give 5 reasons why hepatitis D virus(HDV) is a good example of a defective virus
- very small ssRNA virus
- can only infect with the help of Hepatitis B(HBV)
- shows similarities with the viroids in plants
- produces a protein(delta antigen-HDAg)
Why does hepatitis D require a Hepatitis B?
Hepatitis B virus provides the HBsAg antigen responsible for entry in the host
Where are viroids found?
Only in plants so far
What about virions suggest close evolutional origin?
Various virions are similar to each other suggesting close evolutional origin(~246,375 nucleotides)
How do viroids usually enter?
Through wounds or damaged surface
Describe the genome of viroids
Single stranded close circle RNA
Doesn’t code for proteins but RNA has enzymatic functions
Distribute from cell to cell through plasmodesmata
How were prions first identified?
As transmissible spongiform encephalopathies
What do prions cause?
Loss of motor control, dementia, paralysis, encephalitis, widespread neuronal loss
How can prions be acquired?
- infectious
- hereditary
- spontaneous
How can prions be infectiously caught?
Diet, transfusion, surgical procedures, corneal transplants etc.
Prions can spontaneously be caught?
Rate of about 1 million people usually late in life, or 1-2million infected worldwide
Discuss how can Prions disease be caught due to being hereditary
Prion diseases- autosomal dominant mutation of PrP(chromosome 20)
-at least 10%-15% of total human transmissible SE cases
How do Prions function?
Normal innocuous PrPc can change its shape to a harmful, disease-causing form PrPSc
- thus conversion occurs through a chain reaction(catalytic conversion)
- PrPSc form long filamentous aggregates that gradually damage neuronal tissue
What are viroids?
Infectious RNA particles that don’t have a protein coat
Describe according to the Baltimore system, group 1 viruses with an example
Double stranded DNA(+/-)-herpes
Describe according to the Baltimore system, group 2 viruses, with an example
Group 2- single stranded DNA(+)-sense, parvovirus
Describe according to the Baltimore system, group 3 viruses, with an example
Double stranded RNA (+) sense, rotavirus
Describe using the Baltimore system, group 4 viruses, with an example
Single stranded RNA(+) sense, poliovirus
Describe, according to the Baltimore system group 5 viruses, with an example
Single stranded RNA (-) antisense, measles virus
Describe, according to the Baltimore system, group 6, with an example
Single stranded RNA (+)(RT) with DNA intermediate, HIV
Describe, according to the Baltimore classification, group 7 viruses with an example
Double stranded DNA(+/-) (RT)
Partial dsDNA
Uses reverse transcriptase to enter genome or cell proteins for translation
Hepatitis b
Give an example of Group 1 viruses and how they are encoded
dsDNA is copied for another genome by DNA dependent DNA polymerase(copies both strands)
DNA dependent RNA polymerase makes (+) viral mRNA and translates for viral proteins
Expamples: herpes virus
How are group 2 sDNA Replicated
Sense(+) DNA single strand processed by DNA-dependent DNA polymerase to make dsDNA intermediate
Intermediate processed by dsDNA polymerase to form ss(-)DNA viral genome
How are group 2 viral DNA formed?
Sense(+) DNA single strand processed by DNA-dependent DNA polymerase to make dsDNA intermediate
DNA-Dependent RNA polymerase forms (+)viral mRNA and translated to proteins
How are group 7 viruses translated?
Partial dsDNA becomes full dsDNA and transcribed to mRNA then translated
Which virus group uses reverse transcription?
Group 7, after becoming fully ds(Hepatitis B)
And
Group 6(HIV)
How are group 6 viruses both translated and replicated
Single strand(+) sense converted to ss(-) DNA by RNA-Dependent DNA polymerase
ss(-) is reprocessed by RNA-dependent DNA polymerase and forms dsDNA intermediate
The intermediate can be converted to (+) viral mRNA which be translated OR ss(+) RNA viral genome(original product)
How is group 5 translated and replicated?
(-) antisense strand RNA viral genome either converted to viral protein by RNA-Dependent RNA polymerase or
RNA Dependent RNA polymerase creates ss(+) RNA
then RNA-Dependent RNA Polymerase creates single strandantisense RNA from sense single strand
How are group 3 translated and replicated?
DsRNA -converted to viral mRNA via RNA-Dependent RNA polymerase which is then translated
RNA-Dependent RNA polymerase replicates dsRNA
Which group. Of viruses can be translated to proteins using cell ribosomes?
Group 4- poliovirus(ss+RNA)
How are group 4 translated and replicated?
Translated using ribosomes
Replicated using RNA-Dependent RNA polymerase converts it to ss(-)RNA then viral genome ss(+) RNA
