Virus Classification - DNA, RNA Flashcards
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Define obligate intracellular parasite
Growth and reproduction of this organism can only occur inside of host cells
A virus is an Obligate intracellular parasite (T/F)
True
What is viral genetic information surrounded by?
Protein in the form of protein capsid
Range of virus sizes
20-300nm
Viruses have a receptor - binding protein for attaching to cells (T/F)
True
Viruses are not host/organ specific (T/F)
False; viruses have host and organ specificity i.e. they can target specific organs in a host or specific hosts
Viruses cannot pass through filters (T/F)
False; viruses are ultramicroscopic unlike bacteria which can be filtered
Which microscope is used to observe viruses
Electron microscope
List 4 main components of a virus structure
Nucleic acid genome, protein capsid, lipid envelope, envelope proteins
Classifications of viruses based on nucleic acids
DNA viruses
RNA viruses
Herpes, Pox, Papovavirus, Parvovirus, Adenovirus, Bacteriophage
- These are DNA or RNA viruses?
DNA viruses
Herpes virus types
Human herpes virus 1 - Herpes Simplex Virus 1
“ “ “ 2 - HSV2
“ “ “ 3 - Varicella zoster virus - chicken pox
Human “ “ 4 - Epstein-Barr virus
Human “ “ 5 - Cytomegalovirus
“ “ “ 6
“ “ “ 7
“ “ “ 8 - Kaposi sarcoma associated herpes virus
Pox virus
Smallpox virus
Are antibiotics used when treating patients with viruses?
No; only if patient is in ICU and has secondary bacterial infection
Icosahedral - define
A polyhedron with 20 faces
Complex viral structure - define
Combination of icosahedral and helical shape and may have a complex outer wall or head-tail morphology e.g. bacteriophage
Enveloped viruses are only double stranded (T/F)
True
Name an icosahedral, ds, enveloped DNA virus
Herpes
Name a complex, ds, enveloped DNA virus
Pox
Naked viruses have no lipid envelope (T/F)
True
The structure of naked viruses consists of both complex and icosahedral (T/F)
False; all are icosahedral
Naked viruses are only single stranded (T/F)
False, both single and double stranded
Name an icosahedral, ss, naked DNA virus
Parvovirus
Name an icosahedral, ds, naked DNA virus
Papovavirus, Adenovirus
+ssRNA vs -ssRNA
a positive-sense RNA virus doesn’t need a polymerase (enzyme) and so the virus is able to make message for the DNA right away without a vital enzyme! It can make viral DNA immediately.
-ssRNA must be converted to +ssRNA before translation to make proteins because -ssRNA is complementary to mRNA.
ssRNA is split into +ve stranded and -ve stranded types of viruses (T/F)
True
Name a +ve stranded, ss, naked RNA virus
Picornavirus, Calicivirus
Name a +ve stranded, ss, enveloped RNA virus
Togavirus, Flavivirus, Coronavirus, Retrovirus
Name a virus that can be either +ve or -ve stranded but single stranded
Arenavirus
Name a -ve stranded, ss, enveloped RNA virus
Bunyavirus, Orthmyxovirus, Paramyxovirus, Rhabdovirus
Name a ds, naked RNA virus
Reovirus
Picorna, Calici, Toga, Flavi, Reovirus all are icosahedral and the rest of RNA viruses are helical (T/F)
True
Structure of naked capsid virus
DNA/RNA + Structural proteins +/- enzymes and nucleic acid binding proteins = nucleocapsid
Structure of enveloped virus
Nucleocapsid + Glycoproteins and membrane
Viruses have two protective layers (T/F)
True - protein and lipid layers
Function of capsid/ protein coat
– Protects nucleic acid from inactivation
– Helps to introduce viral genome into host cell
Capsid is composed of
Capsomers
Capsomer is composed of
Repeating protein subunits blocks that make up the capsid.
Protomers are ?
The polypeptide chains which make up the capsomers
Icosahedral capsid symmetry
12 Corners & 20 Sides
- Two types of Capsomers form the Capsid
- Pentagonal capsomers form the vertices
- Hexagonal capsomers form the sides
Capsid symmetry - helical
Capsomers & nucleic acid are wound together to form a helical or spiral tube
Complex capsid symmetry
The overall shape of virus is quite variable , but mostly they are spherical
Protein subunits seen as projecting spikes on the
surface of envelope are called
Peplomers
A virus may have more than one type of peplomer (T/F)
True
Example of virus with more than one type of peplomer
Influenza virus
Properties of peplomers
- Confers chemical , antigenic & biological properties.
- Susceptible to lipid solvents
Viral replication steps
1) Recognition of host cell ↓ 2) Attachment ↓ 3) Penetration ↓ 4)Uncoating ↓ 5) Transcription ( RNA-dependent RNA transcriptase is carried with virus for -sense b/c needs to be converted to +sense mRNA to form proteins in nucleus) ↓ 6) Protien synthesis ↓ 7) Replication ↓ 8) Assembly ↓ 9) Lysis & release
When is the eclipse phase of viral replication?
From the stage of penetration till the appearance of mature daughter virions
The virions cannot be detected inside the host cell
Duration of eclipse phase
3-12 hours
Viruses can grow on chemically defined media (T/F)
False
Types of Arboviruses
Alpha virus
- Chikungunya
Flaviviridae
–> Mosquito transmission
Hemorrhagic group
- Yellow fever, Dengue
Rhabdovirus
- Rabies virus
In vivo vs in vitro
In vivo - lab bred animals, embryonic bird tissue
In vitro - cell/tissue culture
Why do we culture viruses?
- Isolate + ID viruses
- Research on viral structure, replication effects on host cell
- Prepare virus for vaccine production
How does animal culture work?
Animals are inoculated with the virus and observed for effects which can include death
Virus is isolated and purified from the tissue of these animals.
Match virus to animal inoculation (rabbit, monkey, white mouse, baby white mouse) HSV Rabies virus Dengue virus Polio virus
HSV - rabbit
Rabies virus - white mouse
Dengue virus - baby white mouse
Polio virus - monkey
Animal inoculation isn’t done much anymore - difficulty in choosing animals + care
Which viruses is CAM (chorioallantoic membrane) used for?
Herpes simplexx virus, Pox virus
Which viruses is Amniotic cavity used for?
Inoculation is mainly done for primary isolation of influenza virus and the mumps virus.
What is Amniotic cavity used for?
10 day old embryo
Inoculation is mainly done for production of vaccine of influenza virus, yellow fever, rabies.
Which viruses is the yolk sac used for?
3-8 day old embryo
e.g.: Chlamydiae & Ricketssia
Which viruses is the intraembryonal area used for?
Japanese B encephalitis virus
Pros and cons of inoculating embryonated eggs
Pros
They are free from contaminating bacteria and many latent viruses.
Specific and non specific factors of defense are not involved in embryonated eggs
Cost effective and maintenance is much easier.
Cons
Site of inoculation for varies with different virus. That is, each virus have different sites for their growth and replication.
Primary cultures usually have a limited life span. When cells in a primary culture undergo mitosis and a sufficient density of cells is produced, cells come in contact with other cells.
When this cell-to-cell-contact occurs, mitosis is triggered to stop. This is called contact inhibition and it prevents the density of the cells from becoming too high.
To prevent contact inhibition, cells from the primary cell culture must be transferred to another vessel with fresh growth medium (secondary cell culture).
Purpose of cell cultures in cultivating viruses
For isolation , Neutralization , Production of Antigen for
serological assay
Types of cell cultures
Primary culture :- Made by dispersing cells from freshly
removed host tissues , unable to grow for more than a few passage/sub cultures.
eg : - Rhesus monkey kidney cell & Human
amnion cell culture .
Secondary / Diploid culture :- Diploid cell lines up to 50
passage/ sub cultures but retain their normal chromosome pattern.
eg Human embryonic lung cell culture.
Continuous cell line / Heteroploid cell culture :- Capable of prolonged , infinite growth , derived from cancerous cells ,
grow faster with haploid chromosomes.
eg HeLa cell from cancer of cervix , Hep-2 ( epithelioma of larynx cell ) .
Pros and cons of cell cultures
Pros
Relative ease, broad spectrum, cheaper and sensitivity
Cons
Need trained technicians 24/7
Most hospital labs don’t isolate and ID viruses
What are Cytopathic effects?
Cytopathic effects (CPEs) are distinct observable cell abnormalities due to viral infection.
Which of the following is NOT a cytopathic effect? transformation cell fusion mononucleated cell inclusion bodies
Mononucleated cell
Cell abnormalities resulting from a viral infection are called _____________.
Cytopathic effects
CPEs can include what events in a viral cell?
CPEs can include:
- adherence of red blood cells to the surface of avirus (hemadsorption)
- inhibition of viral reproduction (interference)
- changes in cell shape from flat to round, shrinkage of the nucleus (transformation)
- vacuoles in the cytoplasm, fusion of cytoplasmic membranes and the formation of multinucleated syncytia,
- inclusion bodies in the nucleus or cytoplasm, and
- complete cell lysis
During viral replication, what can be produced?
Inclusion bodies
Inclusion bodies become larger tan viruses and have an affinity for dyes (T/F)
True
Intra vs inter
Intra - inside
Inter - between
Herpes virus , Poliovirus , Echovirus , Coxsackie virus , Influenza virus , Rubella virus , CMV all have inclusion bodies present where in a viral cell?
Nucleus
Herpes virus , Poliovirus , Echovirus , Coxsackie virus , Influenza virus , Rubella virus , CMV all have inclusion bodies present where in a viral cell?
Nucleus; if the virus is made of RNA then it affects cyotplasm and if DNA then nucleus, this is because inclusion bodies form during viral replication
Herpes virus has inclusion bodies where in a viral cell?
Nucleus
Influenza virus has inclusion bodies where in a viral cell?
Nucleus
Poxvirus , Rabies virus has inclusion bodies where in a viral cell?
Cytoplasm
Adeno virus & Measles virus has inclusion bodies where in a viral cell?
Both ( nucleus&cytoplasm)
Cowdry bodies - define
Eosinophilic nuclear inclusions made up of nucleic acid and proteins
Cowdry bodies - define
Eosinophilic nuclear inclusions in viruses, composed of nucleic acid and protein seen in cells infected with Herpes simplex virus
Nuclear inclusions - Abnormal substances in the nuclei
Most viruses are acidophilic, few basophilic e.g. ______.
Adenovirus
Intra nuclear inclusions consist of what types of inclusions?
Cowdry type A and cowdry type B
Cowdry type A is found in?
Yellow fever - Variable size, granular appearance
Cowdry type B is found in?
Polio) - Circumscribed (confined to one area) , multiple
Match the Intra cytoplasmic inclusions to the viruses (Small pox, adenovirus, rabies, measles)
Guarnieri bodies
Negri bodies
Both
Guarnieri bodies ( Small pox ) Negri bodies ( Rabies ) Both ( Measles , Adenovirus )
Bacteriophage - define
Viruses that infect bacteria
Shape of head and sheath of bacteriophage
Capsid ( head ) is polyhedral ,
Sheath is helical
Bacteriophages can pass through bacterial filters (T/F)
True
Bacteriophages have low host specificity
False; high host specificity
Common habitat of bacteriophages
Intestinal tract of animals
Bacteriophage purpose
Bacterial identification; not viral ID
Phage typing - explain
- Classify strains within species of bacteria, each strain is sensitive to a small number of different phages
- Leaves patterns of growth and lysis that can determine the strain.
Phage typing - purpose
Trace the source of outbreaks of infections.
—The viruses that infect bacteria are called bacteriophages and some of these can only infect a single strain of bacteria.
Act as carrier of genes from one bacterium to another
Utilized to study Host - Parasite Relationships
Hemadsorption is used for?
Hemadsorption process
hemadsorption : adherence of red blood cells to the surface of something (as a virus or cell)
Testing presence of Influenza
Influenza virus - Orthomyxoviridae
- Has diff antigens on surface, one of which is HA (Hemagglutinin). Drop erythrocytes of guinea pig onto viral cell culture of Influenza to see if it will be absorbed by the cell surface antigens.
Direct Immunofluorescence Assay (DIA)
- Antibody tagged fluorescent dye on infected cells and view on fluorescent microscope
ImmunoPeroxidase Staining
- Immunoperoxidase staining the cells coated for viral antigens
immune protein called an antibody will attach itself to certain substances, called antigens, that are on or in the cell.
an antibody is joined to an enzyme, peroxidase, that catalyses a reaction in which the protein is specifically stained brown.