Basic Props Of Viruses Flashcards
What does viruses infect?
Infect all forms of life:
bacteria>> bacteriophage Plants Fungi Insects Fishes Reptiles Birds Mammals
What is the name of the virus infecting bacteria?
Bacteriophage
What is type of viruses
- Obligate Intracellular Parasites : show living capacity only inside the cell ( host cell ) / must live within the cell
Can infect pro/eukaryotes
- Outside a host cell—> inert, no enzyme or other activity.
- Inside the host cell —> viral NA takes over the cell and directs it to produce new viruses —> replication
Does viruses have nucleic acids?
Yes could be DNA or RNA ( not in the same time )
If it goes inside the host cell it takes up the effective cell machineray of the host cell to produce its own proteins and # —> perform replication —> new virus
What is virion?
Basic virus particle that is capable of infecting the host
Intact and infective virus particle
A fully assembled infectious virus with NA and PROTEIN
• At least two components:
Genome
• DNA or RNA
Capsid
• Protective protein coat
Total —> VIRION
What is the size of viruses?
Viruses are small in size
E.coli 2 um
Human cell 6-8 um ( 3 - 4 times larger than E.coli )
Viruses are smaller 20 nm - 400 nm —> ( 100 - 1000 times smaller than what they infect ) —> seen by electron microscope ( submicroscopic particles : not seen with light microscope ) —> can’t be removed by filtered sterilization ( remove bacterial particles only but not the viral particles )
What is the largest size of a virus and what is its name ?
Smallpox (poxvirus, 400 nm) a large virus is at the limit of resolution of the light microscope
What is Armstrong?
10 to the power of - 10
What is the limit of filter sterilization?
200 nm is the filter action limit
> 200 nm will be removed by sterilization
<200nm cannot be removed by filter sterilization
Most of the viruses are beyond the limit —> if filtered —> mostly will monotonous be removed —> go in the filtrate
What is the genetic material of viruses
- DNA or RNA
- Single-stranded or double-stranded
- Linear or circular
- ( sense strand ) or - ( non-sense strand )
- Single or multiple pieces
- Few genes : 3 - 100’s —> don’t have genes for energy production
- Small genome size examples in diff organisms:
A. Parvovirus : 5 kB
B. Poxvirus : 250 kB
C. E.coli: 5 MB
D. Humans : 3.2 Bb
What are the 3 types of DNA viruses ?
- ssDNA, linear: Parvovirus
- dsDNA, circular: Papovavirus
- dsDNA, linear: Adenovirus, Herpes virus, Poxvirus, Hepadnavirus
What are the 4 types of RNA viruses ?
•1. ssRNA, sense (+) strand: picornavirus, calicivirus,
togavirus, coronavirus
- ssRNA, antisense (_) strand: bunyavirus, orthomyxovirus,
arenavirus, filovirus, rhabdovirus, paramyxovirus - ssRNA 2 copies: Retrovirus
- dsRNA, 10-12 segments: Reovirus
What are the types of viruses depending on structure ?
1. Naked (Non-enveloped): e.g. Hepatitis A virus (HAV), Hepatitis E virus (HEV), Norovirus, Parvovirus, etc. ( genome + capsid but NO envelope )
2. Enveloped: e.g. Human immunodeficiency virus (HIV), Herpes simplex virus (HSV), Hepatitis B virus (HBV), Influenza viruses, etc.
What are the simplest viruses?
Naked viruses —> naked nucleocapsid —> ( to remember —> the VIRION is the virus that can infect host cells and contains NA + capsid )
- Capsid —> protein coat —> protectects the genome against nucleases that can digest RNA and DNA
- NA —> genetic material inside the capsid
What is the capsid formed of?
- Protein in nature
2. Many identical protein subunits —> capsomere
How does capsid determine the viral shape?
- Isometric / icosahedral
- Helical
- Some more complex —> helical and isometric together —> most bacteriophages are complex viruses
How can naked viruses attach?
By attaching proteins —> proteins that help the virus infect the cell —> Spikes
What is nucleocapsid?
NA + CAPSID
What are the enveloped virus characteristics?
A. Genetic material
B. Protein coat
C. Envelope:
- Phospholipid bilayer
- External to nucleocapsid
- Attach through spikes to the host cell
D. Matrix protein between envelope and nucleocapsid —> maintain Virion structure
What are the additional comp in some viruses?
They are Enzymes:
- Present in some viruses
- Coded by the virus NA
- Required for viral life cycle
- Not available in the host
Examples:
Have integrase —> attach viral genome to host genome
RNA dependent RNA polymerase —> make new RNA
RNA dependent DNA polymerase —> ( reverse transcriptase ) —> form DNA from RNA
Why viruses cannot reproduce themselves without
assistance?
- Lack machinery for energy harvesting, protein
synthesis, etc. - Must “borrow” this machinery from host cells
—> Obligate intracellular parasites” —> cannot survive on their own
What does viral reproduction require?
- Infection of the host cell
- Genetic material introduced into the host cell
- Host cell:
A. Reprogrammed
B. Produce many copies of the infecting virus
How does the viruse replicate ( steps )
- Attachment (Adsorption)
- Entry (Penetration)
- Replication —> divides inside
- Assembly & Maturation
- Release —> cell burst and virus relaxed
How does step 1 ( attachment / adsorption ) and step 2 happen ?
ATTACHMENT OR ADSORPTION
Spikes attach to specific receptors on the host cell surface
—>diff viruses req diff receptors
—> so cant infect all types of cells
—> some liver cells and some neurons bcz diff types of cells possess diff receptors
ENTRY OR PENETRATION —> viral genetic material enters the cell
- VIRION affixed to plasma mem ( mem fusion )
- Nucleocapsid released to the cytoplasm
- If there is envelope remain attached to the membrane
Lytic vs lyso genie
Lytic life cycle
DNA —> mRNA —> protein —> lysis
Lysogenic
Injected DNA inserted into host chromosome —> provirus or prophage —> most virus genes not expressed —> phases are not produced —> prophage replicates with host
How to determine the no of infectious particles in a viral suspension ?
- Bring a layer of susceptible host cells growing on the surface of the plate
- Add dilute susp of virus
- Cover with agar
- Incubate
- Each plaque ( clear part ) represents cell lysis
What are the disease mechanism of viruses ?
A. By damaging or killing cells —> CYTOPATHIC
B. Inducing immunopathology
C. By transforming cells —> CANCER
Give examples on damaging or killing the cells
- Poliomyelitis —> polio virus —> cytolytic virus that destroys motor neurons in the spinal cord and causes paralysis
- Immunodeficiency —> HIV —> kills CD4+ T cells
Examples of immunopathology
The patient’s T cells attack and destroy virus-infected cells —> Inflammation and cell death
- Jaundice in people with hepatitis virus bcz Of bilirubin bcz it kills the liver cells and they are not able to remove the bilirubin so it leaks to the blood
- With some non-cytopathic virus infections, such as HCV and HBV, destruction of infected cells by CD8+ T cells is the main cause of damage to the liver —> ex : jaundice
- In response to virus infected cells, CD4+ T cells release proinflammatory cytokines leading to to tissue damage.
- Most often, the CD4 + T cell subsets involved are T helper 1 (TH1) cells, but TH17 cells may contribute to inflammatory responses during HIV, HCV and influenza virus infections.
Examples of viruses transforming cells —> cancer
When a virus infects a cell, it expresses proteins that cause the cell to proliferate and/or block apoptosis.
Cancer is multi-factorial: Oncogenic or tumor viruses are very common, only a small % ( 15% ) of people infected actually get cancer.
What are the cancers viruses are involved in?
- Cancer of the cervix: human papilloma virus (HPV)
- Cancer of the liver: hepatitis B or C virus (HBV or HCV)
- Certain leukaemias (human T-cell leukaemia virus type 1, HTLV-1) & lymphomas (Epstein-Barr virus, EBV),
- Kaposi’s sarcoma (human herpesvirus 8, HHV8)
