Nature of Human Viruses Flashcards
Why were viruses considered ‘filterable agents’?
Dmitri Ivanocski took the liquid that causes tobacco mosaic disease and filtered it to eliminate bacteria and spores. The resulting filtered liquid still caused disease, but the infection agent, viruses, could not be visualized.
Viruses are/are not alive
are NOT
Unlike bacteria, viruses cannot ______
replicate in broth
Viruses do not divide by binary fission. Instead, they….
infect a susceptible cell and take over the cellular machinery to make the cell into a virus-making factory
What do viruses require in order to replicate?
Living cells
What does NOT work on viruses?
antibiotics or antifungals
T/F: Some antiviral agents are available, but most viruses have no effective drugs
True
The virus ________ in the newly infected cell to initiate a new infection
disassembles
What do viruses use to complete their life cycle?
They use the host cell machinery to complete their life cycle. (Some people refer to them as obligate intracellular parasites)
What is the genetic material of viruses?
RNA or DNA
New virus particles are made from….
newly made viral proteins in the host cell
What happens to the newly made particles?
The newly made particles (virions) spread the new virus to new cells
A _______ is an infectious virus particle
Virion
Name the two types of viral capsids
Helical
Icosahedral
The _____ capsid can vary in length depending on the size of the viral RNA
helical
For human viruses, what type of viruses all contain helical capsid structures
All negative-sense RNA viruses
What do all helical capsids containing human viruses have?
A lipid envelope. They are all enveloped viruses!!
Most helical capsids do not have what?
do NOT have a rigid structure; think Ebola (spaghetti-like)
Viruses with ______ capsids can be enveloped or naked as opposed to _____ capsids that are all enveloped
icosahedral; helical
What are icosahedral capsids formed from?
From viral capsid proteins. Inside the capsid is the nucleic acid of the virus.
Why do the structure of icosahedral capsids need to be strong?
The structure needs to be strong enough to, in some cases, withstand stomach acid but still be able to open up once the virus has infected a new cell.
What is needed to from the icosahedron?
In many cases, only the viral capsid protein is needed to form the icosahedron. Once a sufficient amount of capsid protein is present, the icosahedron spontaneously forms. This property of capsid self-assembly is used to make the virus-like particles in the human papillomavirus vaccine.
T/F: Viruses are only ‘naked’ (containing no envelope lipid bilayer)
FALSE - Viruses can either be ‘naked’ containing no envelope lipid bilayer or evenloped.
What are viral envelopes derived from?
Infected cell membranes
The viral envelope glycoproteins are incorporated into the lipid bilayer. What are these proteins required for?
Entry into a cell. They disrupt the lipid bilayer, and the virus cannot enter cells.
What prevents a virus from infecting a cell?
Neutralizing antibodies
Neutralizing antibodies recognize ____________ on the virion
surface proteins
Neutralizing antibodies for naked viruses bind….
the capsid proteins
Neutralizing antibodies for enveloped viruses bind the…..
envelope glycoproteins embedded in the lipid bilayer
++ssRNA
For single-stranded RNA viruses, their genome is the same sense as messenger RNA and is called positive-sense RNA viruses
–ssRNA
Negative-sense RNA viruses, –ssRNA, are NOT like mRNA. They must use their genomic –ssRNA as a template to make mRNA
Which viruses have a segmented genome?
BOAR viruses
Most viruses have one continuous segment of genetic material. However, the BOAR viruses have their genome contained in discrete pieces; they have a segmented genome.
What are the BOAR viruses?
Bunyavirus
Orthomyxovirus
Arenavirus
Reovirus
Linear single-stranded DNA (linear ssDNA) members:
Parvovirus
Linear double-stranded DNA (linear dsDNA) members:
Adenovirus
Herpesvirus
Poxvirus
Closed-circular double-stranded (circular dsDNA) members:
Papillomavirus
Polyomavirus
Circular, most of the circle is double-stranded, but a small part is single-stranded (circular ds/ssDNA) member:
Hepadnavirus
Single-stranded positive polarity (+ssRNA) members:
Hepevirus
Picornavirus
Calicivirus
Togavirus
Coronavirus
Flavivirus
Retrovirus (retroviruses have +ssRNA but incorporate two strands of the same RNA into the virion)
Single-stranded negative polarity (-ssRNA) members:
Filovirus
Paramyxovirus
Rhabdovirus
Segmented, single-stranded with negative polarity (segmented -ssRNA) members:
Arenavirus
Bunyavirus
Orthomyxovirus
Segmented double-stranded (segmented dsRNA) member:
Reovirus
Circular single-stranded negative polarity (circular -ssRNA) member:
Deltavirus (this is the Hepatitis D virus (HDV). It is not replication-competent and needs the help of the Hepatitis B Virus (HBV) to replicate).
Describe Steady State virus-cell interactions
-In this infection, the virus does not kill the cell but does produce virus.
-This is productive. The virus is made and is non-cytocidal; the virus does not kill the cell.
Describe Lytic/cytocidal
1) The virus kills the cell as part of its life cycle; cell death is needed to release the virus
2) This interaction is productive and cytocidal. The virus is produced, and it kills the cell
Describe Cytopathic/cytocidal
1) The virus kills the cell but not as part of its normal replication. It just makes the cell so sick that it cannot live.
2) This infection is productive and cytocidal. It also produces virus and kills the cell.
Describe Latent
1) Here, the virus infects cells and does not produce any virus but can reactivate.
2) This is non-productive (no virus made) and non-cytocidal (the cell is not killed).
3) The ability to become latent is an important feature of herpesviruses.
The infected cell can fuse membranes of neighboring uninfected cells to form a large multinucleated cell
Syncytia Forming
Cell-transforming
If a virus can transform a cell, it makes the virus more likely to cause cancer. Transforming a cell makes them immortal and able to grow on top of each other (no contact inhibition like most cells).
List the viruses that cause cancer
EBV
HPV
Human Herpes Virus-8
HTLV
HBV
HCV
EBV
(Epstein-Barr Virus)-Burkitt lymphoma, Nasopharyngeal carcinoma, oral hairy leukoplakia (in HIV infections)
HPV
(Human Papilloma Virus) – Cervical, Anal, and Oropharynx
Human Herpes Virus-8
Kaposi’s Sarcoma (in HIV infections, immunocompromised)
HTLV
(Human T cell lymphotropic virus) Adult T-cell leukemia and lymphoma
HBV
(Hepatitis B virus)-Hepatocellular carcinoma
HCV
(Hepatitis C Virus)-Hepatocellular carcinoma
***As far as the charts of different viruses, of the viruses discussed, you need to know the type of genetic material,
whether it is naked or enveloped, and capsid shape. You will also need to know the family of the viruses
discussed. For example, for HSV-1, know Herpesvirus, enveloped, icosahedral, and dsDNA. A trick to remember
icosahedral or helical is that all DNA viruses are icosahedral. In addition, of the RNA viruses, only the –ssRNA
viruses are helical, except for coronavirus.
See Study Guide #1!!
Herpesvirus Family
“How Simple to Very Easily Catch 6, 7, or 8 Herpesviruses”
-Herpes Simplex 1 & 2
-Varicella Zoster
-EBV
-CMV
-Human Herpes viruses 6, 7, & 8
List all of the DNA viruses
HHAPPPPy
-HBV
-Herpes
-Adeno
-Parvo
-Papilloma
-Polyoma
-Pox
Picornavirus Family
PERCH (with 2 E’s)
-Polio
-Entero
-Echo
-Rhino
-Coxsackie
-HAV
Flavivirus Family
“A WESTern Dentist Zombie YELLed Help”
-West Nile Virus
-Dengue
-Zika
-Yellow Fever Virus
-Hepatitis C Virus
Paramyxovirus Family
PRM3-PaRaMyxo
-Parainfluenza
-RSV
-Metapneumo
-Measles
-Mumps
