Virus Structure and Multiplication Flashcards
What is a pathogen?
Any parasitic organism causing infectious disease.
What is pathogenicity?
Ability of a parasite to cause disease.
What is virulence?
Degree of intensity of pathogenicity.
What is an inactive virus outside of a cell referred to as?
A virion.
What do viruses exist as intracellularly?
Nucleic acids.
How do viruses play a role in the evolution of bacteria?
They transfer genes between bacteria.
What are bacteriophages?
Bacterial viruses.
Are there any viruses that target archaea?
A few.
What 4 traits are used to classify most viruses into families?
- Genetic relatedness.
- Genome structure.
- Morphology.
- Life cycle.
What is the average size of most virions?
~20 nm.
What do all virions contain?
A nucleocapsid.
What are the 3 capsid shapes?
- Helical.
- Icosahedral.
- Complex.
What are the two functions of the capsid?
- To protect the viral genetic material.
- Aid in the transfer between host cells.
What is a capsid?
A large macromolecule structure that serves as the protein coat of the virus.
What are the characteristics of a helical capsid?
- Hollow tube shape.
- Self-assembles.
- Length of capsid is a function of nucleic acid.
What are the characteristics of an icosahedral capsid?
- Equilateral triangles fused into a spherical shape that encloses genetic material.
- 20 equilateral faces.
- 12 vertices.
- Has ring or knob-shaped units made of 5 or 6 protomers.
What are the characteristics of a complex capsid?
Has characteristics of both helical and icosahedral capsids.
ex: Poxviruses.
What kind of symmetry do large bacteriophages have?
Binal symmetry (head is icosahedral, tail is helical).
What is the outer, flexible, membranous layer surrounding many viruses called?
The envelope.
Where does the envelope usually arise from?
The cell plasma or nuclear membrane of the host.
What are envelope proteins also called?
- Spikes.
- Spike proteins.
- Peplomers.
What are the functions of envelope proteins?
- Viral identification.
- Viral attachment to the host cell.
- Some have enzymatic activity.
- Some have a role in nucleic acid replication.
What does the viral genome look like?
2x or 1x stranded DNA or RNA.
*Linear or circular.
What is step 1 of viral multiplication?
Attachment/Adsorption.
How does the virus attach to the host cell?
Through specific receptors on the surface of the cell.
Is each virus specific to a certain cell receptor?
No, some viruses can use more than one receptor, use more than one host, or both.
What is step 2 of viral multiplication?
Entry into the host.
What portion of the virus enters the host?
The entire nucleocapsid or the entire genome.
What are the 3 methods of entry into the host?
- Fusion of viral envelope with host membrane.
- Endocytosis in vesicle.
- Injection of nucleic acid.
What portion of the virus enters the cell when the viral envelope fuses with the host membrane?
The nucleocapsid.
What are the steps of fusion with the host membrane?
- Viral envelope spikes bind to receptors.
- Lipid bilayer of viral envelope fuses with host cell membrane.
- Nucleocapsid is released into cytoplasm.
*Enveloped virus.
What are the steps of endocytosis into a vesicle?
- Viral envelope spikes bind to receptors.
- Receptor-mediated endocytosis forms an endosome.
- Increased acidity in the endosome allows the nucleocapsid to escape and enter the cytosol.
*Enveloped virus.
What are the steps of nucleic acid injection?
- Capsid protein binds to receptors on cell surface.
- Receptor mediated endocytosis forms an endosome.
- Nucleic acid is extruded from the endosome into the cytosol.
*Non-enveloped virus.
What is step 3 of viral multiplication?
Synthesis stage.
What occurs during the synthesis stage?
All viral components are produced.
What dictates step 3 of viral multiplication?
The genome, specifically ds DNA typical flow and RNA viruses.
What are the three ways genes and proteins can be referred to?
Early, middle late.
What is step 4 of viral multiplication?
Assembly.
What occurs during step 4 of viral multiplication?
Putting all the components together to make a complete virion.
What is step 5 of viral multiplication?
Virion release.
What occurs during step 5 of viral multiplication in nonenveloped viruses?
The host cell is lysed.
What occurs during step 5 of viral multiplication in enveloped viruses?
Budding
What are the steps of budding?
- Viral matrix proteins are inserted into the host cell’s plasma membrane and line the cytoplasmic face of the plasma membrane.
- Nucleocapsid is directed to the plasma membrane by host microtubules.
- Plasma membrane protrudes outward and the nucleocapsid is surrounded by the matrix-lined plasma membrane.
- Neck of the protruding membrane is pinched off and a mature virion is released.
What 2 other structures can the viral envelope be built from?
- Golgi apparatus.
- Endoplasmic Reticulum.
What motility structure on the host cell do some viruses use to propel themselves through the host membrane?
Actin tails.
What are the characteristics of a virulent phage?
- Multiples immediately upon entering.
- Lyses bacterial host cell upon completion.
What are the characteristics of a temperate phage?
- Can reproduce like a virulent phage (lytic).
- Can remain with the host cell without destroying it by integrating its genome into the host genome (lysogenic).
What is the integrated genome and the bacterium called when lysogeny is occurring?
A prophage in a lysogenic bacterium.
What causes the lysogenic cycle to become the lytic cycle?
When the lysogenic bacterium is exposed to stress, triggering excision of the prophage from the host chromosome.
What are the 4 main ways a eukaryotic cell can be infected?
- Active infection.
- Latent infection.
- Chronic infection.
- Transformation into a malignant cell.
What occurs during active infection?
The virus infects the cell, multiplies rapidly, and lyses the cell.
What occurs during latent infection?
The virus infects the cell, then hides dormant inside the cell. Eventually, the latent infection becomes an active infection.
What occurs during chronic infection?
The virus infects the cell, slowly multiplies, slowly releases. Makes sure the cell can recover and continue to provide for the virus.
*May last years.
What occurs during transformation into a malignant cell?
The virus infects the cell, causes tumor suppressing genes to be deactivated, causing the cell to become cancerous.
What are cytopathic effects (CPEs)?
- Degenerative changes.
- Abnormalities.
What organisms do viroids target?
Plants.
What do satellites require to replicate?
A co-infector, normally a virus.
What 2 organisms do satellites target?
- Animals.
- Plants.
What are similarities between viruses, satellites, and viroids?
- All have a genome.
- Satellites and viroids can infect plants.
- All acellular.
- All require hosts.
What are differences between viruses, satellites, and viroids?
- Satellites require a co-infector.
- Viroids are composed only of RNA.
- Satellites can infect animals, viroids cannot.
What does prion stand for?
Proteinaceous Infectious Particle.
What do prions cause?
A variety of neurodegenerative diseases in humans and animals.
What are the 3 forms of contracting a prion disease?
- Inherited.
- Random.
- Transmissible.
What is the more common term for prion diseases?
Transmissible Spongiform Encephalopathies (TSEs).
What are some examples of TSEs in animals?
- Scrapie in sheep.
- BSE in cattle.
- CWD in cervids.
- Mink spongiform encephalopathy in mink.
- Exotic ungulate spongiform encephalopathy in nyala and greater kudu.
What are some examples of TSEs in humans?
- Kuru.
- Creutzfeldt-Jakob disease.
What is the common abbreviation for a normal prion protein?
PrP^C.
How do prion proteins multiply?
One misfolded protein contacts another one and causes it to misfold … .
