Lecture 6: Stages 3, 4, 5 Flashcards
Describe a productive infection.
infection of a cell that results in virus replication.
What is viral titer?
The amount of viral load within each cell. Increases by several orders of magnitude.
What is a persistent infection?What are the two types of persistent infections?
An infection that allows the virus and host to coexist. The two types are true viral latency and chronic infection.
What are key ideas about true viral latency?
The virus is dormant. The viral genome is inactive. A specific transcribed gene typically triggers latency. The host cell functions as normal. This can turn “on and off,” meaning the virus will go through stages of latency, then reactivation leading to viral production, followed by more latency.
What are key ideas about chronic viral infections?
The virus is being replicated. Viral particles are being released by infected cells. There is no “latency gene.” Infected cells may enter a resting state where they will stop dividing enter clinical latency. The SYMPTOMS are latent, not the virus replication.
What is the difference between true viral latency and clinical latency?
Viral latency = Virus is NOT ACTIVE
Clinical latency = SYMPTOMS ARE NOT ACTIVE
What is genome integration? How is it related to persistent viral infections?
Viral genome can integrate into host genome during both types of persistent infections; but viral genome stays silent.
What is genome integration called in bacterial cells?
In bacterial cells, genome integration into host genome is called lysogeny.
What is genome integration called in animal/plant cells? What are the two classifications of viruses that can do genome integration?
If it’s non-oncogenic viruses, it’s just called genome integration. If it’s an oncogenic viruses, it can be called oncogenic transformation.
What is apoptosis?
Programmed cell death. Individual cells will suicide, energy is required for this process. Cells will shrink, collapse, and contents will be contained. This process activates the immune system without releasing the virus.
What is necrosis?
Mass cell death. Groups of cells are killed by some injury, cancer, inflammation, or infection. Cells will swell, rupture, then release its contents. The cell will try to delay necrosis.
What is the biggest difference between spherical and cylindrical virus assembly (step 6)?
In spherical viruses, the empty capsid and genome are generated separately. Then, the genome is packed with a molecular motor, requiring energy. Cylindrical viruses pack their genome and assemble their capsid SIMULTANEOUSLY.
Describe how cylindrical viruses assemble? What do their capsids look like?
Rod-like capsid. Genome is folded in the center, and lockwasher protein subunits bind and extend to the growing spiral surrounding it. Capsid formation is complete when all the RNA is packaged.
Define a protomer
The smallest repeating structural unit of a capsid with a defined stoichiometry. Individual proteins come together to create one protomer.
Define a capsomere/capsomer
What forms when protomers are put together. The intermediate geometric subunit.
Define a penton, octon, and hexon.
A capsomere made of 5 protomers, 8 protomers, and 6 protomers. In a soccer-ball shaped capsid, pentons are knitted together with hexons (detail).
Define a procapsid
What forms when capsomeres are put together. The highest order of geometric subunit.
Define a concatemer
A long string of multiple copies of a genome linked in series. Unavoidable product of rolling circle DNA replication.
How do bacteriophages pack their genomes into pre-formed heads?
Genome concatemer will pack a ‘headful’ of DNA into the partially formed head, the concatemer is cleaved, then the remaining tail and tail fibers are added.
What is the first step in assembly of a large icosahedral virus (ie. bacteriophage)?
Procapsid will be built around an internal scaffolding protein. At its vertex will be a molecular motor. Motor is made of portal proteins and pilot proteins. Pilot protein guides genome through the portal, later forming a plug. Lastly, terminase binds to the vertex of the procapsid, bringing with it the viral genome.
What is the second step in assembly of a large icosahedral virus?
The internal scaffolding proteins will degrade (proteolysis) SIMULTANEOUSLY as the portal protein starts to pump genome in via ATP hydrolysis.
What is the third step in assembly of a large icosahedral virus?
When the head is full, temrinase will cut the genome concatemer and release from the capsid.
What is the fourth step in assembly of a large icosahedral virus?
Tail proteins are added, leading to a mature phage.
Describe the structure of the lockwasher.
It consists of 17 long protomers arranged into a single disk. Two disks form a capsomere, called the washer. Upon the correct conditions, the washer will dislocate and look like two turns of a protein helix.
