Test 2 - Viruses + Bacteria Flashcards
What are the major ways that viruses vary (at least 4 main categories)?
- viral size: many different sizes
- naked vs. enveloped (enveloped has membrane bilayer around the outside)
- symmetry: icosahedral vs. helical (icosahedral: capsid protein, nucleic acid inside; helical: often have nucleic acid with capsid proteins around it)
- genome: DNA (ex: dsDNA) or RNA (ex: ssRNA
What are the differences between viruses, virions, viroids, and virophages?
Virus: genetic element that must infect a living (host) cell to replicate
Virion: exists outside host and facilitates transmission from one host cell to another
Viroid: infectious RNA molecules that lacks protein component
Virophage: viruses that infect????
Why are viruses not alive?
- no ‘cell’ structure
- requires host machinery
- no metabolism
- no cell division
Note: they are a life form, though (carry genetic material, reproduce, and evolve)
Why would cells with a DNA genome out-compete those with an RNA genome and lead to the end of the ‘RNA world’? How would viruses have contributed to this process?
Benefits of a DNA genome:
- DNA is more stable (less mutation, more stability)
- better heritability
- stability physically (DNA’s structure) - RNA has extra OH group which is unstable, enzymes at this time could physically degrade RNA
- infection of an RNA cell by a DNA virus –> virus with DNA genome….. It is thought that some RNA viruses evolved DNA genomes. These viruses evolved their own DNA replication machinery to replicate their genomes.
What type of analysis facilitated the generation of a ‘Tree of Life’ that included viruses?
- cannot compare rRNA sequences because viruses don’t have ribosomes
Used proteomics: protein sequences and structural features - compared similarities and differences among folds in different proteins (because protein folding is conserved between eukaryotic, prokaryotic, archaea, and viruses)
What is the basic viral life cycle (5 steps)?
- Attachment
- Penetration - viral RNA enters the cell (envelope fusion, endocytosis, injection)
- Synthesis - protein synthesis
- Assembly - new viral particles assemble
- Release/Mature - Viral particles mature, new viruses released from the cell (budding, lysis, exocytosis)
Where are some points of the cycle that can vary between different viruses?
- penetration/entry of cell: envelope fusion, endocytosis, injection
- release/exit of cell: budding, lysis, exocytosis
What are the 4 possible outcomes of an animal virus infection?
- Transformation: viral proteins promote uncontrolled cell growth (virus changes cell in some way that leads to uncontrolled cell growth)
- lysis: common virulent infection (virus replicates itself and destroys cell)
- persistent infection: involves slow budding (virus still being produced but at a slower rate- less severe, advantageous for virus)
- latent infection: requires genome integration (integration of entire viral genome into host genome)
How can a latent infection change to a lytic infection?
- quality of immune surveillance (ability of immune cell to test virus) is reduced through stress, nutrient limitations, aging, immunocompromized
- It’s a delicate balance. During lytic infection, more viral particles are being produced. During latent infection, viral replication is low (because immune system keeping it low). If balance is thrown off (immune system lightens up), that may lead to the virus replicating more.
What common themes emerged from the YFV activity? Where does your virus fit in? What surprised you about other viruses? What were some characteristics that seemed reasonably unique for certain viruses or families of viruses?
Common themes:
- many animal transmission (some human-to-human) - zoonosis
- many enveloped viruses
- many ssRNA (both - and +) genome type
- some sexually transmitted
My favorite virus: Andes virus (a hantavirus)
- enveloped virus
- single stranded, negative sense RNA virus
- spherical
- zoonotic (infected from rats), person-to-person transmission possible
- causes Andes Virus infection, Andes Hantavirus Pulmonary Syndrome
- prevalent in rural areas, South America
- Andes virus is the only hantavirus that can spread between humans
- There are “New World” hantaviruses (South America - cause Hantavirus Pulmonary Syndrome) and “Old World” hantaviruses (Europe/Asia - hemorrhagic fever with renal syndrome) == same life cycle, basic characteristics but cause different diseases
Surprise/unique:
- many transmitted by bats
- while there is large variety, many overlap
How are antibodies used in the selection process?
- antibody generation is a random process
- different antibodies bind different antigens (same or different protein) -> different effects
(not sure if this answers question)
How does a ‘neutralizing’ antibody work?
blocks the virus
?
How can a ‘non-neutralizing’ antibody enhance viral infection?
bind the virus but do not block important processes
- also enhance uptake
What are some of the reasons that cervical cancer is a particularly high killer in low/middle income countries?
- cost
- lack of information
- difficulty getting the three doses
- lack of access to care
- lack of population level screening for HPV (in many LMICs)
?
What aspect of the bacterial cell dictates the cell morphology? What advantages would variations in cell shape impart?
- Bacteria have a cell wall that dictates the shape.
- ??????
