Lecture 11: Viruses Flashcards
What is a virus?
A small infectious agent that can only replicate inside the cell of a living organism
What is a phage?
A virus that only infects bacteria
What is a virion?
A virus on the outside of a cell
What are the 3 components of the viral structure?
- Nucleic acid core
- Capsid
- Envelope
Describe the nucleic acid core.
- DNA or RNA
- Single of double stranded
- Circular, linear, segmented, or mixed
What is a capsid?
Protein coat that encases nucleic acids
- May contain lipids
What is the envelope (viral structure)?
Lipid membrane outside the capsid
- Only in some viruses
How are viruses classified?
- By the organisms they infect
- Also shapes: rods and spheres
Why is a small viral genome advantageous?
Faster replication –> an infect other cells faster
One question about the origin of viruses is did they predate cellular life. What evidence supports this idea?
Some viral genomes look different from host counterparts
What are generalists vs. specialists?
What are the types of viral life cycles?
- Lytic: lyses host cell
- Lysogenic: viral DNA merges with host DNA
- Chronic
- Pseugolysogeny: stalled development of the bacteriophage in the host cell, usually caused by unfavorable conditions for the host cell
What are the 2 stages of the viral life cycle?
- Extracellular: inert viral particle in environment
- Intracellular: reproduction stage
What are the general steps of the lytic life cycle?
What are the general steps of the lysogenic life cycle?
DNA is replicated but not translated into proteins
What some defenses bacteria have evolved against viruses (before and after infection)?
- Before infection
- Prevent absorption to surface
- Decoys
- Prevent phage DNA entry - After infection
- Cutting phage nucleic acids
- CRISPR-Cas system
- Abortive infection
The Baltimore classification system classifies viruses based on _____.
nucleic acids
In which class type in the Baltimore classification system would you expect a higher mutation rates?
RNA
- Less mechanisms to correct errors that occur in the replication process
True or false: viruses make up the largest abundance and biomass on Earth
True (15x more abundant than hosts)
Where are viruses mostly found? Where else are they found?
- Mostly in aquatic/marine environments
- Also in soil/desert sand/sea ice
Why are viruses a major driver in the “microbial loop”?
Because they are one of the main causes of mortality among prokaryotes in environment microbial ecosystems
What effects do viruses have on the ecosystem?
What effect did the seastar wasting disease have on its ecosystem?
Decreased ecosystem diversity
- Mussel population grew out of control
- No room for other organisms like barnacle or algae
To which other groups are plant viruses clustering? Why?
Fungi and arthropods
- Probably because they are generalists
