Viruses Part A Flashcards
Exam 2
What are viruses?
Acellular organisms that require a host to replicate.
What is expected to be found in every virus?
Nucleic acid and a capsid
What is a nucleocapsid?
The nucleic acid surrounded by a capsid
Polymerase
Help transcribe DNA when virus is infecting
Protease
Help virus take over the host cell
What are the possible capsid structures?
Icosahedral and Helical
What are the building blocks/subunits of an icosahedral capsid?
Capsomers
Does Influenza virus have an envelope?
Yes, and it has spikes containing 2 different proteins: Hemagglutinin (HA) and Neuraminidase (NA)
What does Hemagglutinin (HA) do?
It causes aggregation/clumping when RBC are present
What does Neuraminidase (NA) do?
It is a protease that helps the virus leave the host cell when replication is finished
What type of nucleocapsid does Influenza Virus have?
Helical nucleocapsid
What are the general stages of Viral Replication?
- Adsorption
- Entry
- Synthesis
- Assembly
- Release
What cycle is a temperate phage connected to?
Lysogenic cycle
What cycle are virulent phages and temperate phages connected to?
Lytic cycle
Steps of the Lysogenic cycle
- The phage DNA integrates into host chromosome, where the virus is not actively replicating
- The prophage DNA is copied when the cell divides. No viral proteins are being made
- Exposure to a stress such as UV light triggers excision from the host chromosome
- The viral DNA reaches a resting state, then commits to the lytic cycle
Steps of the Lytic cycle
- Phage attaches to the host and injects its DNA into the cytoplasm
- The phage DNA directs the synthesis of many new phages
- Cell lysis and releases the new phages (now a virulent phage)
- The new phages can bind to other bacterial cells
Viral steps that cause an acute infection
- Adsorption to the host
- Penetration
- Rapid multiplication
- Cell death and viral release
Viral steps that cause a latent infection
- Adsorption to the host
- Penetration
- Virus is present, but does not harm the host
- Activation (Optional)
- Cell death and viral release (triggering an acute infection)
Viral steps that cause a chronic infection
- Adsorption to the host
- Penetration
- Slow release of virus without cell death
Viral steps that cause transformation into malignant cell (cancer)
- Adsorption to the host
- Penetration
- Activation of host proto-oncogene or insertion of oncogene
What was considered when creating viral taxonomy?
Evolutionary relatedness of:
- Nucleic acid type (DNA or RNA, ss or ds)
- Presence/absence of envelope
- Capsid symmetry (icosahedral or helical)
- Dimensions of the virion & capsid
What is the Baltimore System based on?
- Viral genome (DNA or RNA, ss or ds, + or -)
- Process used to synthesize mRNA
How does a double-stranded (ds) DNA virus genome replicate?
dsDNA –> dsDNA
How does a double-stranded (ds) DNA virus mRNA synthesize?
dsDNA –> mRNA
