Virus Classification, Structure & Replication Flashcards
(35 cards)
What are the attributes for Virus Classification?
1) Virus particle structure
2) Genome
3) Replication Structure
4) Serology
5) Stability
True or false: Every virus has a nucleocapsid
True
What is a nucleocapsid?
RNA or DNA in a core that is protected by a protein coat (capsid), virus particle structure is defined by nucleocapsid structure
What kinds of nucleocapsid structure are there?
Helical, pleomorphic, icosahedral
What are nucleocapsids composed of?
repeating protein subunits called capsomeres
What are viral envelopes?
virus-modified cellular membranes acquired upon exit from host, exposure to lipid solvents in the lab (alcohol, ether, acetone, Freon etc.) render enveloped viruses noninfectious
True or false: Enveloped viruses may have nucleocapsids with different structures.
True
What is the size range of virus particles?
Smallest = 18 nm, Largest = 300 nm
What kinds of DNA are in the viral genome?
Double stranded & single stranded
What kinds of RNA are in the viral genome?
1) Double stranded
2) single stranded
- Plus sense (+) ssRNA - ready to make protein, can sit down on ribosomes and immediately start making viral proteins
- Minus sense (-) ssRNA
- Ambisense
What structures are found in viral genome?
- Linear
- Circular
- Segmented
- Diploid
What is the central dogma?
Main flow of things is DNA –> RNA –> Protein
What do most DNA viruses need that RNA viruses don’t?
Most DNA viruses need access to nucleus of cell and host replication machinery
What do most RNA viruses need that DNA viruses don’t?
Most RNA viruses need RNA dependent RNA polymerase
What are the steps of viral replication?
1) Attachment
2) Entry
3) Transcription
4) Translation
5) Replication
6) Assembly
7) Release
How does attachment work?
1) Virus receptor binds to cellular receptor - Viruses do not usually mimic cell receptor’s normal ligands (they are a spike like projection on particle surface) They may require a co-receptor
* Genetic engineering can change receptor recognition.
What is a major determinant of virus tropism (host range)?
attachment
True or false: Viruses infect essentially all known life forms
True
What is a major factor in virus eradication?
host range (Small pox = humans only vs. Yellow fever = humans and mosquitoes)
How does entry work?
1) Receptor mediated endocytosis, or,
2) Direct penetration of plasma membrane
*Non-enveloped viruses not well understood - pores, and membrane disruption
How does entry work for enveloped viruses?
1) membrane fusion (influenza), HA protein exposed to pH drop = conformational change = allows membrane attachment and fusion
2) Uncoating - Nuclear replication = genome delivered to nucleus, or Cytoplasmic replication = release of genome in cytoplasm then genome is transported to intracellular site of replication (many RNA viruses replicate in membrane associated complexes)
True or false: dsRNA viruses always release their genomic material from the entering particle
False, they NEVER do
How does transcription work?
Messenger RNA (mRNA) templates for protein synthesis are produced. DNA viruses rely on cellular RNA polymerases.
The genome of (+) ssRNA viruses can serve as mRNA (production of new transcripts can occur later using a (-) ssRNA template)
(-) ssRNA, dsRNA viruses have to bring their own polymerases into the cell
How does translation work?
Production of proteins.
All viruses use cellular ribosomes to produce proteins.
Structural proteins are produced in high quantities.
