Chapter 9: Viruses and Virology Flashcards
What are viruses?
Obligate intracellular parasites
In what four activities are viruses involved?
- Energy
- Biosynthesis
- Replication of genetic material
- Reproduction
What kind of DNA and RNA do DNA viruses have?
ssDNA and dsDNA
What kind of DNA and RNA do RNA viruses have?
ssRNA and dsRNA
What kind of DNA and RNA do RNA DNA viruses have?
ssRNA (Retroviruses)
dsDNA (Hepadnaviruses)
Name 5 different types of viruses.
- Bacterial viruses
- Archaeal viruses
- Animal viruses
- Plant viruses
- Viruses of eukaryotic cells
What is a virion?
A complete extracellular virus particle, with nucleic acid surrounded by protein coat and other materials
What is a capsid?
Protein coat, surrounds nucleic acid, determines, virus structure
What is a capsomere?
Smallest unit seen with an electron microscope, self assembly
What is a nucleocapsid?
Nucleic acid + protein
What is the envelope?
Lipids layers around nucleocapsid
Describe what a virion looks like?
Using the Tobacco mosaic virus, it is helical and naked
Icosahedrel viruses
- 20 triangular faces
- 12 vertices
Naked vs. enveloped
- Most infect animal cells
- Attachment to host cells
Complex viruses
Influenza and T4
Describe the Influenza virus.
Polymorphic, helical nucleocapsid, buds off cell envelope
Describe the PhiT4 virus.
Icosahdrel head, helical tail
Are enzymes in virions metabolically active or inactive?
Inactive
Name four examples of enzymes in virions.
- Lysozymes
- Polymerases for replication
- Enzymes for transcription of RNA (reverse transcriptase)
- Enzymes for release form host (neuraminidase)
What is a method used to quantify viruses?
Plaque assay
Describe a plaque assay.
- Pour mixture onto solidified nutrient agar plate. This mixture contains molten top agar, bacterial cells, and diluted phage suspension.
- Let solidify.
- Sandwich on top agar and nutrient agar
- Incubate
Animal models
Virus that has no effect on cell culture, but causes death
LD50
Lethal dose for 50% of the population-titer (concentration) of virus that causes half of the animals to die
Describe the viral replication cycle.
- The virion with the DNA inside attaches (adsorption) to the cell (host)
- Penetration (injection) (protein coat remains outside)
- Viral DNA enters
- Synthesis of nucleic acid and protein
- Assembly and packaging
- Release of virions (lysis)
What happens during the eclipse stage of the viral growth curve?
Infectious particles cannot be detected
Describe the attachment of a virus to a host cell.
- External virus protein interacts within host cell “receptor”
- Receptors must be present for infection to occur