Viral Cells Flashcards
Define the term ‘virus’.
DNA or RNA that is protected by a protein coat
Give the size range of a virus.
25-300nm
How many proteins can be found within a virus?
5-200
Name the extracellular form of a virus.
Virion
What is the name given to a virus that infects a fungus?
A Mycophage
How is the protein coat (capsid) of the virus made?
From a few proteins called ‘capsomers’ that self-assemble
What determines the shape of the virus?
The capsid
What structures are found in a naked virus?
- A capsid/protein coat
- Nucleic acid (RNA or DNA)
- Enzymes
Give an example of a naked virus.
Adenovirus.
Causes colds, pneumonia, and bronchitis.
What structures are found in an enveloped virus?
- A capsid/protein coat
- Nucleic acid (RNA or DNA)
- Enzymes
- Biomembrane (lipids from the host cell)
- Enveloped proteins
Give four examples of enveloped viruses.
- HIV (Human Immunodeficiency Virus)
- Influenza
- Herpes Simplex Virus 1
- Vaccinia virus
What structures are found in a complex virus?
- A capsid/protein coat
- Nucleic acid (RNA or DNA)
- Enzymes
- Complex protein tail
Give an example of a complex virus.
T4 Phage.
Infects bacteria.
Give the three ways that virus particles can enter host cells.
- Endocytosis
- Membrane fusion
- Injection
Explain how a virus can enter a host cell by endocytosis.
- The virus triggers Clathrin-mediated endocytosis
- Enters the cell as a “Trojan horse”
Explain how a virus can enter a host cell by membrane fusion.
Enveloped virus particles bind to receptors in the plasma membrane of host and forces membrane fusion.
Explain how a virus can enter a host cell by injection.
Bacteriophages inject their genetic information and leave the rest of the virus particle behind.
How many structural proteins make up the bacteriophage T4?
25
What form of nucleic acid can be found in the bacteriophage T4?
How many genes?
- Double-stranded DNA
- Over 134 genes
Give the steps to the ‘lifecycle’ of T4 bacteriophage.
- The virus attaches to surface receptors.
- The tail contracts, lytic enzymes break the cell wall, and the core needle pinches the cell.
- The content of the head (proteins, DNA/RNA etc) is released into the cell.
- Bacterial metabolism is disrupted and the genomic DNA is degraded.
- Viral DNA is transcribed into mRNA.
- Viral DNA is replicated.
- Complex viruses self-assemble.
- Lytic viral proteins disintegrate the cell membrane and release the phages.
How many T4 bacteriophages assemble in an infected cell?
50-100
Explain how viruses can use the intracellular transport machinery.
- Motors can bind directly to the viral capsid
- Motors can bind to a virus-containing vesicle
What is required for virus replication?
- Microtubules
- F-actin
What causes the release of the viral DNA/RNA?
Fusion of the endosome and the viral membrane.
