Viruses Flashcards
List the classification criteria for viruses.
1 - Single stranded or double stranded genome.
2 - RNA or DNA.
3 - Sense or antisense.
Define viroid.
Plant pathogens formed of small, rod-like RNA molecules.
Define prion.
Pathogenic proteins that affect protein folding.
List 3 properties of prions that make them difficult to treat.
What gives prions these properties?
1 - They are resistant to heat inactivation.
2 - They are resistant to radiation damage.
3 - They are resistant to DNAse RNAse treatment.
- Prions have these properties as they contain no nucleic acid.
Why are viruses unable to undergo mitosis independently?
Because they contain no organelles.
List the 7 groups of viruses.
1 - Double stranded DNA viruses.
2 - Single stranded DNA viruses.
3 - Double stranded RNA viruses.
4 - Sense RNA viruses.
5 - Antisense RNA viruses.
6 - RNA reverse transcribing viruses.
7 - DNA reverse transcribing viruses.
Give an example of a double stranded DNA virus.
Herpes virus family.
Give an example of a single stranded DNA virus.
Parvovirus.
Give an example of a double stranded RNA virus.
Rotaviruses.
List 3 examples of sense RNA viruses.
1 - Polio.
2 - HCV.
3 - FMDV.
List 2 examples of antisense RNA viruses.
1 - Influenza
2 - Ebola.
Give an example of an RNA reverse transcribing virus.
HIV.
Give an example of a DNA reverse transcribing virus.
HBV.
Define virion.
The infectious stage of the virus lifecycle.
Define capsid.
The protein coat of a virus that surrounds the nucleic acid.
What is Baltimore classification?
What is the advantage of this classification system?
A system of classifying viruses based on their genome.
The advantage is that the behaviour of viruses of the same group can be predicted.
List the stages of the viral life cycle of a sense RNA virus.
1 - Entry.
2 - Disassembly.
3 - Replication of genomes.
4 - Assembly of genomes.
5 - Release of multiple viruses.
How do RNA retroviruses produce DNA that can be integrated into the host cell?
By making a reverse transcript of their RNA.
List the 3 phases of viral growth.
1 - Eclipse phase.
2 - Log phase.
3 - Plateau.
What does the eclipse phase of viral growth represent?
The virus adsorbing onto cells and beginning to utilise the host cell’s apparatus.
What does the plateau phase of viral growth represent?
The end of replication (further growth will occur, but will not be shown on a one-step growth phase).
How do viruses that replicate by lytic infection differ visually from other viruses?
- Viruses that replicate by lytic infection tend to be naked particles (capsids with spikes).
- Viruses that bud chronically from infected cells tend to pick up a membrane as they leave, so are called ‘enveloped’.
Define tropism.
The property of a virus to infect cells by binding to a specific surface receptor.
Describe the tropism of HIV.
HIV binds to:
1 - CD4 cell surface receptors.
2 - CCR5 cell surface receptors.
List 2 cells that can be infected by the HIV virus.
1 - Macrophages.
2 - CD4+T cells.
What is the name of the pattern of diseases associated with HIV?
Autoimmune deficiency syndrome (AIDS).
How many times does the chemokine receptor cross the cell surface membrane?
7.
How does the CDR5-delta 32 mutation give immunity to HIV?
The mutation results in a smaller CCR-5 receptor that lies intracellularly rather than on the cell surface.
Define zoonosis.
Give an example of a zoonosis.
- An infectious disease caused by bacteria, viruses or parasites that spreads between species.
- E.g. ebola.
What is the cause of antigenic variation in influenza?
Influenza is able to undergo genetic reassortment.
List 2 important proteins of the flu virion surface.
1 - Haemagglutinin.
2 - Neuraminidase.
What is the function of haemagglutinin?
A protein responsible for haemagglutination.
Explain why domestication of animals increases the risk of viral infection.
- Different species carry different strains of viruses.
- Domesticating different species may lead to reassortment between the different strains.
- New strains can be created.
List 2 examples of targets for antiviral medications.
1 - Blocking the cell surface receptors to which viruses bind.
2 - Interfering with intracellular replication of the virus.
Define virally encoded host cell shutoff (VEHCS).
The production of viral proteins which prevent host gene expression by blocking host transcription, suppressing mRNAs or translation.
How does polio induce virally encoded host cell shutoff?
- Normally, translation is initiated when ribosomes bind to the m7G cap of the mRNA via the cap binding complex.
- The poliovirus produces a protein known as protein 2A, which cleaves the cap binding complex.
How is polio able to carry out translation if it expresses protein 2A?
Polio’s genome contains an internal ribosome entry site (IRES), which doesn’t require a cap-binding complex for translation to occur.
What is eIF4G?
A component of the eIF4F cap binding complex which acts as the bridge between the m7G cap of the mRNA and the 40S ribosome unit.
How does HSV evade the immune response?
- When HSV infects a cell, it incorporates its genome into the nucleus of the host cell but does not produce proteins (it is quiescent).
- The virus instead produces mRNA transcripts called latency associated transcripts (LATs).
- The immune recognition requires production of proteins, however the latent HSV doesn’t make any.
What do LATs produce?
What is the function of this product?
Micro RNAs, which act to control the host cell.
What is the advantage of a virus incorporating its genome into the nuclei of gametes?
Which viruses do this?
- The products of their genome will be recognised as self in the second generation.
- These viruses are known as human endogenous retroviruses (HERVs).
List 3 viruses that cause acute infection.
1 - Rhinovirus.
2 - Rotavirus.
3 - Influenza virus.
Give an example of a virus that causes persistent infection.
Lymphocytic choriomeningitis virus.
Give an example of a virus that causes persistent, latent infection.
Herpes simplex virus.
List 3 viruses that cause persistent, slow infection.
1 - Measles virus.
2 - HIV.
3 - Human T-lymphotropic virus.
What causes most of the common symptoms of viral infection?
The general effects of the innate immune response.
Define interferon.
A group of signalling proteins made and released by host cells in response to the presence of viruses.
How does interferon bring about changes in nearby cells?
By stimulating the expression of interferon stimulating genes (ISGs), increasing antiviral defences.
