22 Questions
What is a characteristic of herpesviruses that allows them to remain in host cells for a long time?
Viral latency
Which of the following viruses is an example of a herpesvirus that can cause a disease after initial infection and remain latent, causing a new episode of disease later in life?
Varicella-zoster virus
What is the process by which a virus becomes a part of the host cell's DNA?
Provirus integration
What is the term for the ability of a virus to remain in host cells, usually neurons, for a long time?
Viral latency
Which of the following is an example of an emerging virus that may result from an animal virus acquiring the ability to infect humans?
Influenza virus
What is the term for the process by which a latent virus can cause a new episode of disease later in life?
Viral reactivation
Which of the following is NOT a characteristic of herpesviruses?
Host cell lysis
What is the term for a virus that has crossed the 'host species barrier' and can now infect humans?
Emerging virus
What is the requirement for Corynebacterium diphtheria and Clostridium botulinum to cause disease?
They must be infected by a lysogenic phage
What is the outcome of the induction process in a lysogenic cycle?
The prophage is removed from the bacterial chromosome
What is the primary difference between naked and enveloped viruses in terms of adsorption?
Naked viruses have attachment sites, while enveloped viruses have spikes
What is the fate of the majority of bacteriophages?
They undergo lysogenic cycles
What is the result of the lysogenic cycle in terms of the bacteriophage's genome?
The phage genome is integrated into the host cell's genome
What is the trigger for the transition from lysogenic to lytic cycle?
The lack of a specific nutrient or the presence of toxic chemicals
What is the role of the prophage in the lysogenic cycle?
It integrates into the host cell's genome
What is the consequence of the exotoxin release by bacteria?
Tissue damage
What happens to the host cell when new virions are released from it in the case of herpes and pox viruses?
The host cell undergoes lysis and dies
What is the primary characteristic of latent viral infections?
The virus remains dormant within the host cell for an extended period of time
What is the purpose of culturing animal viruses in cell culture?
To provide a controlled environment for virus growth and study
What is the typical outcome of a herpes simplex virus infection?
The virus remains latent within the host cell for an extended period of time
What is the difference between the lytic cycle and latent viral infection?
The lytic cycle results in the death of the host cell, while latent viral infection results in the virus remaining dormant
What is the primary role of enzymes in culturing animal viruses in cell culture?
To free the cells from surrounding tissue
Study Notes
Viral Infection and Replication
- New virions may or may not kill the host cell, depending on the type of virus, such as herpes and pox viruses, which cause lysis to cells.
Latent Viral Infection
- Herpes simplex virus can cause cold sores and remain latent within nerve cells throughout an individual's life.
- When activated by cold, stress, or fever, the virus replicates, resulting in a lytic cycle and another disease episode.
- Varicella-Zoster virus can remain dormant in nerve cells and, when activated, forms a rash along the nerve, causing shingles.
Culturing Animal Viruses
- Viruses must be grown in living tissue, initially in living animals, later in chick embryos, and currently in cell culture (tissue culture).
- Cell culture involves:
- Taking animal cells freed from surrounding tissue by enzymes, washing, counting, and dispensing into plastic flasks, tubes, or bottles with nutrients.
- Examples of viruses grown in cell culture include herpes simplex virus 1 & 2, varicella-zoster virus, cytomegalovirus, and Epstein-Barr virus.
- Most animals are infected with one or more herpesviruses, which can enter a latent state in host cells, particularly neurons.
Viral Latency
- Viral latency refers to the ability of a virus to remain in host cells, usually neurons, for a long period.
- The latent virus can be reactivated later to cause a new episode of disease.
- Example: Varicella-zoster virus causes chickenpox, then remains latent in neurons, and reactivates later in life to cause shingles.
Emerging Viruses
- Emerging viruses are believed to have crossed the host species barrier, allowing animal viruses to infect humans.
- Examples include influenza virus, which can occur when a host cell is simultaneously infected by two different viruses.
Lysogeny
- Lysogenic cycle lasts as long as the bacterium is growing while the prophage is within it.
- The prophage can become active and start the lytic cycle due to certain stimulants (e.g., lack of nutrients or toxic chemicals) or spontaneously.
- Induction involves the provirus removing itself from the bacterial chromosome, coding for viral proteins, enzymes, and other components, and completing the lytic cycle.
Replication of Animal Viruses
- Adsorption: Naked viruses have attachment sites on their capsids that bind to specific receptors on host cells, while enveloped viruses have spikes that recognize membrane protein receptors on the host cell surface.
This quiz explores the relationship between viruses and host cells, including the budding of new virions and the effects on the host cell, including lysis and latency.
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