Viruses - origin & evolution Flashcards
How long have viruses been estimated to be on Earth before humans evolved?
3.5 billion years
This indicates the ancient presence of viruses in the Earth’s biological history.
What is coevolution in the context of viruses?
The process where viruses evolved alongside other species.
What percentage of the human genome contains segments of viral DNA?
Around 8%
These segments are remnants from ancient infections.
What are endogenous retroviruses (ERVs)?
DNA fragments thought to be left over from ancient infections.
What challenge exists in studying the evolution of viruses?
Viruses are not found in fossils, limiting evidence for their evolution.
What are the three theories for the origin of viruses?
- escape theory
- regressive / reduction theory
- virus-first theory
What is the escape theory regarding the origin of viruses?
Viruses arose from genetic elements that gained the ability to move between cells.
What does the regressive/reduction theory suggest about viruses?
Viruses are remnants of cellular organisms that became parasites, shedding unnecessary structures over time.
What is the virus-first theory?
Viruses predate their current cellular hosts.
What common features do all viruses share?
- Capsid protein outer boundary
- No cytoplasm within this boundary
- Genetic material (either DNA or RNA)
- Parasitic nature
How do viruses replicate?
Viruses cannot replicate or carry out functions without a host cell.
What is a key characteristic of viral evolution?
Viruses can undergo evolution extremely rapidly.
Which two viruses are examples of rapid evolution?
- Influenza viruses
- HIV
What factors contribute to the rapid evolution of influenza and HIV?
- High mutation rates
- Large population sizes
- Short generation times
What is antigenic drift?
The accumulation of small changes to viral genetic material over time.
How does antigenic drift affect the host’s immune system?
Variation in surface proteins occurs slowly, eventually leading to the immune system not recognizing the virus.
What is antigenic shift?
A major change in viral genetic material occurs in a short time period, producing rapid variation.
What happens during antigenic shift?
- Two or more virus types infect the same cell
- Their genetic material combines
- A new virus is created not recognized by the host’s immune system
Why do vaccines for rapidly evolving viruses need to be updated yearly?
To remain effective against the small, gradual changes occurring due to antigenic drift.
Why has a vaccine for HIV not been successful?
HIV undergoes genetic drift at an unusually rapid rate.
What is a challenge in developing vaccines for viruses undergoing antigenic shift?
The changes are rapid and unpredictable.
What is a suggested method to deal with fast-evolving viruses?
Isolation of infected individuals to stop the spread of infection.
