Viruses Flashcards
What are viruses composed of?
Form of genetic material DNA or RNA
Composed of protein coat called capsid Small and fixed size
No cytoplasm
Needs host cell to perform life function
The escape hypothesis
Viruses originated from bits of DNA and RNA that “escaped” from cells. These escaped genes gained the ability to move between cells and evolved into infectious particles.
The regressive theory
Viruses were once small, parasitic cells that infected larger cells. Over time, they lost genes and cellular structures, becoming simpler and dependent on host cells to survive.
Virus first theory
Viruses predate cellular life, existing as self-replicating genetic material. They may have been precursors to cellular organisms, evolving independently before cells existed.
Host cell
Specilized sites where the virus attaches itself too
Rapidly evolving viruses
High mutation rates allow for resistance against anti-bacterium through antigenic shift and antigenic drift (e.g Influenza and HIV)
antigenic drift
Small, incremental changes in viral genetic material over time cause variations in surface proteins. These accumulated changes can prevent the immune system from recognizing the virus (e.g HIV)
antigenic shift
When two or more different viral strains or viruses infect the same cell, they recombine genetic material, causing major, rapid changes in surface proteins. This produces a completely new virus that the immune system doesn’t recognize, potentially leading to pandemic (eg Influenza)
What is a Lytic Cycle?
The lytic cycle is a viral replication process where the virus injects its DNA into a host cell, replicates rapidly, and causes the cell to burst (lyse), releasing new viruses.
Key steps of the lytic cycle
Attachment – Virus binds to the host cell.
Penetration – Viral DNA/RNA enters the host cell.
Replication and Synthesis – Viral DNA hijacks the host’s machinery to make viral components.
Assembly – New viral particles are assembled.
Lysis – Host cell bursts, releasing new viruses.
What is the lysogenic cycle?
The lysogenic cycle is a viral replication process where viral DNA integrates into the host’s DNA, replicating silently with the host cell until it is triggered to enter the lytic cycle.
Key steps of the lysogenic cycle
Attachment – Virus attaches to the host cell.
Injection/Penetration – Viral DNA is injected into the host cell.
Integration – Viral DNA integrates into the host’s genome, becoming a prophage.
Replication – Host cell divides, copying the prophage along with its own DNA, passing it along to it’s daughter cell
Induction (if triggered) – Viral DNA exits the host genome and enters the lytic cycle.
What is a prophage?
A prophage is viral DNA that has been integrated into the host cell’s genome during the lysogenic cycle, remaining dormant until activated.
What triggers the switch from the lysogenic to the lytic cycle?
Environmental factors like stress, UV radiation, or chemicals can trigger induction, causing the virus to enter the lytic cycle and begin active replication
Differences between the lytic and lysogenic cycles
Lytic cycle: Rapid, destructive (host cell dies), immediate virus production.
Lysogenic cycle: Dormant, non-destructive (host cell survives), virus replicates passively until induced.
