A2.3 Viruses HL Flashcards
What features do viruses share?
They are small and range in size between 20nm and 300nm
Fixed sizes so they don’t grow meaning they don’t increase in size
All viruses contain genetic material and can be DNA or RNA (never both) and can be either single or double stranded
No cytoplasm as they rely on metabolism of the host cell, this also means few enzymes as no enzymes are required
What features do viruses diversify in?
Size - range in size between 20nm and 300nm some being outisde this range such as the mimivirus and the pithovirus.
Genetic material is either RNA or DNA
viral genomes vary but have the same mission which is to hijack cellular machinery
Viral capsids can range in shapes like helical and icosahedral and very few are also complex
Viral envelopes are either non enveloped meaning cell lysis is the most common exit mode from the host cell. And enveloped viruses which don’t always cell lysis when exiting.
What are the 7 stages of the lyric cycle of a virus?
- Phage attachment to host cell
- Phage DNA entry into host cell
- Phage DNA replication
- Phage protein synthesis
- Assembly of new phage viruses
- Lysis (phage progeny are released)
- Spread
5 stages of lysogenic cycle
- Phage attachment to host cell
- Phage DNA entry into host cell
- Phage DNA is integrated into host genome
- DNA replication
- Cell division
Read book for origins of virus
Didn’t know how to summarise it
Burst size definition
The expected number of curious produced by one infected cell over its lifetime
Do viruses have a high mutation rate?
Yes, especially in RNA viruses because RNA polymerases lack proofreading capabilities which are present in DNA polymerases
What is the definition for mutation rate?
The average number of mutations per nucleotide in the genome per replication cycle
Antigenic drift
Consists of small mutations which can lead to changes in the viruses surface proteins, leading to antigenically different flu viruses.
