Viruses Flashcards
Virus
An infectious particle consisting of nucleic acids encoded in a protein coat
Why do viruses “straddle” the definition of life?
1) They can’t replicate on their own: Require a host cell to replicate
2) Also can’t perform metabolic processes on their own
Viral Genome Possibilities
1) Single-Stranded RNA
2) Double-Stranded DNA
3) Double-Stranded RNA
4) Single-Stranded DNA
Virus genome can be…
Continuous or segmented: can be one molecule or multiple molecules
Viruses with segmented genome…
tend to have higher rates of mutation as during replication, recombination of the genome can occur
Capsid
The protein shell enclosing a viral genome
What makes up the capsid?
Capsomeres
–> made of a large number of small protein subunits (usually just the same one or few repeating over and over again)
Capsomere
The protein subunits that make up the capsid
Most animal viruses also contain a…
Viral envelope (AKA membranous envelope)
Viral Envelope
Derived from a host cell’s membrane –> Cloaks the viral capsid and gives the virus the cell’s membrane proteins
Bacteriophage
Viruses that infect bacterial cells
First virus found
Tobacco Mosaic Virus
Viruses are “Obligate Intracellular Parasites” which means…
They can only replicate in host cells
–> Lack metabolic enzymes and the equipment needed for making proteins (Ex: they lack ribosomes)
Why are viruses called “selfish genes”?
Because they only exist to replicate themselves and continue on no matter what
Host Range
The range of species/cells/hosts a virus is able to infect
What determines a virus’s host range?
The interaction between viral surface proteins and host cell membrane receptors
–> Interact in a “lock and key” or “handshake” model
Variation of host range
Some species can have:
1) Narrow host range = can only infect one species/cell type
2) Broad host range = can infect multiple species/cell types
Generic reproductive process of viruses (simple DNA virus)
1) Virus enters cells
2) Virus gets uncoated: releases capsid proteins and viral DNA
3) Some of the viral DNA goes to be transcribed and the rest goes to be replicated to produce more viral DNA
4) mRNA produced from transcription of viral DNA then gets translated to produce more capsid proteins
5) Capsid proteins + replicated viral DNA spontaneously self-assemble
6) New virus is formed and leaves the cell in some manner