L34: Viruses Flashcards
Virus
An infectious particle incapable of replication outside of the host cell. They consist of RNA or DNA genomes (can have either linear or circular genome) surrounded by a protein coat (capsid) and, for some viruses, a membraneous envelope
Describe the discovery of viruses
Tobacco mosaic disease stunts growth of tobacco plants and gives their leaves a mosaic coloration.
The cause of this disease was found not to be a bacteria since the infectious agent was NOT able to grow on nutrient media, a feature not possible for bacteria.
infectious agent was isolated by crystallisation found to be an infectious particle, i.e. virus
capsid
the protein (copied of capsomeres) shell that encloses the viral genome
Viral envelope
A membrane derived from membranes of the host cell, that cloaks the capsid, which in turn encloses the viral genome
Describe the viral replicative cycle
- Viral genome enters host cell
- Viral genome begins t manufacture viral proteins making use of the host cell’s enzymes, tRNAs, amino acids and ATP
- Viral nucleic acid molecules and capsomeres spontaneously assemble new viruses
bacteriophages
A virus that infect bacteria
Name a virus that has two alternative reproductive mechanisms
bacteriophages
- lytic cycle
- lysogenic cycle
lytic cycle
A type of phage replicative cycle resulting in the release of a new phages by lysis (and death) of the host cell
describe: lytic cycle
■ The lytic cycle is a phage replicative cycle that culminates in the death of the host cell
■ The lytic cycle produces new phages and lysis (breaks open) the host‘s cell wall, releasing the progeny viruses
■ A phage that reproduces only by the lytic cycle is called a virulent phage
Describe: lysogenic cycle
■ Every time the host divides, it copies the phage DNA and passes the copies to daughter cells.
temperate phages
Phages that use both the lytic and lysogenic cycles. Switch from lysogenic cycle to lytic cycle is triggered by an environmental trigger causing the virus genome to exit the bacterial chromosome.
How do viruses cause disease
- damaging or killing cells
- triggering adverse immune reactions
vaccines
A harmless derivatives of pathogenic microbes that stimulate the immune system to mount defenses against the harmful pathogen; vaccines can prevent certain viral illnesses
vaccines
A harmless derivatives of pathogenic microbes that stimulate the immune system to mount defenses against the harmful pathogen; vaccines can prevent certain viral illnesses
Prions
An infectious agent that is a misfolded version of a normal cellular protein. Prions appear to increase in number by converting correctly folded versions of proteins into more prions.
