Viruses and prions Flashcards
What aren’t viruses?
not living; they are acellular
What are viruses?
Small infectious particles
Obligatory intracellular parasites
Inert outside cells and hijack cell replication machinery
What do all viruses carry?
Genome (DNA or RNA)
Capsid (protein coat)
What are DNA and RNA viruses?
Double stranded and single stranded
What can viral protein coats contain?
Viral glycoproteins for cell entry
What are the building blocks of capsids?
Capsomeres
What surrounds some capsids?
Envelope
What is sent to the plasma membrane before a virus buds?
Viral glycoprotein
What happens when a virus has no envelope?
Glycoproteins are attached to the capsid
What is the new plasma membrane of a virus composed of?
Phospholipid bilayer
What is the envelope of a virus a combo of?
Glycoproteins and host cell molecules
What is a wide host range?
Multiple species are susceptible
What is a narrow host range?
Single species/cell in species are affected
What is the host range dictated by?
Lock and key recognition
What does the lock and key recognition mean?
Viral glycoproteins are keys that bind specific host cell surface receptors (locks)
What are the steps of viral replication?
Attachment
Entry
Synthesis
Assembly
Release
What does a virus focus on getting inside of a host cell?
Its viral genome
What is lytic replication?
Bacterial chromosome is destroyed to take away the competition
Same replication cycle
What is cell lysis?
In lytic replication- New phage is released- no envelope
What is the cycle of bacteriophages?
Attachment
Entry
Provirus
Replication of chromosome and virus- (cell division)
Further cell division
Induction
Synthesis
Assembly
Release
What is pro virus?
Step in lysogenic replication cycle in bacteriophage
Means that bacteriophage DNA is integrated into bacteria chromosome
Happens in animal viruses
What are the mechanisms of virus entry?
Direct penetration
Endocytosis
Membrane fusion
What are principles of direct penetration?
Can’t have an envelope
Capsid stays outside cell (what bacteriophage do)
Genome is injected into cell
What is endocytosis?
Membrane of host reaches around and engulfs the virus
Virus is brought into an endosome
The virus is released from the endosome into the host cell cytoplasm
Can be enveloped or non-enveloped viruses
What is membrane fusion?
Can only happen with enveloped viruses
Membrane is brought to the viral envelope and fuses
The viral glycoprotein stays at the surface
What happens in a host cell when invaded by a DNA virus?
Viral genome is replicated by cell DNA polymerase in the nucleus
Host RNA polymerase transcribes DNA to RNA in the nucleus
Ribosome translates RNA into proteins in the cytoplasm
What happens in a host cell when invaded by an RNA virus?
Virus needs special viral enzyme because genome does not match host cell’s
Viral genome is replicated by RNA polymerase in the cytoplasm
Ribosomes translate RNA into proteins in the cytoplasm
New viral genomes and proteins assemble in eukaryotes
Where does DNA viruses assemble in host cells?
Nucleus
Where do RNA viruses assemble in the host cell?
Cytoplasm
How do non enveloped viruses leave host cells?
By lysis (plasma membrane ruptures)
What is another way non-enveloped viruses sometimes leave host cells?
Exocytosis- vesicle with virus inside is transported to cell surface and fusion event allows virus to leave the cell
How do enveloped viruses leave host cells?
Budding
What are prions?
Where are the majority of them?
Misfolded normal cellular proteins
Majority in brain
What can prions cause?
fatal Spongiform encephalopathies
What are the 4 types of spongiform encephalopathies?
Scrapie (sheep), mad cow disease, kuru (New Guinea cannibals), Creutzfeldt-Jakob disease (spontaneous in humans)
How are prions destroyed?
Incineration/autoclaving in concentrated sodium hydroxide
How are prions transmitted?
Ingested
Transplantation
Contact mucous membranes with infected nervous tissue
What is the incubation period for prions?
When does illness occur?
5 to 40 years
12 to 14 months before death
How do prion diseases take over?
Infects brain cell & converts a normal protein into misfolded form
What happens when prions build up?
Neuronal death occurs
Large vacuoles and plaques form; leads to death of the individual
How many types of capsids are there?
4
What do capsids do?
Protect genomes
Where do DNA viruses assemble?
The nucleus
Where do RNA viruses assemble?
Cytoplasm
What is released when a virus is assembled?
Capsomeres and genome
What is the cycle involved in silent replication called?
Lysogenic cycle
What are the 2 methods non-enveloped viruses use to leave a cell?
Exocytosis and lysis
How do non-enveloped viruses enter a cell?
Direct penetration and endocytosis
What are the 2 methods enveloped viruses use to get inside of a cell?
Endocytosis and membrane fusion
What step is unique to lytic replication of bacteriophage?
Bacterial chromosome is destroyed
