Class 4 Flashcards
(45 cards)
What is a virus?
Obligate intracellular parasite
Not living
Cant make energy, rely on host
Made of Protein and nucleic acid
What kind of DNA do viruses have?
Linear, circular. more than 1 reading frame, SS or DS
What are the steps for the bacteriophage too enter the cell
Absorption/Attachement
Infection/Penetration
What happens in the Absorption phase?
Bacteriophage binds all proteins on outside, (proteins serve other functions than to get infected)
Attachment is specific to cell type
-at this point the virus is infectious but the cell is not infected
What happens in the infection stage?
Inject genome into host cell
Cell has peptidoglycan wall so bacteriophage cant go into cell
-at this point the cell is now infected, and the virus is not infectious
What is the lytic cycle?
Makes a lot of viral copies quickly but cell host dies
host machinery translates and transcribes viral genome
Early genes are hydrolase capasid protein
What is hydrolase?
destroys host cell genome
what is the late gene?
Lysozyme which puts hole sin bacterial cell wall and the osmotic gradient will cause water to flow into the cell causing it to burst
What is the lysogenic cycle?
Incorporates the genome and then it waits
- integrates viral genome with host (prophase/provirus) and then cell Is called a lysogen
- Has a repressor protein preventing transcription and translation and host carries on with normal activities and reproduces via mitosis making more copies
- repressor protein must be removed to enter the lysogenic cycle (stress)
What is transduction?
Some of host DNA taken out int he lytic process of the lysogenic cycle
-this provides genetic diversity for bacteria (doesn’t always happen-doest immediately kill the host cell
What is the productive cycle?
Virus doesn’t need to lyse the cell (only animal cells)
- like the lytic cycle but no lysis
- it gets coated int he cell membrane=envelop
What are the advantages of the productive cycle?
Get a lot more virus immediately
They all exit quickly without killing host
Envelope provides immune protection if surrounded by cell membrane
Allows for infection, the virus taken up whole (endocytosis)
RNA viruses need?
Extra enzymes either encodes for that or in capsid
What does a + RNA virus need?
Acts as mRNA and can be directly translated using host ribosome
- needs RNA dependent (reads) RNA polymerase (makes) for transcription so the virus has to code or carry it in its genome
- enzyme is encoded in the virus RNA dependent RNA polymerase
What happens when + is replicated?
it’s - but then it needs to do it again to make it positive
What does and - virus need?
- RNA genome of virus is complimentary to mRNA
- transcription has to happen first to get to + with RNA dependent RNA polymerase
- virus has to carry the enzyme in basic and also codes for RNA dependent RNA polymerase so the new ones have the enzyme
What its another name for a retro virus?
+ RNA lysogenic virus
- genome is mRNA and will be incorporated into hose DNA genome. So virus genes need to become DS DNA
- +–> ssDNA by RNA dependent DNA polymerase then ssDNA–> DSDNA and inserted into the host genome
- at this point can translate and transcribe with host genome
What are the problems with the virus?
- Permentantly in genome
2. Rapid mutation. when tRNA> ssDNA
What is a prion?
Infectious proteins and misfolded version of normal proteins (small)
-they can self replicate and very stable (they are hard ti kill)
What are normal prions?
Normally folded proteins
What are mutant prions?
When misfiled they are mutagenic
How are prions transferred ?
Eat infected tissue
Inherit mutation
Spontaneous mutation in prion gene
How does a prion turn into a bad one?
Bad ones bring good ones to them and make them change conformation to become bad ones
What is a viroid?
Circle RNA No capsid Coinfection (carried in a capsid of another virus) Dont code proteins Block translation
