VIRUS I Flashcards
What is a virus?
-Contains nucleic acid surrounded by a protein coat
-Viral replication takes place inside the host cells
-CAPSID: generally composed of only a few protein subunits (capable of self-assembly)
What are the basic types of viruses?
-DNA virus: ss or ds
-RNA -> DNA: ssRNA (retrovirus) or dsDNA (hepadravirus)
What is the life cycle of a bacteriophage
1) attachment
2)penetration (coat protein left outside)
3) virus enzymes synthesized
5) nucleic acid replication
5) synthesis of protein coat
6) assembly + packaging
7) release (lysis) -> host cell dies
Where do the virus usually attach
viruses attach to structure like pili, flagella, or receptors
How do viruses penetrate through bacteria cell wall
-packaged material that can drill holes in bacteria cell wall (lysozyme-like proteins
-only necleic acid injected
What does replication look like for lytic cycle
make more phage and break host cell and release new phage
What does a typical growth curve for bacteriophage look like
-two phases
-latent period
assembly and release
time varies depending on type of virus
What is the experimental set up of plaque assay
-phage dilution and bacterial cells mix together on top of agar
What are phage plaques
-indicate where cell was killed and phage were released to attach to another cell
-each plaque represent 1 viral particle
-size of plaque depends on the virus and host
-not all viruses will infect cells
-viral titer= # of plaque forming units
What type of bacteriophage is Lambda
ds DNA bacteriophage
What is temperate phage
have the option of settin gup a state of coexistence with host cell (lysogeny)
What is lysogeny
-genes that would harm the hose are prevented from being expressed, while a small set of genes that provide benefit to the hose are expressed
-integrates into the bacterial genome
What is the genetic switch
-competition between CI and Cro determine lifestyle
-rightward transcription: induction of the lytic genes (Cro)
-Leftward transcription (leads to lysogeny)
-CI: lambda repressor inhibits lytic cycle
What is a switch box
-competetion for binding to OR3, OR2, and OR1
-Pr: rightward promoter
-Prm: leftward promoter
What is CI (lambda Repressor) structure
-dimer
-N-term bind to DNA
-high affinity for the operator sites on lambda genome
What is Cro structure
-dimer
-can also bind to all three operator sites on lambda genome
What is negative control look like for lambda
-the repressor @ Or2 prevents transcription of Pr transcription through Pr
-No RNA pol binding= no transcription
What does positive control look like for lambda
-repressor @ Or2 helps RNAP bind + increases transcription of Prm approximately 10X
-binds to RNA pol alpha c+d to promote leftward transcription
What does cooperative binding look like for lambda
-repressor can bind to both sites while interacting w/ each other (more stable)
-binding to Or1: repressor has greatest affinity + stimulates repressor bind to Or2 via protein- protein interactions between dimers
-during lysogeny, repressor is constantly bound to Or2 + Or1 blocking expression of Cro
-Cro preferentially binds to Or3 so it doesn’t block RNAPol binding
-Cro has no cooperative binding
-binding to Or1 + shuts off own transcription (auto regulation)
-high [Cro] = binding to OR1
Explain SOS repair
-damaged DNA binds to recA
-leads to cleavage of lexA repressor
-therefore expression of genes involved with DNA repair
Explain induction by DNA damage
-active RecA cleaves repressor rendering it unable to bind cooperatively
-leads to Cro binding + induction of the lytic genes
-need to run out of the burning house
-DNA damage = cell is under stress
What does CRISPR/CAS systems target
Target DNA or RNA to interfere w/ replication of viruses or plasmid DNA
What is the Cas complex
detect foreign DNA or RNA + saves a bit (CRSIPR locus)
What is the CRISPR locus
repeat-spacer unit
-folds into a hair pin structure at one end of the guide RNA
How does Cas used Guide RNA
uses it to target foreign DNA and cleave it
What is PAM
is a short recognition site that stabilizes CAS during cleavage
-spacers= immune memory
What transcribes guide RNA
CRISPR locus transcribed guide RNA on 2nd exposure
