Bacteriophage Flashcards
What is a Bacteriophage?
Virus that infects bacteria
Most Bacteriophages have?
dsDNA
Bacteriophages can have RNA as a ___?
genome
A virulent phage has how many reproductive options?
One
What is the one wat a virulent phage can reproduce?
Lytic Cycle
Lytic Cycle
Phage multiplies immediately upon cell entry. Lysis the bacterial host cell.
Temperate Phages have how many reproductive options?
Two
What are the two cycles that temperate phages utilize?
Lytic and lysogenic
Lysogenic cycle
Phage integrates into host cell’s chromosome.
What is lysogeny?
The relationship between a prophage and lysogenic bacteria
When phage DNA integrates into bacterial host cells chromosome, what is its name?
Prophage
Can a temperate phage change the phenotype of its host?
yes
Temperate phage change to bacterial host cell surface achieves what? (Example provided in notes)
Bacteria become immune to superinfection
Temperate phage change to make bacterial host cell a pathogen? (E.g. in ppt)
Phage may express pathogenic toxin/enzyme; cholera, diptheria
What are two advantage of lysogeny for a virus?
Phage remains viable even if it does not replicate. Multiplicity of of infection ensures survival of host cell.
What is the process called ‘induction’?
when conditions in the cell cause prophage to initiate synthesis of new phage particles
What type of Bacteriophage is bacteriophage T4?
A virulent bacteriophage
Phage life cycle culminates w/host cell bursting, releasing virions. What are the steps?
Absorption to receptor on outer membrane
Tail sheath lysozyme/central tube pierce the cell wall
Viral nucleic acid is injected into host cell through tube
Phage Adsorption: attachment of phage onto host. Steps?
Tail fibers recognize receptor protein on cell surface
Baseplate settles down on surface
Shape change of baseplate tail to (24 to 12 rings)
Phage DNA Entry Steps:
Central tube is pushed through cell wall
Baseplate contain lysozyme
Linear DNA is extruded from the head into host
Bacteriophage T4 Life Cycle: Transcription -> early mRNA. What does this result in?
Production of viral encoded DNA-dependent DNA polymerase
Bacterial T4 Life Cycle: Transcription -> late mRNA.
Translation of capsid and lysis proteins
Temporal transcription regulated by:
Alternative E. Coli polymerase factors induced by virus
Early viral gene product stimulate transcription of some late viral genes
Genes w/related functions are usually separated and clustered together
Early gene transcribed…
Counterclockwise
Late gene transcribed…
Clockwise
The T4 Genome/DNA: A large portion of the genome codes for replication-related products including…
Protein subunits of its replisome
Enzymes needed for DNA synthesis (synthesis of HMC)
What is hydroxymethylcytosine (HMC)?
A modified nucleotide replacing cytosine in T4 DNA
HMC is chemically modified by glucosylation
Protects T4 phage DNA from E. Coli restriction enzymes. Enzymes that cleave DNA at specific sequences.
Restriction is a bacterial defense mechanism used against bacteriophage infection
Why is T4 DNA terminally redundant?
Base sequence repeated at both ends.
Allows for formation of concatamers.
What are concatamers?
Long strands of DNA consisting of several units linked together
Concatamers allow for the cleaving of genome for…
Viral progeny packaging
Complex self-assembly process involves viral proteins and host cell factors for …
Capsid assembly
Assembly/Release of T4 Phage Particles: what is the set of proteins that package DNA?
Packasome moves DNA into phage head
Terminase complex generates double stranded ends. (Cuts concatemer and pushes DNA into head)
Release of T4 Phage Particles: Assembly is followed by release in T4 E. Coli system, ~150 viral particles are released. What two proteins are involved in this process?
T4 lysozyme and Holin
What does the T4 lysozyme do?
Attacks cell wall
What does holin do?
creates holes in plasma membrane
What type of Bacteriophage is a bacteriophage Lambda?
Temperature bacteriophage
