Bacterial viruses Flashcards
what are bacteriophague
Viruses that infect bacteria
morphology of bacteriophague
Binal symmetry – having both
Icosahedral and helical symmetry. It has a head/capsid made of DNA, a sheath (tail), tail fibers and a base plate
what are the types of bacteriophague
Virulent- Lytic multiplication cycle
Temperate- Lysogenic multiplication cycle
what are the main stages of the Lytic cycle
adsorption, penetration, duplication of phague components: replication of virus genetic material, assembly of new virons, maturation, lysis of weakened cell and adsorption again
what is the eclipse period
The period when complete virions cannot be detected in the cell
Is known as the eclipse period
what are the phases in the one-step growth curve
- Eclipse period
- Latent period
- Rise or Burst period
what is burst size
number of viruses produced
what occurs in the T2 phase
in the T2 phage (infecting E. coli)
Eclipse is = 0-11 minutes
Latent = 12-22 minutes
Rise completed within 30 minutes
Burst size = 100
what is the Phage Life Cycle
Vast majority of phages
* Two life styles
– Lytic (T4) – lyses host cell
– Lysogenic (Lambda) - Instead of
destroying host to produce virus progeny,
the viral genome remains within the host
cell and replicates with the bacterial
chromosome.
what occurs in Lytic Life Cycle - 1
Adsorption to the host cell and
penetration
* ~10 phages for every type of
bacteria
– Viruses attach to specific receptor
sites
* Proteins
* Lipopolysaccharides
* Teichoic acids and cell wall
components
* Carbohydrates
* Sex pilus
– Phages then inject DNA into the cell
* Tail contraction (T4)
* Injection (PRD1)
* Unknown mechanisms
what occurs in Lytic Life Cycle - 2
Synthesis of phage nucleic acids and proteins
– mRNA molecules transcribed early in the infection are
synthesized using host RNA polymerase (1 min)
* Make viral enzymes required to take over the host cell
– Degradation of host DNA (3 min)
– Transcription of viral genes (5-9 min)
* Phage DNA is replicated (5 min)
– Phage DNA sometimes modified protect the phage DNA from host
enzymes that would degrade the viral DNA
* The assembly of phage particles
– Phage mRNA directs the synthesis of capsid proteins and other
proteins involved in assembly and release of the virus (12 min)
– DNA packaged into the head (13 min)
– Phage pieces assembled (15 min)
what occurs in Lytic Life Cycle - 3
Release of phage particles (22 min – 300 new phage particles)
– Many phages lyse their host by damaging the cell membrane and
cell wall
* Holin and lysin + lysozymes
what is holin
enzyme which destabilizes the host cell membrane
(pokes holes)
what are lysin + lysozymes
phage enzyme which breaks host cell
wall (lyses host bacteria)
what are Viroids
Viroids are the smallest
infectious pathogens known.
They are composed solely of
a short strand of circular,
single-stranded RNA that has
no protein coating. All known
viroids are inhabitants of
higher plants, and most cause
plant diseases (has
agricultural significance)
what are prions
Prions are misfolded proteins with the ability to transmit
their misfolded shape onto normal variants of the same
protein. They characterize several fatal and
transmissible neurodegenerative diseases in humans
and many other animals.
who discovered prions
Discovered by Stanly Prusiner in 1982
1997 Nobel Prize in Medicine
what do prions attack
Infectious proteins that attack animals
what do prions cause
Causes transmissible spongiform encephalopathies (TSE).
what are the neurodegenerative diseases in cows
Mad cow disease
what are the neurodegenerative diseases in sheep
scrapie
what are the neurodegenerative diseases in deer and elk
Chronic wasting disease
what are the neurodegerative diseases in humans
Kuru, Creutzfeldt-Jakob disease (CJD) and Gerstmann-Sträussler
what does VIRULENT VIRUS contain
cell lyses
what does TEMPERATE VIRUS contain
no cell lyses
what is lysogeny
WHEN A VIRUS INTEGRATE WITH THE CELL’S
GENOME.
what are lysogenised cells immune from
immune from super infection
In a lysogenic or lysogenised cell the virus is in a state clled…
a state called prophague
What is the lysogenic state
there is viral DNA and a bacterial DNA molecule. They are joined together, but their shape isnt completley matching and then they join completley (full circle) with a spliced viral genome (prophage) and then the DNA splits and the bacterial and viral DNA are seperate
what is lysogenic conversion
It is when a temperate phage induces a change in the phenotype of
the infected bacteria e.g.spread of virulence factors, such as
exotoxins and exoenzymes, amongst bacteria
explain the Propagation of Bacteriophage
infect bacteria and mix with molten soft agar, then put it on a plate and observe the plaques
how do we Measuring Phage Number
use plaque assays
What is a plaque assay
method for enumerating the
number of phage particles in a sample; results
are giving in plaque forming units (PFU). You mix phage and bacteria and add it to a 1.5% agar plate
what are plaques
clear zones formed in a lawn of cells due to lysis by phage
how are plaques formed
At a low multiplicity of
infection (MOI) a cell is
infected with a single phage
and lysed, releasing progeny
phage which can diffuse to
neighboring cells and infect
them, lysing these cells then
infecting the neighboring
cells and lysing them, etc,It ultimately results in a circular area of cell lysis in a turbid lawn of cells
Lysogenic cells are immune to…
reinfection by the same
phage (Not immune to infection by other phage types)
what does Corynebacterium
diphtheriae cause
Diphtheria (disease) and Diphtheria toxin (phage encoded property)
what does Clostridium
botulinum cause
Botulism (disease) and Botulinum toxin (phage encoded property)
what does Streptococcus
pyogenes cause
Scarlet fever (disease) and Erythrogenic toxin (phage encoded property)
