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)
