Bacteriophage lambda Flashcards
What is the difference between bacteriophage and bacteriophages?
Bacteriophage = singular/plural of same species Bacteriophages = two or more different species
What is an alternative term for ‘bacteriophage’?
phage
What are the main functions of a bacteriophage?
- protection of nucleic acid
- delivery of nucleic acid
- conversion of infected cell to produce phage
- release of phage
Why does a bacteriophage have such a small genome?
It has minimal functions
What is the relationship between a bacteriophage and host?
A bacteriophage subverts the host function in order to replicate.
A bacteriophage cannot survive external to the host.
How are phages classified?
by structure
What is the requirement of the phage structure?
The nucleic acid must be packaged within a protein coat.
What are the three main phage structures?
- icosahedral tailless
- icosahedral with tail
- filamentous
What is an icosahedron?
a quasispherical polyhedron, having twenty triangular faces
Describe an icosahedral tailless phage
The highly compact nucleic acid is located within the capsid, which is in the shape of an icosahedron.
Describe an icosahedral phage with tail
The icosahedral head containing the compact DNA has a tail attached to it.
Describe a filamentous phage
The nucleic acid, which has an extended helical form, is embedded in a cylindrically shaped capsid
What structure is bacteriophage T4 an example of?
icosahedral phage with tail
Why is the icosahedral phage evolutionarily limited?
due to the fixed structural requirements of the head (and tail, if there is one)
define ‘virulent’
always goes through lytic life cycle
define ‘temperate’
- goes through either the lytic or lysogenic cycles
- most bacteria are temperate
define ‘lysogen’
bacterial genome contains a latent form of the phage genome (prophage)
define ‘prophage’
incorporated into the bacterial genome
define ‘immunity’
no further infection possible
define ‘induction’
phage genome is excised from the bacterial genome and the lytic cycle begins
When is lysogeny favoured over lysis?
- low nutrient availability
- high MOI
What does MOI stand for and what is it?
- multiplicity of infection
- the average number of virus particles infecting each cell
Why is lysogeny favoured under low levels of nutrients?
- bacterium is in dormant state
- mRNA degraded and bacterium metabolises at a low level
- therefore lysogeny occurs, since there is no way for the bacterium to induce the lytic cycle
What is a plaque?
clear zones formed in a lawn of cells due to lysis by phage