bacteriophage

Question 1

are all phages identical

Answer 1

they are all highly diverse:
- type of nucleic acid
- morphology
-Tailed phages (dsDNA with a tail) are the most abundant
-

Question 2

structure

Answer 2

Genomic material (linear dsDNA for tailed phages)
Protein content (structural proteins)

A capsid encloses and protects the dsDNA
A tail, long contractile, long non-contractile, short
Adsorption apparatus (baseplate, tail fibers, tail spikes, tail tip)

Question 3

how does absorption occur

Answer 3

1. First contact of the phage with a “receptor” on the cell surface
   reversible adsorption (WEAK)
2. Phage “walks” on the cell surface to find an ideal place to adsorb irreversibly
   (STRONG)
3. DNA ejection into the cell
   (may or may not be aided by proteins that degrade the inner membrane)

Question 4

absorption to host

Answer 4

between gram
distinct surface compositions
Usually phages infecting species of Gram+ cannot infect species of Gram-

within gram
species and strains diverge in the surface molecules displayed
Phages can only infect a limited number of strains

Question 5

tail ejection

Answer 5

Look like a screw and screws down into the membrane- peptidoglycan layer degraded release of DNA.
pushes baseplate through membrane to release DNA

Question 6

lytic cycle

Answer 6

1. phage absorption
2. DNA injection
3. hijack host machinery for genome replication and protein expression
4. DNA packaging and viron assembly
5. cell burst and release of phage

Question 7

lysogenic cycle

Answer 7

1. phage absorption
2. DNA injection
3. genome integration
4. prophage DNA replicates with the cell

Question 8

how do they decide between lytic or lysogenic

Answer 8

1. only kill enough bacteria to have high conc inside them
   lytic or lysogenic decision- made by

the environment- like an abundance of bacteria and growth conditions
e.gif it stresses like rain in soil causes stress to bacteria which causes bacteriophage to enter the lytic stage to adapt to environment

molecular-
arbitrium released from phage binds to regulator and allows for aimx to be expressed - enters lytic cycle

when arbitrium is to high, means there are too many virions around bacterial cell, so phage decides to not initate any longer

Question 9

pseduo- lysogeneic cycle

Answer 9

1. phage absorption
2. DNA injection
3. phage DNA neither replicates nor integrates
4. phage DNA carried by ONE of the daughter cells

Question 10

why pseudolysogeny?

Answer 10

• increases mutation and stays hidden
• tail fibres that allow reversible and irreversible binding allow for mutation to increase specificity for other hosts

Question 11

generalised transduction

Answer 11

In generalized tranduction, during phage replication, a part of the bacterial DNA is encapsulated instead of phage DNA. When the phage infects another bacteria, it injects the bacterial DNA, and not the phage DNA, which may be incorporated into the genome of a new bacteria. Virulent phages can also do generalized transduction.

Question 12

specialised transduction

Answer 12

In specialized transduction, during excision of the temperate phage of the host genomes, parts of the bacterial chromosome that are adjacente to the phage genome can be taken with the phage genome. After new infection the phage inserts its DNA into a new bacteria, takin with it part of the previous host.