11. bacteriophage

bacteriophage stucture

dsDNA virus

polyhedral head

with an attached tail

three families have

complex contractile tail

short noncontractile tail

long noncontractile tail

lytic infection

production of many phage particles

usually lyses cells

virulent phage

lysogenic infection

phage DNA stably maintained in bacteria

usually by integrating into bacterial genome

temperate phage

lytic infection attachment

phages attched to receptor on surface of bacterial cell

receptors: proteins or carbohydrates

lytic infection entry

usually only DNA enter cells

some phage packaging one or a few protiens that also enter cell 

lytic infection step 3

produce phage proteins and DNA

gene expression carefully times do gene expressed as needed

lytic infection step 3: dna synthesis

inhibit bacterial DNA replication, often degrading bacterial DNA

promote phage DNA replication

lytic infection step 4

phage head and tail assemble seperately

largely self assembly

DNA packaged into heads

lytic infection step 5

phage release

lysozyme

degrades peptidoglycan, causes lysis

holin

create a pore in the inner membrane so lysozyme can get to the peptidoglycan

spanin

disrupts outer membrane

requried for phage release

cos site

complementary  ssDNA overhangs, circularize DNA in cell

restriction modification system

natually encoded in bacterial cel

cleav DNA at specific sequences

protect from foreign DNA

crispr 

system allows bacteria to become immune to infection by phage after intial exposure

transduciton

phage-mediated transfer of bacterial DNA sequences

generalized transduction

the particles carrying bacterial DNA form during a lytic infection

errors in DNA packaging

fragments of bacterial DNA are packages instead of phage DNA

specialized transduction

particles carrying bacterial infection form after lysogenic infection

P1

phage plasmid

p1 lysogen: DNA not integrated

lysogens

growth in center of plaque

immune to superinfection

CII

very early gene

initates lysogen formation

lysogeny favored by

low temp

slow growth

high multiplicity of infection

operator sites

binding site for repressor proteins

mainting a lysogen

C1 protiens binds to operator sites, keeps lytic genes off

excision

reversal of integration

requires int and xis