Lecture 20: Day in the life of a Phage Flashcards
what are phage particles outside the cell called?
virions
how do phage find their host?
randomly by moving via diffusion since they have no ATP
how have some phages evolved to improve their hunting efficiency?
decorate their capsids to slow diffusion rate when release
how do phages attach to the cell surface?
tail fibres interacts with specific receptors such as the LPS or a transporter
what do T7 and T4 phages do after landing on the cell?
walk to find their desired protein target
what 3 ways might a host defend against phage attachment?
- downregulated receptor
- structurally altered receptor
- receptor with masked protein
how does T4 phage invade the cell?
has a tail with a spike than drives through the cell wall and cytoplasm
what happens as DNA enters the host cell?
water enters the capsid flushing the rest of the DNA out
why can’t T7 phage invade the host cell the same way as T4?
short stubby tail
how does the T7 phage invade the host cell?
drills into periplasm and builds a tube for DNA to go through
once in the cell what is the first part of the genome encoded for?
a promoter to be recognised by the HOST RNA polymerase
what happens once the host RNA polymerase binds?
starts to read the genome then falls of at the terminator
what protein mimics DNA to avoid restriction endonucleases?
Ocr (overcome classical restriction)
what enzyme inactivates host transcription?
serine kinase
what binds to the HOST RNA polymerase to stop it from recognising promoters?
Gp2
what 2 genes degrade host DNA?
Gp2 and Gp6
what is the point of degrading host DNA?
releases nucleotides for T7 to use to replicate its own genome
what is formed after DNA replication
a concatemer of 100-200 genomes
what is the particle built into before it becomes a virion
procapsid
what enzyme loads the DNA into the capsid?
terminase
what are jumbophages?
phages >250kbp that protect new phages from attack by constructing a nucleus like shell in the host
what do lysins and holins do?
lysins - breakdown cell wall
holins - form channels in cell membrane
