Ex 19 Bacteriophage

Lab Exam 3

viruses

obligate intracellular parasites that are dependent on host cell for replication

bacteriophage

viruses that infect bacteria

• commonly known as phage

lytic reproductive cycle

infect and kill host cells by causing cell to burst/lyse after viral replication

attachment

phage attach to specific receptor on host cell

• only host cells that contain specific receptor are susceptible to infection

• cells lacking receptor are immune to infection

penetration

phage inject the nucleic acid genome (DNA or RNA, never both) into host cell

• protein capsid remains outside host cell

replication

phage genome encodes for proteins that take over host cell machinery

• direct it to replicate new phage genomes and the proteins required to make the capsid

• reason phage requires host cell

assembly

new phage genomes are packaged within new capsids

• produces intact and infectious phage

release

host cell is lysed and newly assembled phage are released

lysate

clear, phage-containing liquid

• produced from infection and lysis of bacterial host cells in broth

lawn of cells

many host bacterial cells (10^8) cover entire agar surface after incubation

plaques

small circular areas of bacterial cell clearance on lawn of cells

• caused from single phage infecting one bacterial cell

• phage released from that cell infect adjacent cells, causing lysis etc

PFU

one single phage that infects a single original bacterial cell and then replicates and spreads outward to form the plaque

• each plaque is result of one PFU

plaque assay

observes interaction between one type of phage and a susceptible host

titer

PFU/ml concentration of a lysate