14:4/ Structure of Viruses 



255 



T phages, in general, do not go through the lysogen stage but enter the 

 vegetative stage directly. In this stage, the bacterial cell starts manu- 

 facturing new proteins and nucleic acids typical of the phage. At the 

 end of a period of development, the nucleic acids are assembled. The 

 proteins are formed into doughnut-like forms about the nucleic acids. 



C,. DNA emptied 

 into solution. 



G. Phage Death. 



F. Just before Lysis. 

 Ca. 100 new phages per 

 bacterium. Additional phage 

 DNA and protein lost into 

 solution. 



E. Formation 

 of new phage 

 particles. 



B,. Attached to 

 broken cell wall. 



A. Inert Phage. 

 No metabolism 



Lysis 



D. Eclipse Period. 

 Vegetative phase during 

 which no phage can be 

 found but host metabolism 

 is dramatically changed. 



Incomplete Phage 



B 2 . Snap Lysis. Too 



many phages per bacterium 



B. Phage attached 

 to host surface. 



C. Phage DNA 

 emptied into host cell. 



Activation 



C 2 . Lysogen Phase. 

 Host metabolism 

 unaltered. 



C?. Reproduction of Lysogen. 

 Phage DNA reproduces and 

 divides at same rate as host cell. 



Figure 5. Life cycle of the bacteriophage. 



These forms are then combined with other proteins to form whole phage 

 particles. Eventually, the bacterium bursts. (This is called "lysis 

 from within," in contrast to "snap lysis" which is lysis from without.) 



The general character of many bacteria may be altered from without 

 by two different processes, each of which bears some resemblance to the 

 phage activity. The first way is by mating or conjugation. In this, 



