Phages

Asked December 15, 2012, 2:16 PM EST

Do all viruses go through the lytic cycle? Can all viruses be called phages? My AP Biology teacher says it is so, but I read in our textbook "AP Edition Biology Seventh Edition" by Campbell/Reece on page 336 "The most complex capsids are found among viruses that infect bacteria, called bacteriophages, or simply phages." And then, on page 337 under "Reproductive Cycles of Phages", "Phages are the best understood of all viruses, although some of them are also among the most complex. Research on phages led to the discovery that some double-stranded DNA viruses can reproduce by two altenative mechanisms: the lytic cycle and the lysogenic cycle."

2 Responses

To answer your questions, yes all viruses will eventually go through the lytic phase. When they enter the cells genome they can either go lysogenic or lytic. Eventually the lysogenic virus will go lytic, this could be days, weeks, months and in some cases years. Think of the commercial on TV for the shingles vaccine. In it they mention how even if you have had chicken pox you can still get shingles. They say this for two reasons - one is that your body should have immunity to it, though that isnt always the case. The other is that the virus can be dormant (lysogenic) in the body and can become lytic.
Now can all viruses be phages...the short answer is no. Phages are viruses that infect bacteria only. One other thing I might add is that viruses are receptor specific, meaning that if the cell surface lacks the receptor they cannot be infected. Receptors on bacteria (prokaryotes) are much different then those on other cells (eukaryotes). That is why viruses that infect bacteria (phages) do not cause disease in people (virus).

Hope this helps

Thank you