Homework Help: ap biology again

Posted by claudia on Friday, January 4, 2008 at 5:50pm.

In order to answer a question I must use this information but I find it very confusing.
The restriction enzymes of bacteria protect the bacteria from succesful attack by bacteriophages, whose genomes can be degraded by the restriction enzymes. The bacterial genomes are not vulnerable to these restriction enzymes because bacterial DNA is methylated. This situation selects for bacteriophages whose genomes are also methylated. As new strains of resistant bacteriophages become more prevalent, this in turn selects for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA.
What I find confusing is that it is first saying that the restriction enzymes do not affect the bacteria because its genome is methylated and that the ensymes protect the bacteria well against the bacteriophage by degrading its genome but then it says that the bacteriophage's genome is also methylated so I feel it is a bit confusing. If you are able to help thank you in advance.

ap biology again - Jake1214, Friday, January 4, 2008 at 8:00pm
Yeah, that's a bit confusing. Here is what I think they're trying to say:

-Because unmethylated bacteriophages will be degraded by the restriction enzymes found in bacteria, natural selection will favor those bacteriophages that have methylated DNA sequences (which enable them to successfully attack the bacteria).

-Because of that, bacteria now need to alter their strategy to protect themselves from bacteriophages' attack. They did this by now having their DNA unmethylated and have their restriction enzymes degrade methylated DNA (which will now degrade the methylated bacteriophage).

-This is an example of an evolution arm race... which will never end. Another example is HIV and antibiotic... it's very similar how HIV develop resistance to a certain antibiotic and the antibiotic will no longer have any effect on the virus. Usually doctors will prescribe another type of antibiotic and altering back and forth between different type of antibiotics because the virus also changes its resistant trait.

Hope that helps :)
ap biology again - claudia, Friday, January 4, 2008 at 11:35pm
thank you, it is
helpful

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