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.

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 :)

thank you, it is


I understand your confusion. Let me explain it step by step to clarify.

Bacteria have a defense mechanism called restriction-modification system, in which they produce enzymes known as restriction enzymes. These enzymes can recognize specific DNA sequences and cut the DNA at those sites. The purpose of this defense mechanism is to protect the bacteria from foreign DNA, such as that of bacteriophages (viruses that infect bacteria).

Now, bacterial genomes have a characteristic feature - they are methylated. Methylation involves adding a methyl group (CH3) to specific DNA bases. This methylation of bacterial DNA prevents the bacteria's own restriction enzymes from cutting their own DNA. In other words, the restriction enzymes do not affect the bacteria's own genome because it is methylated.

However, some bacteriophages have evolved to survive this defense mechanism. They have their own modification system, which methylates their DNA. By doing so, the bacteriophage's DNA mimics the methylation pattern of the bacterial genome, making it resistant to the bacteria's restriction enzymes. This allows these bacteriophages to successfully infect and replicate within the bacteria.

As bacteriophages with methylated genomes become more prevalent, this creates selective pressure on the bacteria. In response, some bacteria may evolve non-methylated genomes and produce restriction enzymes that can degrade the methylated DNA of the bacteriophages. This is because the bacteria can no longer rely on methylation to protect their own genomes, as it would also make them vulnerable to the bacteriophages with methylated DNA.

So, in summary, the initial protection of bacteria comes from their own restriction enzymes that do not affect their own methylated genome. However, some bacteriophages have developed the ability to evade this defense mechanism by methylating their own DNA. This then selects for bacteria that can degrade the methylated DNA of the bacteriophages. It's an ongoing evolutionary battle between bacteria and bacteriophages to gain an advantage in their interaction.