We will take a look at each of these groups in the following section. They protect the bacterium against foreign DNA from other organisms. Invading DNA is cut into pieces and made inoperable. This process is called restriction . As with any enzyme, these are specific in the job they do.
Bacteria protect their own DNA by a process called methylation .
During this process methyl groups are added to the nucleotides within the recognition sequence. There are several hundred restriction enzymes and about 100 different recognition sequences. The restriction enzymes usually cut the phosphodiester bonds of both strands in a staggered manner. The result being both ends have a single stranded area called the sticky ends . It is within this space that the new piece of DNA is added, attaching to the sticky ends.