Restriction enzymes recognize and cleave specific DNA sequences, allowing for genetic manipulation in fields such as medicine and agriculture. These enzymes are isolated from bacteria and protect the organism from foreign DNA. Different types of restriction enzymes create blunt or jagged cuts, which can be joined with DNA ligase. Researchers can selectively cut DNA samples into fragments using known restriction enzymes.
Restriction enzymes are enzymes that recognize particular DNA sequences and cleave them, separating one strand of DNA into two wherever they find the sequences they have been coded to recognize. There are a number of applications for restriction enzymes, perhaps most notably in recombinant DNA technology that allows scientists to manipulate genetic information. Recombinant DNA is used for everything from developing therapeutic products like insulin for medical treatment to modifying crops.
These enzymes are isolated from bacteria. In bacteria, they protect the organism from foreign DNA by cutting the DNA when it is recognized by the body of the bacterium. Bacteria use a technique called restriction modification to protect themselves from their own restriction enzymes, ensuring that the enzymes do not turn on the bacterium’s own DNA. As a self-defense mechanism, restriction enzymes are excellent, preventing the replication of foreign DNA in the body by breaking it down.
Numerous restriction enzymes have been discovered, and more are constantly being discovered in a process known as restriction enzyme mapping. Several labs make restriction enzymes to sell to researchers and other labs. Each restriction enzyme has been coded to respond to a particular sequence of nucleotides, and the sequence is usually a palindrome, reading the same back and forth. When a restriction enzyme finds the sequence it recognizes, it cuts both strands of the double-stranded DNA structure, separating it. It will also create more fragments if it identifies more than one copy of the sequence it knows about.
Some restriction enzymes directly cut the double helix, creating so-called blunt ends. Others cut in different places on other sides, making a jagged cut called a “sticky end.” In both cases, an enzyme known as DNA ligase can be used to join a piece of DNA to the severed DNA, as long as the two pieces have complementary ends. This technique can be used to insert new DNA into a genome and to manipulate a genome, a bit like putting the pieces of two different jigsaw puzzles together.
In some cases, a restriction enzyme is coded for so-called unique recognition, which means that it only recognizes very specific sequences. Others are coded for ambiguous recognition, looking for sequences in which specific nucleotides enclose any nucleotides. Using known restriction enzymes, researchers can selectively cut a DNA sample into fragments known as restriction fragments.
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