Restriction enzymes are functional proteins found in bacteria. Enzymes help speed up chemical reactions, and living organisms use enzymes for a variety of purposes. Specifically, bacteria use restriction enzymes to cut DNA at specific sites. This is useful to the bacteria for protecting against infection, but scientists can also take advantage of the function of a restriction enzyme and there are many different uses for restriction enzymes both by bacteria and in the lab.
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Protecting Against Infection
Bacterial species use restriction enzymes to help protect themselves against foreign DNA. When a virus infects a bacterium, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry," it inserts its genetic material into the bacterial cell. The genetic material then takes over the bacterial cell's gene-replicating machinery, forcing the bacterium to replicate the virus. Eventually, the virus kills the cell and escapes, greatly multiplied in number, to infect more bacterial cells. Restriction enzymes literally "restrict" the ability of the virus to infect a bacterial cell by recognizing and chopping up viral DNA before it can do damage to the cell.
Inserting Foreign Genes
Scientists take advantage of some of the properties of restriction enzymes in the lab. Specific restriction enzymes, called restriction endonucleases, insert segments of DNA into existing segments of DNA, essentially making them a part of an organism's genome. Drs. Mary Campbell and Shawn Farrell, in their book "Biochemistry," explain that by using this property of restriction endonucleases, biochemical researchers can make bacterial species include non-native sequences in their DNA, and produce non-native proteins. Researchers can make Escherichia coli bacteria, for example, produce the human insulin protein by inserting the DNA for the protein into bacterial genomes.
Scientists can also use restriction enzymes to map plasmids, through a process called restriction mapping. A plasmid is a section of bacterial DNA that isn't included in the larger genome, or DNA sequence. Bacteria can pass plasmids back and forth, which spreads genes within a bacterial population. Researchers often want to map plasmids in order to produce specific plasmids, which they then use to insert a specific DNA sequence into a bacterial population, explain Drs. Campbell and Farrell.
Scientists can use restriction enzymes to break a plasmid into chunks, and then test the chunks to determine the DNA sequence of each. From this information, they recreate the full sequence of the plasmid DNA.