Life sciences · Reference
What is a restriction enzyme?
A restriction enzyme is a protein that cuts DNA at specific recognition sequences, acting as molecular scissors — a discovery that made it possible to cut and recombine DNA in the laboratory.
How restriction enzymes work
A restriction enzyme is a type of enzyme that scans DNA for a specific recognition sequence — typically four to eight bases long, often a palindrome — and cuts both strands when it finds one. Some enzymes leave short single-stranded overhangs (sticky ends) at the cut, while others leave blunt ends. The precision of this cutting, always at the same sequence, is what makes restriction enzymes so useful: a given enzyme will cut a piece of DNA only at its particular recognition sites.
A bacterial defence system
Restriction enzymes occur naturally in bacteria, where they form part of a defence system against invading viruses. The enzyme cuts up — restricts — foreign viral DNA, while the bacterium’s own DNA is chemically marked to protect it from being cut.
Their discovery and characterisation in the early 1970s was recognised with the 1978 Nobel Prize in Physiology or Medicine, awarded to Werner Arber, Daniel Nathans, and Hamilton Smith.
Significance in research
Restriction enzymes are a cornerstone of molecular cloning. By cutting DNA at known sequences, they allow a fragment of interest and a plasmid vector to be cut so their compatible ends can be joined, forming recombinant DNA. They are also used to map DNA and to identify sequence differences between samples. Thousands of restriction enzymes with different recognition sequences are now catalogued and used routinely in the laboratory.
Key facts
At a glance
- Also called: restriction endonuclease
- Function: cuts DNA at a specific recognition sequence
- Recognition site: typically 4–8 bases, often palindromic
- Cut ends: sticky (overhanging) or blunt
- Natural role: bacterial defence against viruses
- Nobel Prize: Physiology or Medicine, 1978
Common questions
FAQ
What does a restriction enzyme do?+
A restriction enzyme cuts DNA at a specific recognition sequence. It acts like molecular scissors, allowing researchers to cut DNA at predictable points so fragments can be removed, analysed, or joined to other DNA.
Why are restriction enzymes important in genetic engineering?+
They make it possible to cut DNA at defined sequences, so a gene of interest and a vector can be cut and then joined together. This is the key step in creating recombinant DNA and cloning genes.
Going deeper
Related on CASRAI
- What is recombinant DNA? →
- What is genetic engineering? →
- What is a plasmid? →
- What is an enzyme? →
- Life sciences & molecular biology →
Sources
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