Main content
Course: Class 12 Biology (India) > Unit 10
Lesson 2: Restriction digests, cloning and transformation- DNA cloning and recombinant DNA
- A brief history of restriction enzymes
- Restriction enzyme mechanism
- Parts of a cloning vector
- Features of cloning vectors
- Multiple cloning sites & restriction enzymes
- Insertional inactivation (two antibiotic selectable markers)
- Insertional inactivation using Lac Z gene (Blue white screening)
- Competent cells, transformation, and other methods of DNA delivery
- Cloning sites and insertional inactivation
© 2024 Khan AcademyTerms of usePrivacy PolicyCookie Notice
A brief history of restriction enzymes
Where they come from, why they have such strange names, and more.
This article reviews the history and nomenclature of restriction enzymes - where they come from and why they have such funny names.
Key terms
| Term | Meaning |
|---|---|
| restriction enzyme | enzyme that cuts DNA at specific sites |
| restriction site | sequence that restriction enzyme recognizes and cuts |
| endonuclease | enzyme that cuts nucleotides within a sequence, rather than from the ends |
What are restriction enzymes?
In the early 1950s, scientists noticed that some bacteria were more likely to get infected by viruses than others. Over the next few decades, research revealed that these resistant bacteria had a self-defense mechanism - enzymes that cut DNA into pieces, and so restricted the virus.
These restriction enzymes, or restriction endonucleases, work by recognizing and cutting specific palindromic sequences within the DNA.
What's in a name?
The first such enzyme to be successfully isolated from bacteria was HindII. Since then, thousands of others have been discovered and studied.
You might have noticed that restriction enzymes seem to have pretty strange names. Why are they such complicated sequences of letters and numbers?
The system for naming these molecules is actually quite informative! Each enzyme is named after the bacterium from which it was isolated.
For example, EcoRI comes from:
| Abbreviation | Meaning | Description |
|---|---|---|
| E | Escheria | bacterial genus |
| co | coli | bacterial species |
| R | RY13 | bacterial strain |
| I | first | order in which it was found in this bacterium |
So, EcoRI was the first enzyme to be isolated from the RY13 strain of E. coli. Similarly, HindII was isolated from the d-strain of Haemophilus influenzae.
You are in charge of naming enzymes. Let's try a few.
Let's make up our own restriction enzymes.