Restriction Enzymes: Function and Definition Video

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: How Ligase is Used to Engineer Recombinant DNA

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
 Replay
Your next lesson will play in 10 seconds
  • 0:30 Restriction Enzyme Definition
  • 1:32 Recognition Sequence
  • 2:52 Palindromic Sequence
  • 5:12 Sticky Ends
  • 7:20 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Timeline
Autoplay
Autoplay
Speed Speed

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Greg Chin
Restriction enzymes played a critical role in the advent of genetic engineering. In this lesson, you will learn what role restriction enzymes play in creating recombinant DNA.

Genetic Engineering

Restriction enzymes may have evolved to fight invading viruses.
Rest Enz 1

The goal of genetic engineering is changing the genetic makeup of an organism. To achieve this goal, scientists must have a way of rearranging genes to create new combinations of DNA. Restriction enzymes are one tool that can be used to accomplish this goal.

What Is a Restriction Enzyme?

So, what is a restriction enzyme? A restriction enzyme is an enzyme that cuts DNA after recognizing a specific sequence of DNA. You can think of restriction enzymes as molecular scissors. Scientists can use restriction enzymes to cut a single gene from a larger piece of DNA. Restriction enzymes evolved in bacteria.

Now you may be thinking to yourself, 'That seems like something that's too good to be true.' Well, nature didn't create this enzyme just so humans would have a laboratory tool to manipulate DNA. Bacteria, like us, fight a constant battle against viruses. Scientists believe restriction enzymes evolved to protect bacteria from invading viruses.

By recognizing a sequence in viral DNA and cutting the DNA molecule, restriction enzymes inhibit, or restrict, viral infections of bacteria. Let's see how restriction enzymes accomplish that goal.

Recognition Sequence

The restriction enzyme identifies the recognition sequence and cuts it out.
Rest Enz 2

One of the key traits of a restriction enzyme that makes it so valuable to scientists is the fact that restriction enzymes cut at or near a specific sequence of DNA. The DNA sequence recognized by a restriction enzyme is known as the recognition sequence. Let's look at a specific example to see how this works.

The restriction enzyme EcoRI recognizes the sequence GAATTC. Whenever EcoRI sees this particular six-nucleotide sequence, it's going to make a cut in the DNA. Recall that DNA is always read from the 5' end to the 3' end of the strand. If you look more closely at the recognition site, you should notice that the recognition sequence is the same in both strands. If you read the top strand from the 5' to the 3' end, the strand reads GAATTC. However, if you read the bottom strand from the 5' end to the 3' end, you get the same result: GAATTC.

Palindromic Sequence

When a nucleotide sequence is the same whether it is read forward or backward, it's called a palindromic sequence.

You may be more familiar with palindromes in a composition class, where it is defined as a word or sentence that reads the same in both directions. A classic example of a palindromic sentence is, 'A man, a plan, a canal, Panama.'

Let's briefly consider this example. If you start with the last letter of the sentence and work your way toward the first letter, you end up with the same sentence: A man, a plan, a canal, Panama. Note that like the DNA sequence, reading the sentence forward or backward yields the same result.

A palindromic sequence reads the same forward and backward.
Rest Enz 3

How Does It Work?

Great. So, now we know how a restriction enzyme determines where to cut DNA. But, exactly what is it cutting? Recall that there are two types of bonds in a DNA molecule that it could be breaking: covalent bonds and hydrogen bonds. Hydrogen bonds hold complementary nucleotide bases together. Covalent bonds between the sugar and phosphate groups hold the DNA backbone together.

If we think of the DNA strand as a paper streamer to be cut by scissors, should a restriction enzyme cut the hydrogen bonds or covalent bonds to achieve this goal? 'Cutting' the hydrogen bonds would be the equivalent of cutting the streamer straight down the middle. That will not chop our streamer into shorter pieces. Cutting the streamer in that orientation will simply create two skinnier streamers of the same length.

To unlock this lesson you must be a Study.com Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back
What teachers are saying about Study.com
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account
Support