Sticky Ends of DNA: Definition & Concept

Instructor: Jennifer Gilley
Different pieces of DNA can be cut and pasted together in order to make recombinant DNA. This lesson will describe how sticky ends of DNA are used to do this and will test your understanding with a quiz.

Deoxyribonucleic Acid (DNA)

DNA is the genetic material in our cells that acts as a blueprint for the tens of thousands of proteins in our body. It's made up of a bunch of nucleotides which serve as the building blocks of DNA. The four nucleotides that make up DNA are adenine (A), cytosine (C), thymine (T) and guanine (G). The sequence of these nucleotides serves as a code. Your cells read the code and make a protein that corresponds to that code. Think of it like the alphabet. The alphabet has 26 letters that can be arranged in multiple different ways to make various different words. DNA is the same way, but it's alphabet only has four letters: A, T, G, C. If you change the sequence of DNA, you will change the protein that is being made.

The structure of DNA is complex and is composed of two strands. Each strand is composed of A's, T's, C's and G's and is complimentary to the other strand. A molecule of DNA is complimentary because each nucleotide is paired with a partner. A's will always partner and bind to T's while G's will always pair with C's. So if one strand of DNA read 'ATGCTAT,' the complimentary strand would be TACGATA. Wherever you see an A, it will be paired with a T. Wherever you see a G, it will be paired with a C.

Complimentary DNA
Complimentarity of DNA

Recombinant DNA

Technology has afforded us the opportunity to mix and match different pieces of DNA with one another. Recombinant DNA is a piece of DNA that is made from two or more sources. One molecule of DNA has been recombined with other pieces of DNA. Just think of it as cutting and pasting different pieces of DNA together. Why would we want to do this? Well, by manipulating DNA we can make new proteins that can assist in scientific research and may even be used to treat various diseases.

How is all of this possible? Well, there are sequences in our DNA that determine where it can be cut. These short sequences of nucleotides are called recognition sites and are found all throughout our DNA. Each recognition site is recognized by a particular enzyme called a restriction enzyme. Restriction enzymes act as a pair of scissors and cut the DNA at these recognition sites. Each restriction enzyme is specific to a particular restriction site.

For example, EcoRI is a restriction enzyme that can only recognize a restriction site sequence of GAATTC. Once EcoRI has recognized its restriction site, it will cut the double stranded DNA in a zig-zag pattern. As a result, some of the DNA is single-stranded and not partnered up with its corresponding nucleotides. These parts of the DNA are called sticky ends. They're 'sticky' because they can easily be glued or pasted back with their complimentary nucleotides.

EcoRI Makes Sticky Ends as it Cuts the Recognition Site
Action of EcoRI on its restriction site

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