DNA cloning is used for a variety of purposes, but how does it work? In this video lesson, you will learn about the process of cloning DNA, as well as see examples of how cloning is used in science, medicine, and consumer products.
What Is DNA Cloning?
When you hear the word 'clone', you may think of a weird sci-fi movie, or perhaps something more realistic, like Dolly the sheep. But DNA cloning goes far beyond this. DNA cloning, which is the production of multiple identical copies of a DNA fragment, is responsible for all sorts of things, such as pest-resistant plants, bacteria used for toxic waste cleanup, and even 'stone-washed' jeans. That's right; no actual stones were used to create that look, just enzymes that are cloned from bacteria!
How DNA Is Cloned
So, how do we go from bacterial enzymes to 'stone-washed' jeans? Well, let's take a look at the steps involved in the cloning process. First, the scientist interested in cloning will isolate two kinds of DNA. One is the gene that has the DNA that will be cloned, and the other is a bacterial plasmid that will act as the carrier of the cloning DNA.
Bacterial plasmids are just small, circular DNA molecules that copy themselves separately from the other bacterial DNA material. Plasmids are ideal to use in cloning for two reasons: they are very versatile and can carry just about any gene, but they also get passed from one generation of bacteria to the next so they carry that gene on down the line.
After isolation, the scientist will treat both the plasmid and the gene of interest with an enzyme that cuts the DNA, called a restriction enzyme. These enzymes get their name from their role in nature - to restrict invading DNA from entering bacterial cells by cutting up the foreign DNA. This invading DNA may come from other organisms or even viruses, so it's important to keep them out. Amazingly, scientists know of hundreds of different restriction enzymes, though each one of them recognizes only specific DNA segments to cut.
The restriction enzyme cuts the plasmid in one place so that it creates an area that the target DNA can bind to. The target gene is cut out of its original DNA strand so that just the gene of interest is attached to the plasmid for cloning. After cutting both the target DNA and the plasmid, the two are linked together with an enzyme called DNA ligase. This pasting process results in a recombinant DNA plasmid, which is a single DNA molecule combined from two different sources of DNA. It is literally 'recombined,' hence the name 'recombinant.'
After the two DNA pieces have been pasted together, the plasmid is inserted into a bacterial cell, which will allow the bacteria to replicate and produce plasmid 'babies' that are identical to the 'parent' plasmid. Thus, our clones are born! The gene of interest can be used to produce products like plants that resist pests, proteins that dissolve blood clots in heart attack therapy, and of course, 'stone-washed' jeans for you!
Other Cloning Vectors
You may be wondering if using bacteria to produce clones is dangerous because many bacteria are harmful. While this is true, there are so many more bacteria that are not harmful, and these can easily be used for the cloning process. Bacteria also reproduce very rapidly, so they can quickly produce hundreds or thousands of clones of the DNA fragment. Bacteria are also very easy to work with in the lab, so scientists can make clones under safe, controlled conditions.
While bacteria are often the best organisms to use in DNA cloning, sometimes other organisms may be used as gene 'carriers.' The next best choice is often yeast cells, the very same yeast used in making bread and beer! Like bacteria, yeast cells are also quite easy to grow and can take up new DNA into their own. Yeast cells also have plasmids that can be used as gene 'carriers.' As cloning vectors, yeasts are used in a variety of medical products, such as the hepatitis B vaccine and cancer research.
Sometimes, only very specific cells can be used in cloning. Mammals make a variety of proteins, one of which is called a glycoprotein. This is a mammalian protein with chains of sugars attached to it. Only mammalian cells can attach the sugars in the right way, so other mammalian cells have to be used for cloning these types of proteins. These proteins are important because they're used to produce treatments for things like anemia and blood transfusions.
There's almost no limit to the possible uses of DNA cloning, which is the process of making multiple identical copies of a DNA fragment. By cutting out the desired gene along a DNA strand with restriction enzymes, and pasting it into a bacterial plasmid with DNA ligase, the desired gene can be quickly and easily copied through bacterial reproduction.
The recombinant DNA plasmids pass the genetic information along through each successive generation, making bacteria ideal for 'carrying' genes through the cloning process. While bacteria are the most commonly used cloning vector, other types of cells, such as yeast and mammalian cells, can also be used. Using these types of cells may allow for the cloning and production of proteins that simply can't be produced using bacterial cells.
Once this lesson is over, you should be able to:
- Define DNA cloning
- Summarize the steps of the cloning process
- Explain why bacterial plasmids are used to aid in cloning
- List some of the other organisms that scientists use as cloning vectors
- Provide examples of how DNA cloning is used in various industries