Introduction to Polymerase Chain Reaction - Video Tutorials & Practice Problems

Introduction to Polymerase Chain Reaction

in this video, we're going to begin our introduction to a technique that's called polymerase chain reaction. And so when a researcher studies the DNA sequence of a specific gene and a genome, they actually need to make many copies of that gene in order to be able to study it. And so this technique preliminaries chain reaction, which is commonly abbreviated as just PCR, is a technique that's used to rapidly isolate and amplify a specific sequence of D N A. Now the term amplifies just referring to the process of making more copies of that d. N A. And so this is kind of similar to DNA cloning in a way because DNA cloning is also going to make more copies of the DNA. However, unlike DNA cloning, which is going to be using living cells to make more copies of the D. N. A preliminaries chain reaction, or PCR, is going to take place in a test tube. And so, of course, the test tube is not going to include living cells. And so we'll be able to talk more about this process of preliminaries, chain reaction and PCR. As we continue to move forward in our course. But for now, this year concludes our brief introduction to preliminaries, chain Reaction or PCR, and I'll see you all in our next video.

Why do we use PCR?

So now that we've briefly introduced preliminaries chain Reaction or PCR in our previous lesson video, it's fair to ask, Why do we use PCR? Well, it turns out that scientists will use PCR for many, many different reasons. And that's because PCR is a quick and efficient process for generating many identical copies of DNA in a test tube. Now, DNA cloning, which occurs inside of living cells and does not occur in test tubes, is going to be more accurate. But it's actually a less efficient process. And that's because, recalled DNA cloning occurs inside of cells. And although there are less mutations inside of cells, it's going to take a lot longer to amplify the D N a inside of cells. And that's because a lot of time cells take 24 hours or more to be able to grow. And then after you grow the cells, you have to isolate the D N A. And that's a whole another step within itself. And so PCR is much more quick and much more efficient. And so, in our example down below, we're going to take a look at, just in general, how PCR or what PCR can do. And so, uh, it says here that PCR can be used to amplify the amount of D N A taken from a crime scene so that a detective can actually investigate the d n A. And so down below, over here, Notice we have this scientist that has a test tube here with some DNA that perhaps was found at a crime scene. But notice that there's not a whole lot of d N A within this sample. And so notice the scientist is saying, I wish I had more of this particular DNA of interest so that he has enough DNA to be able to run tests on it. And so this is where PCR can come into play because the process of PCR polymerase chain reaction can amplify the amount of DNA to make many, many identical copies of the D N A. As we see over here. And so the scientists saying, Wow, that amplified very, very quickly. And the process of PCR can be done in a relatively short period of time, maybe something like two hours 1.5 2 hours, whereas DNA cloning again is going to take much, much longer, which it could take well over 24 hours in many cases. And so why do we use PCR to make many identical copies of D. N A N a test to very, very quickly and efficiently? And so again, as we move forward in our course, we're going to continue to talk more and more about PCR and the steps of PCR, so I'll see you all in our next video.

PCR is used to _____.

• A. Amplify a single gene or small sequence of DNA.
• B. Create DNA without introns.
• C. Insert foreign DNA into a host cell where it can be replicated.
• D. Cut segments of DNA creating complimentary sticky ends.
• E. None of these.

Components of a Polymerase Chain Reaction

So before we can talk about the details of each of the steps in preliminaries chain Reaction or PCR, its first helpful to talk about the components of preliminaries, chain reaction. And so recall from our previous lesson video that PCR differs from DNA cloning and the location that the DNA is replicated. And so PCR occurs within a test tube, whereas cloning is going to occur within a cell. And so the components that go into the test tube during PCR include, uh, these components that we have listed down below. And so the components of the PCR mixture include, uh, a here is going to be a template d n a. And so the template d n A. Is going to contain the sequence of interest for the study that the scientist is interested in amplifying and creating more copies of it. And so down below in this table on the left hand side, you can see that the components of the PCR mixture in this table, uh, corresponds with the components of the PCR mixture that we have up above in the text. And so the template D n A you can see is right here in this image down below. Now, for the second component, B uh, there are two primers that are required to DNA primers. And these two primers are going to be complementary to the opposite strands of D N A and are going to be oriented towards each other and serve as the starting 0.4. The amplification and so down below. What you can see is part B. Here are the DNA primers, which are going to be small little DNA molecules that are oriented opposite from one another. So notice that one goes from five prime 23 prime left to right and the other goes five prime 23 prime right to left. And we'll talk more about these DNA primers and exactly how they're used as we move forward. In our course now, the third component that's going to be needed is a thermo stable D n a preliminary race, and the thermo stable DNA polymerase is going to be the main enzyme that's used to synthesize the sequence of interest to amplify and make more copies of the DNA of interest and so down below. Here in the third component, see, you can see that we need a thermo stable DNA preliminaries, which is really, uh, commonly going to be a d n a polymerase called tak preliminaries, which we'll get to talk more about Tak preliminaries as we move forward in our course Now, the fourth and final component here that's going to be needed. Uh, in the PCR Uh, mixture is D here, which is going to be all four Deoxyribonucleic tides are all for DNA nucleotides that are used to synthesize DNA and so down below. Here in this image, you can see that D is going to include all four of those DNA nucleotides which you can see over here, which include, uh, these nucleotides that have the nitrogenous bases T A, C and G. And so these are the main components that are needed for a PCR mixture. Now, over here on the right hand side, what we're showing you is a little glimpse of the process of amplifying a gene with PCR. And so, of course, you're going to start off with your template d n A. Which we have here in this first column. And it turns out that PCR polymerase chain reaction actually occurs in a series of cycles And so the first cycle you can see is going to amplify the D N. A. The second cycle will amplify the D N A even more, and the third cycle will amplify the D N. A. Even more and continuous cycles will amplify the D N a more and more and more. And so there's actually a PCR formula that can be used to determine the number of new copies of template DNA that are made at each cycle. And the formula is relatively simple. It's just two raised to the power of n, where N is going to act as an exponent here, and N is just a variable that represents the number of PCR cycles. And so, for example, if we wanted to calculate the number of new copies of Template d N A. In the first cycle of PCR, all we need to do is take to raise to the power of one, since one is representing a cycle number one, and so to raise to the one is equal to two. And so notice that after the first cycle there are two new copies of DNA Now, after the second cycle, Uh, if we wanted to calculate how many new copies of template DNA that would be you just take to raise to the power of to and to raise to the power of two is equal to four. And so you can see that there are four new copies of the D. N A. After cycle number two of PCR, and the same goes for cycle number three. If we want to calculate the number of new copies of Template D N. A. You just take to raise it to the power of three, which is the number of cycles Cycle three, and to raise to the three is equal to eight. And so you can see that there are eight copies of the D N A. After cycle number three. And so we'll be able to get some practice applying these concepts that we've learned as we move forward in our course. And then later we'll get to talk about the actual steps that are involved in preliminaries chain reaction or PCR. So I'll see you all in our next video

PCR requires all of the following EXCEPT:

• A. Primers.
• B. DNA ligase.
• C. DNA polymerase.
• D. DNA of interest.
• E. Deoxyrobinucleotides.

The polymerase chain reaction:

• A. Doubles the template sequence of DNA with each cycle.
• B. Makes a single copy of the template sequence of DNA with each cycle.
• C. Is used to determine the sequence of a region of DNA.
• D. All are correct.