2) Annealing

Jason Amores Sumpter
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in this video, we're going to talk more about the second step of each PCR cycle, which is a kneeling. And so in this second step, the DNA primers are actually going to a kneel to the heat denatured single stranded DNA. And so, in this second step of PCR, a kneeling of the DNA primers to the heat denatured single strand of D N A. Is going to occur, and so the temperature is going to be lowered down to about degrees Celsius. And so, if you recall and step number one, the temperatures were as high as 95 degrees Celsius, and so there is a significant drop from 95 degrees Celsius down to about 55 degrees Celsius. And so that's lowering the temperature. And this lowering of the temperature allows for complementary base pairing. And so the complementary base pairing is going to occur between the DNA primers and the single stranded DNA itself. Now attack preliminaries, uh, is actually going to remain inactive at these cooler temperatures because the temperatures are just too cool or too cold for it to synthesize DNA. And so when we take a look at our image down below, Over here on the left hand side at the second step a kneeling. What you can see is that the temperatures are going to be cooled, so cooler temperatures are going to allow the DNA primers to a kneel to the d N A. And so, after the first step of PCR, which is going to be denatured aeration, we know that we have generated single stranded DNA, this heat, denatured DNA. And so in the second step, the temperatures are cold so that the DNA primers can a kneel to the d n A. As we see here and notice that they are kneeled on different DNA strands and they are kneeled, facing towards each other in terms of their five prime and three prime ends. This one goes from left to right, and this one goes from right to left facing towards each other. And so now that these DNA primers have been a kneeled, uh, and the third step, they can be extended. However, it cannot be extended here in the second step because these temperatures of degrees Celsius are just too cold for the tack preliminaries to work. And so notice the tactile memories is saying, Burr. I can't work like this and he's all cold. And he can only work when we increase those temperatures just a little bit to the right temperatures. And so this year concludes our brief introduction to the second step of PCR, a kneeling of the DNA primers, and we'll be able to talk about the third and final step of PCR in our next video.