in this video, we're going to talk about the third and final step of each PCR cycle, which is extension. And so the final step of PCR, which is this third step, is the extension of the new DNA strand by the thermo stable tack prelim a race. And so the temperature in the third step is going to be changed. An increase from 55 degrees Celsius in the second step to about 72 degrees Celsius here in the third step. And the 72 degrees Celsius is an ideal temperature for the activity of the tech preliminaries. And so the tact polyamorous is going to incorporate deoxyribonucleic tides and or those DNA nucleotides and use them to extend the DNA primers on each strand of the DNA making two identical copies of the D. N A. And so if we take a look at our image down below at this third step here of the PCR uh, cycle extension, which will notice, is that over here on the left, we're starting off with what we ended within the second step, which is the a kneeling of those DNA primers. And so here in the second step, the temperature is going to be increased to the ideal temperature for tact. Kolyma race. And so the attack preliminaries is able to incorporate the DNA nucleotides the free DNA nucleotides and use those free DNA nucleotides to extend each of the primers. And so you can see that the extension of the primaries is always going to be in the five prime 23 prime direction. And so the tactile memories will extend this and this direction. And the tactile memories here will extend this primer in this direction from right to left. And so the tack preliminaries extends the new strands of D N A. Until we have the template d n A. Which has been replicated. So the template d n A. Has been replicated here. And so you can see that the original we now have two identical copies of the original template D N A. And so that is going to conclude this third and final step of each PCR cycle. And so after, uh, the third step has been completed, then it can go back into a new cycle of PCR, where each of these products from the first cycle can be used as reacted in the second cycle and so on. And so this year concludes our introduction to the third step of PCR extension, and we'll be able to get some practice applying all of the concepts that we've talked about as we move forward in our course, So I'll see you all in our next video.