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Benefits of cycling
Polymerase Chain Reaction (PCR)

Polymerase Chain Reaction (PCR)

Polymerase chain reaction, or PCR, uses
repeated cycles of heating and cooling to make many copies of a specific region of DNA. First the temperature is raised to near
boiling, causing the double-stranded DNA to separate or denature into single strands. When the temperature is decreased,
short DNA sequences known as primers bind or anneal to complimentary
matches on the target DNA sequence. The primers bracket the target sequence to be copied. At a slightly higher temperature, the
enzyme taq polymerase, shown here in blue, binds to the prime sequences and adds
nucleotides to extend the second strand. This completes the first cycle. In subsequent cycles, the process of
denaturing, annealing, and extending are repeated to make additional DNA copies. After three cycles, the target sequence
defined by the primers begins to accumulate. After thirty cycles, as many as a billion
copies of the target sequence are produced from a single starting molecule.

88 comments on “Polymerase Chain Reaction (PCR)

  1. @zanderez
    No, its DNA strand which is being separated. RNA is usually single stranded. Remember simple rule? DNA is used to make RNA, which in turn, is used to make proteins.

  2. ok how do you make the primers, do you add A T G C in a sequenced mix in test tubes and heat treat to cause them to bind into the gene sequence that you want? how do we know that the right genes are being targeted, because at some point the A T G C repeat at different parts along the DNA strand, this process cannot directly find the genes, im guessing its multiple processes after the target strand is found so you take the smaller part and then subdived off of that to get precise gene pieces.

  3. @watashiwaka19501 i know that there are viral cutters and mending chemicals that chop up dna and push it together, because thats the same mechanisms that viruses use to hijack your cells, but from this process i think it has to have more than one PCR step to target more precise gene sequences. great video but i think some more important parts are not shown, yea there is got to be more to this, i wonder what the primers and polymerase steps are called.

  4. @wallacemail @zackboomer Discussing on the internet is like winning the paraolympics, even if you win, you are still retarded.

  5. Had a lot of fun with the comments, ( I'm bilingual too ) – a very nice distraction from learning for biology und biologie =) Anyways, a very good video that helped me a bit more to understand the PCR, even if it was not very detailed. Thank you for that!

  6. @ForYeensSake Wow that's a new one. I probably have only heard that one about 4389747239374893 times since I started using the Internet.

  7. @zackboomer you probably did because you replied. But keep thinking you're a cool dude because you don't care about stupid stuff like languages.

  8. what happens to the original DNA strand that contains genetic sequences that are no longer needed? do they remove it through gel electrophoresis?

  9. As a student in Cellular Physiology, let me just say… finding a sequence you can actually do this to is a bitch.

  10. From what I understood, two types of primers are used, one that tells where to start copying and one that tells where to stop. Both of these have multiple particles though, you need individual particles of each of the two primers for each copy of the target sequence. Either that, or the primers detach from the finished copy of the target sequence and go copy another.

  11. the single strands at the beginning each have different sequences of bases. you need two sets of primers to bind to each one. you add the primers in excess though to make sure that the primers bind. pcr usually stops when the primers run out and you can either add more primers and continue the process or stop there.

  12. There are 2 primers for each target sequence: forward and reverse. Since they are each in the forward and reverse direction, they act kind of like parentheses in the DNA for amplification.

  13. It sounds like you understand this stuff pretty well. Assuming you've determined the target sequence you want to amplify, how does one determine which two primers to use?

  14. Depending on the sequencing machine downstream that you will use, the gc content of the amplicon, different computational softwares will pick the perfect pair of primers about 20 base pairs long compatible in melting temperature for amplification.

  15. If you know the sequence of DNA that you are trying to amplify then you can design a primer to specifically bind to that sequence, by have bases that are complimentary. It just requires knowledge of the sequence first.

  16. What prevents the single stranded DNA from sticking to each other when the Temperature was lowered for the attachment of the primers?

  17. This video is by far the best PCR video I have seen. Incredible work and accuracy impart of the people that dedicated their time for creating this animation.

  18. A little note: the annealing temperature is usually chosen between 40-60°C. There are a few factors that influence the annealing temperature. An important factor is the fact that G-C binding involves 3 hydrogen bonds (rather then 2 hydrogen bonds at A-T binding). Because of these 3 hydrogen bonds, the more G's en C's are in the primer, the stronger it will bind to its complementary sequence on the template DNA. Therefore higher annealing can and must be used when the primer contains lots of G & C. (The annealing temp. can even go up to 72°C if you have a high G-C content)

  19. Dude, love the video!  I’m always looking for some good hip hop and it can be pretty tough to find.  You should check out this other artist I just got really into, "Hunnid"  I have some of his videos on my page!

  20. this might be an ignorant question but… does this mean cloning is possible using this concept?? i mean like building off from this concept

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