Polymerase Chain Reaction (PCR) | Biotechnology: Principles & Processes Part 7 | Biology Class 12

The topic of this presentation is polymerase chain reaction, in short aka PCR first, the meaning oc PCR polymerase chain reaction, the word used is polymerase recall the enzyme DNA polymerase what is function of DNA polymerase? it synthesizes copies of DNA it forms copies of DNA from one DNA in the same way, we use this chain reaction when we have a very little DNA sample even if only one DNA strand is available with us then we can synthesize multiple copies of that single strand using this reaction such a technique is known as polymerase chain reaction in this presentation we will discuss procedure and applications of polymerase chain reaction first, we will discuss some important terms which will help us understanding this topic first term is PCR primer we use primers in PCR these are synthetic oligonucleotides and are short fragments of single stranded DNA these short fragments show complimentarity with a small region of template DNA we will understand this thing a in better way when we will discuss PCR what could be its use it is mentioned here that it shows complimentarity with to DNA sequences that flank the target region of interest. what does it mean for example we have a human DNA strand and we are not interested in the whole strand we require only insulin gene from that strand we want to amplify only insulin gene then with the help of primer we can locate insulin gene on that whole DNA strand we will understand this point better when we will discuss PCR procedure first, we are able to locate our target gene with the help of primer and second thing is, primers provides a “free” 3′-OH group to which the DNA polymerase can add dNTPs in order to amplify that DNA strand one more point here, the DNA polymerase we use in the technique is not at all a normal DNA polymerase we extract it from a special kind of bacteria this bacteria is Thermus aquaticus that grows in hot spring (90°C). a natural hot spring is shown here in this picture the temperature of these hot springs could reach up to 90 degree Celsius it lives in such hot waters the DNA polymerase which is extracted from Thermus aquaticus known as Taq polymerase T stands for Thermus and aq stands for the species name aquaticus thus Taq polymerase is derived from bacteria Thermus aquaticus which lives in hot springs we use this special kind of polymerase in PCR now we will discuss procedure of PCR with the help of this diagram a DNA strand is shown here some grey region is shown here and this the blue portion grey portion signifies that DNA strand might continue both side , it could be a very long DNA strand out of this long DNA strand we are interested only in this small blue DNA portion because it is our desired gene DNA this is the first thing now recall DNA replication during DNA replication, first step is breaking of hydrogen bonds between the base pairs and formation of replication fork this step is done artificially on higher temperature we will put this DNA at 95 degree temperature hydrogen bonds break at this high temperature and this duplex will be converted into single stranded DNA and this process is called Denaturation now the second step is to add primers now we will add primers to such denatured DNA and the mixture will be cooled down to 50 to 70 degree at this temperature primers will attach themselves to the template DNA as per their complimentarity and this process is called Annealation anneal means to join as these primers are joined to the template strand therefore this step is called Annealation next step is extension one more important point here you must be observing the application of primer that with the help of primers we locate our target gene this blue region DNA is our target gene we have designed primer accordingly and have synthesized accordingly which are complimentary to the flanks of this desired gene in this way we locate our desired gene next step is extension now in this mixture of DNA combined with primer now we will add Taq polymerase and deoxyribonucleotides Taq polymerase will now synthesize a new strand using these deoxyribonucleotides on the template DNA it will synthesize new DNA following complimentarity as a result we will get two DNA strand from a single one here we have shown one cycle only when we repeat this cycle as a result we will get multiple copies after some cycles as we shown here here that we get more that 20 lakh copies after 20 cycles if we run 30 cycles, then we get more than one billion copies of DNA one more important point I want to tell here see this diagram obverse this primer this primer is attached to this location now, when Taq polymerase enzyme will start its work from this location then it will exclude this DNA, but it will continue in this direction to the end of this strand and the other Taq polymerase which will work on this location then it will exclude this grey portion and will polymerize the whole strand in this direction but we told you that we can exclusively amplify our desired gene with the help of primer in the process called PCR then how it will be done to understand this point watch this video Link of animation video of PCR is available in the description box this is an animated video of PCR in this video it is very well shown that after some cycles , only target gene will be amplified during PCR now we will discuss Applications of PCR it is used the most in forensic science for DNA fingerprinting if we have collected a sample of blood or semen, a hair root this could be a very important evidence and we could collect only a very little amount of DNA from this sample the first step is to amplify this DNA and now use this DNA for further investigation so we use PCR in Forensic Science for DNA fingerprinting second use is Detection and diagnosis of infectious diseases PCR can detect presence of pathogen at very early stage a very good example is AIDS during window period of AIDS window period- when symptoms are not seen and if we conduct ELISA or western blot during window period the these test show negative results because levels of antigens and antibodies are not sufficiently high to be detected by these diagnostic tests PCR can detect presence of HIV even during window period because it is highly sensitive technique with the help of which we can detect HIV even during window period the blood we use for blood transfusion we can detect presence of some pathogen in that blood from example pathogen of tuberculosis which is not detected easily we can detect presence of such pathogens easily with the help of PCR next is – Detection of infection in the environment we can test water sample for presence of some particular pathogen we use PCR in research work we have already seen that how we can amplify insulin gene from a single DNA strand the insulin gene which we are using for some genetic engineering program we also use PCR in archaeology as we get very little amount of DNA from fossils before studying that DNA it is essential to amplify that little amount of DNA avilable with us so these are some of the Applications of PCR


  1. Akki Jataim said:

    pleas sir making in Application of biotechniches

    November 1, 2017
  2. Brij Singh said:

    It very helpful for me to know about pcr.
    Please describe rt-pcr work and application

    November 1, 2017
  3. qayam sk said:

    Southern and nouthern par bhi. Aisa hi lecture banaye mam

    November 2, 2017
  4. jay s YADAV said:

    plz human physiology ke lec. uplod kr do…

    November 2, 2017
  5. the rock said:

    Thank you so much mam

    November 3, 2017
  6. kritikl kushwaha said:


    November 4, 2017
  7. Sapna gaud said:

    Wow…mam this video is very nice..i understand well..thank you..😊

    November 6, 2017
  8. Kapil Ghidode said:

    Thankuuu so much mam

    December 11, 2017
  9. Muhammad Shahbaz said:

    v nice lacture mam

    December 17, 2017
  10. Priti Shah said:

    Thank you so much ma'am it was very much helpful

    December 29, 2017
  11. Rajendra Pratap singh said:

    Wow madam kitna ache se smj aaya is video se

    January 18, 2018
  12. SUNIL KUMAR said:

    thanks for making such a nice video

    February 6, 2018
  13. Shekhar Gautam said:

    Please make a video on grastulation

    February 20, 2018
  14. Angel's wings said:

    Thanx mam 4 this helpful explaination πŸ˜ŠπŸ˜ŒπŸ’›πŸ’›

    March 3, 2018
  15. TacnO neGY said:

    thNQ maM


    March 13, 2018
  16. Ashraf Khan said:

    Best description ever !!!

    March 23, 2018
  17. vasu music vines said:

    Such a very useful and great vid. About this amazing topic πŸ‘ŒπŸ‘Œ

    April 3, 2018
  18. Videoz Shop said:

    how pcr detect infections?

    May 3, 2018

    Thanks mam….Jo aap hindi me padate h

    May 17, 2018
  20. Yashraj Verdhan said:

    Mind boggling lecture mam πŸ‘Œ

    June 9, 2018
  21. Vishal Khadse said:

    Mam, I had been hearing, parent DNA and offspring DNA gated tested in the PCR machine is it? And how, because hear as doing pcr machine job DNA copied, ……. How tell me

    July 16, 2018
  22. singh singh said:


    August 11, 2018
  23. Mahima Naik said:

    Thank you sooo much mam. ….mera kal seminar hai ess topic par bohot easy language main aapne describe kiya hai.Maine bohot videos dekhe bt samaj main hi nhi aa raha tha. …….thank you soo much for simplifying the PCR Technique πŸ˜™πŸ‘πŸ‘πŸ‘πŸ‘

    October 10, 2018
  24. Usama Rajpoot said:

    ❀️Nice mam

    October 15, 2018
  25. Laxmi Dhungel said:

    best lectur ever…

    November 22, 2018
  26. Amirul Hassan said:

    Nice vedio

    January 7, 2019
  27. zh vlogs said:

    very much informative. very easy. one thing i could not got is…….. how elongation beyond desired length is blocked. they told some link but i could not find that. they guide to go for that in DESCRIPTION BOX. i dont know how to go there. please send me that link on [email protected] m

    January 9, 2019
  28. Noor Khitab said:

    practically dekhayaaaa naaaa

    January 14, 2019
  29. Rushda Haq said:

    very nice explanation ma'am

    March 20, 2019
  30. Concept Tutorial said:

    Follow the link for Complete Chapter Notes:


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    May 5, 2019

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