DNA Replication | Molecular Basis of Inheritance Part 7 | Biology Class 12 | Hindi
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DNA Replication | Molecular Basis of Inheritance Part 7 | Biology Class 12 | Hindi

topic of this presentation is DNA replication please watch our video structure od DNA berfore watching this video to understand DNA replication in a better way first of all we will discuss about Enzymes which play important role in DNA replication and catalyze this process DNA polymerase is the main enzyme It catalyses the polymerization of deoxynucleotides on the parental DNA template. that’s why this enzyme is called DNA-dependent DNA polymerase as it uses parental DNA template to synthesize new DNA strand second enzyme is called Helicase It unwinds the DNA strand to form the replication fork. it breaks hydrogen bonds between base pairs to unwind double strand of DNA third enzyme is DNA ligase okazaki fragments are formed during this process DNA ligase joins the Okazaki fragments here we have used some terms which our students might not have heard about yet like replication fork, okazaki fragments and lagging strand we will discuss all these terms in detail ahead in this presentation we will now discuss some Rules which are followed during DNA Replication first rule is that DNA replication is semi-conservative we will discuss this point ahead in this presentation second rule is – DNA replication does not start randomly form anywhere on DNA strand DNA strand has some already defined points – unique points – from where replication starts those points are called origin of replication or in short we call them ‘ori third important rule is that DNA polymerase shows directional activity it always catalyses polymerisation only in one direction (5’ to 3’) knowing these rules ease the understanding of DNA replication we will discuss semi-conservative replication with the help of this diagram we have shown a parental DNA here in the diagram double strand of parental DNA is shown by now we have learnt that double strand unwinds during replication after unwinding, a new strand will be polymerized on the old strand it means that during replication when two DNA strands are forming from one strand then in new DNA double strand one strand is parental while the other is the new one such phenomenon is called semi-conservative synthesis the synthesis in which old strand is conserved- preserved and a new strand is formed this phenomenon is called semi-conservative DNA replication now we will learn what are Replication Bubbles by now we have learnt that DNA replication does not starts randomly there are some defined points on a DNA strand which are called origin of replication and one DNA strand can have more than one origin of replication replication always starts from these points unwinding of DNA starts from origin of replication we will see these bubble like structures after unwinding of DNA strand at these points of origin these are called Replication Bubbles when a new DNA is formed, these bubbles proceed in both the directions as a result we will get two daughter DNA strands from one parental DNA strand so we have made our student understand the concept of replication bubble with the help of this diagram we will learn about Replication Fork with the help of this diagram by now we have understood what replication bubbles are now visualize that this bubble is broken in the middle like into two parts like this and now we have rotated one half of this bubble by 90 degree so we get this kind of structure this is the diagram you see in most the text book and this is called Replication Fork I just want to make my students visualize that what the replication fork is and it is formed replication fork is never formed at the ends of a DNA strand DNA replication starts somewhere from the interior points we represent replication bubble in the form of fork just for the sake of convenience and simplicity we have learnt about replication fork with this diagram we have learnt enough concepts to understand the process of DNA replication now we can easily understand the process of DNA replication by now we have understood what the replication bubble is what the replication fork is parental DNA has underwent unwinding whatever we have discussed by now, we will apply all those concepts in this diagram semi-conservative DNA Replication is shown as this is the parental strand on which new strand is formed but I am observing some unique thing in the diagram that one strand is synthesized in this direction whereas the other strand many small fragments are proceeding in the opposite direction why is this happening this is happening because – I want to recall one rule that that DNA replication always proceeds from 5′ to 3′ direction we have to follow this rule we also have to follow the rule of anti-parallel orientation what is anti-parallel orientation if one strand runs fro 5′ to 3′ direction then the other strands runs from 3′ to 5′ direction as you can see here that this is a parental strand which runs fro 3′ to 5′ now, the new strand that will be formed on this parental strand will run from 5′ to 3′ it means that we have follow two rules – anti-parallel orientation and 5′ to 3′ proceeding on this strand the parental strand which runs from 3′ to 5′ direction polymerization is occurring in usual manner on this strand but the parental DNA which runs from 5′ to 3′ direction, we will see some unusual process here now visualize that replication bubble is proceeding slowly in both the direction and DNA polymerase which is working on this strand catalyze the process in opposite direction in order to follow the rules that’s why numerous small fragments are formed in the opposite direction on 5′ to 3′ parental strand that’s why these small fragments are formed in the opposite direction whereas a continuous strand is synthesized on 3′ to 5′ parental strand and this strand is called a leading strand whereas the small fragments which are formed in the opposite direction on 5′ to 3′ parental strand these are called okazaki fragments so continuous polymerization occurring on 3′ to 5′ strand, it is called continuous synthesis whereas polymerization occurring in small fragments on 5′ to 3′ strand, it is called dis-continuous synthesis now DNA ligase about which we have already discussed DNA ligase joins these okazaki fragments it means that DNA ligase plays no role in continuous synthesis DNA ligase plays its role in discontinuous synthesis only joining the okazaki fragments these fragments are called lagging strands we have also shown helicase in the diagram Helicase keeps unwinding the DNA strand to form the replication fork during DNA replication exposing the base pairs some small bead like structures are also shown in the diagram these are single strand stabilizing proteins the exposed bases on the single strands of DNA have tendency to form pairs again as these these are complimentary base pairs therefore these base have tendency to form hydrogen bonds again DNA replication cannot proceed if this happens these stabilizing proteins mask the expose bases on single strands of DNA and prevent formation of hydrogen bonds between them so we have discussed DNA replication we have summarized differences between leading and lagging strands in this table this table is very important for students who are preparing for board exams

80 thoughts on “DNA Replication | Molecular Basis of Inheritance Part 7 | Biology Class 12 | Hindi

  1. Mam can you explain me that why DNA polymerase catalyses polymerisation only in one direction i.e., 5' to 3' ??

    if possible please reply me now

  2. very awesome video,amazing and outstanding. loved it very much it helped me a lot
    thank u veryyyy much mam.

  3. m frm Pakistan n i want to salute all indian science teachers … they demonstrate any topic very well… thanx mam..

  4. mam pls make video on biotechnology biology in human welfare and evolution as early as possible because I have an exam on 1 September

  5. your videos are very understanding nd i think before that I should leave this chapter because it is so typical thanks a lot mam I needed a teacher like you

  6. mam u didnt mention RNA primer which is formed to start the replication . RNA primer is also formed for the synthesis of Okazaki fragments

  7. I am from Pakistan and it is awsum video because I understand each and every step in DNA replication very clearly thank you….

  8. Mam plz ap mutation ke topic pr video banae complete explaination kyun ap ki explain karne ka tarika brilliant he plz plz request mam……

  9. thank u so much wese to hamri clg mem ne bohot ache s clr kar diya tha but kuch basic.. sikhne ko or riwise ho gya ….thanks.. very nise

  10. Thank you mam…..I am in class 10…and I want to learn how DNA copying work……could….u plz…..understand me……thank you

  11. दिल से धन्यवाद दिदी आपको, आपका समझाने का तरिका का जवाब नहीं हैं,

    I love u DIDI

  12. mam bhout acha explanation tha thankuuu muzze 25 out off 23 max mile vo bhi aap ke explanation se thanku so so much mam

  13. Mam I m a Pakistani.
    I understand you lectures well !!!
    I really salute u👮
    4 your efforts 4 students!!…💓💓🌷🌷

  14. Follow the link for Complete Chapter (Molecular Basis of Inheritance) Notes

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