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KVPY Sample Paper KVPY Stream-SX Model Paper-31

  • question_answer
    The diagram shows the changes in temperature of the reaction mixture during the Polymerase Chain Reaction (PCR).
               
    The main events during one cycle of the reaction are listed below.
    I. Binding of RNA primers
    II. DNA synthesis
    III. Separation
    Which combination correctly matches each event with the temperature in the reaction mixture?

    A)
    X Y Z
    I II III

    B)
    X Y Z
    III I II

    C)
    X Y Z
    II III I

    D)
    X Y Z
    III II I

    Correct Answer: C

    Solution :

    There are three major steps in a PCR
    Step 1: Denaturation
    The thermal cycler heats the mixture of primer and DNA fragment to about\[95{}^\circ C\]. Hydrogen bonds holding the double stranded DNA fragment break and the double stranded DNA separates and dissociates into single strands.
    Step 2: Annealing of primers
    The solution is allowed to cool to \[37{}^\circ C\]. As it cools primers base pair with complementary sequences at the 3' end of the single stranded DNA.
    Step 3: Primer extension
    The thermal cycler then raises the temperature to \[72{}^\circ C\]. Using the primer, the polymerase synthesises the rest of the fragment resulting in the new strand of DNA.


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