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Question
Discontinuous synthesis of DNA occurs in one strand, because:
Discontinuous synthesis of DNA occurs in one strand, because:
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Solution
The correct option is C DNA dependent DNA polymerase catalyses polymerisation only in one direction (5′→3′)
Polymerisation of DNA by DNA polymerase:
DNA polymerase adds new nucleotides on the 3'- OH position of the previous nucleotide by a nucleophilic attack. Thus, DNA polymerase can polymerise nucleotides only in one direction, that is, (5′→3′) .
Continuous DNA synthesis:
The two strands of DNA run in antiparallel directions, one in (5′→3′)and other in 3′→5′ direction, therefore two templates provide different ends for DNA replication.
As the DNA polymerase can polymerise nucleotides only in (5′→3′) direction, continuous DNA synthesis occurs on the 3′→5′ strand or the leading strand.
Discontinuous DNA synthesis:
- The DNA strand that has polarity ((5’\rightarrow 3’)\) shows discontinuous DNA synthesis and the new complementary strand on this strand will have polarity3′→5′.
- In this case the new nucleotides need to be added on the 5' end of the new strand which cannot be done by DNA polymerase.
- Therefore, DNA polymerase synthesizes new strands in a discontinuous manner.
- Thus in the 3’ to 5’ strand (lagging strand) the synthesis of DNA is in a discontinuous manner and the newly formed fragments are called okazaki fragments.
Final answer: b. DNA dependent DNA polymerase catalyses polymerisation only in one direction (5′→3′)
Polymerisation of DNA by DNA polymerase:
DNA polymerase adds new nucleotides on the 3'- OH position of the previous nucleotide by a nucleophilic attack. Thus, DNA polymerase can polymerise nucleotides only in one direction, that is, (5′→3′) .
Continuous DNA synthesis:
The two strands of DNA run in antiparallel directions, one in (5′→3′)and other in 3′→5′ direction, therefore two templates provide different ends for DNA replication.
As the DNA polymerase can polymerise nucleotides only in (5′→3′) direction, continuous DNA synthesis occurs on the 3′→5′ strand or the leading strand.
Discontinuous DNA synthesis:
- The DNA strand that has polarity ((5’\rightarrow 3’)\) shows discontinuous DNA synthesis and the new complementary strand on this strand will have polarity3′→5′.
- In this case the new nucleotides need to be added on the 5' end of the new strand which cannot be done by DNA polymerase.
- Therefore, DNA polymerase synthesizes new strands in a discontinuous manner.
- Thus in the 3’ to 5’ strand (lagging strand) the synthesis of DNA is in a discontinuous manner and the newly formed fragments are called okazaki fragments.
Final answer: b. DNA dependent DNA polymerase catalyses polymerisation only in one direction (5′→3′)
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