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Consider the two double-stranded DNA fragments produced after the digestion of a linear DNA molecule by a specific enzyme: Fragment I: 5^ - G -3^ 3^ - CTTAA -5^ Fragment II: 5^ - AATTC -3^ 3^ - G -5^ Which of the following statements is correct regarding the original intact DNA sequence and the enzyme involved?

Options

  1. AThe enzyme involved is an exonuclease that removes nucleotides from the free ends to create these fragments.
  2. BThe enzyme is an endonuclease that recognises the palindromic sequence 5^ - GAATTC -3^ and cuts away from the
  3. CThe original intact sequence was 5^ - GATATC -3^ and the enzyme produced blunt ends.
  4. DThe enzyme cuts the DNA exactly at the centre of the palindromic sequence to generate these overhanging stretc

Correct answer

B. The enzyme is an endonuclease that recognises the palindromic sequence 5^ - GAATTC -3^ and cuts away from the

Step-by-step solution

By aligning the complementary overhanging stretches (sticky ends) of Fragment I and Fragment II, the original intact DNA sequence can be reconstructed as 5^ - GAATTC -3^ on one strand and 3^ - CTTAAG -5^ on the complementary strand. This specific palindromic sequence is recognised by the restriction endonuclease EcoRI. Restriction endonucleases make cuts at specific positions within the DNA, unlike exonucleases which remove nucleotides from the ends. EcoRI cuts the DNA between the bases G and A on both the strands.

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