Final answer:
DNA exonuclease converts sticky ends to blunt ends by trimming off the overhanging nucleotides. This process makes it possible for DNA fragments to be ligated together without relying on base pairing, although it may be less efficient than ligation of sticky ends.
Step-by-step explanation:
How DNA Exonuclease Converts a Sticky End to a Blunt End
To understand how DNA exonuclease converts a sticky end to a blunt end, it is essential to first grasp the natures of these two types of ends. Sticky ends are DNA sequences produced by restriction enzymes like EcoRI and HindIII that cut DNA asymmetrically, leaving overhangs with unpaired nucleotide bases. These exposed bases can form hydrogen bonds with complementary sequences, which are key to the process of DNA recombination. When a different enzyme, a DNA exonuclease, acts on these sticky ends, it systematically removes nucleotides from the end of the DNA strand. If the exonuclease removes nucleotides from the overhung (protruding) single-stranded part of a sticky end, it can transform this overhang into a more stable blunt end, which no longer has overhanging nucleotides at its terminus. Blunt ends may be less efficient at annealing than sticky ends because they lack the hydrogen-bonded 'cling' of overhangs, but they can still be ligated together by an enzyme called DNA ligase.
Recombinant DNA (rDNA) technology often utilizes sticky ends created by restriction enzymes for the purpose of ligating different DNA sequences together. By using a DNA exonuclease to convert the sticky ends into blunt ends, two DNA fragments that were not originally capable of easily annealing due to sequence mismatch can be made to ligate together without base pairing between overhangs.