In a recombinant DNA experiment, a plasmid vector and a segment of foreign DNA are both digested with the restriction enzyme EcoRI to generate complementary sticky ends. When these fragments are mixed, they transiently pair up. Which enzyme must be added to permanently join these DNA fragments, and what specific chemical bond does it catalyze to seal the backbone?

Step-by-step solution

When DNA fragments are cut with the same restriction enzyme, they produce complementary sticky ends that can form hydrogen bonds between base pairs on their own. However, this pairing is temporary and easily broken. To permanently join the fragments and form a stable recombinant DNA molecule, the enzyme DNA ligase is required. DNA ligase seals the sugar-phosphate backbone by catalyzing the formation of a covalent phosphodiester bond between the 3'-hydroxyl and 5'-phosphate ends of adjacent nucleotides. DNA polymera