Much like the insulation around the wires in electrical systems, glial cells form a membraneous sheath surrounding axons called myelin, thereby insulating the axon. This myelination, as it is called, can greatly increase the speed of signals transmitted between neurons (known as action potentials).
DNA ligase is an enzyme that connects nucleotides of DNA from the phosphate to the sugar. This seems to match the provided description, therefore I believe it to be the correct answer.
