Which statement about ligase and energy is correct?

Correct answer: Energy is needed for bond formation

The governing concept is enzyme-catalysed ligation coupled to an energy source. DNA ligase joins a 3′-hydroxyl end to a 5′-phosphate end and forms a phosphodiester bond in the DNA backbone. This bond-forming reaction is not spontaneous under ordinary ligation conditions; the enzyme uses chemical energy supplied through a cofactor or activated intermediate. Depending on the ligase, the energy source may be ATP or NAD⁺, so option A is correct in general terms. Ligase does perform chemistry rather than working without a reaction. Restriction enzymes cut DNA, but energy is not used only for cutting, and ligation does not change DNA colour.