The names of basic enzymes often make it onto the exam (kinase, endonuclease, carboxylase etc). You need to keep an eye out for the enzyme types that keep coming up and make sure you can define their function. A 'ligase' is an enzyme that joins to biomolecules together through formation of a new chemical bond. DNA ligase. In forming circular DNA, DNA ligase catalyzes the formation of a phosphodiester bond between the 3'-OH at one end and the 5'-phosphate at the other.