
220 ◾ Biological Computation
since they allow cutting DNA for many purposes such as introducing
new sequences into existing DNA molecules. Hundreds of restriction
enzymes are currently available commercially.
5.1.4 Ligation
Ligase enzymes can repair breaks in one of the strands of a DNA mol-
ecule (provided that the molecule is held together by its double-strand
structure). is is done by bonding (ligating) adjacent nucleotides, thereby
recovering the original structure of the molecule (Figure 5.4). Ligase
enzymes are used by cells both in DNA repair and in DNA replication. In
molecular biology, ligase and restriction enzymes are oen ...