<P> Enzymes called DNA ligases can rejoin cut or broken DNA strands . Ligases are particularly important in lagging strand DNA replication, as they join together the short segments of DNA produced at the replication fork into a complete copy of the DNA template . They are also used in DNA repair and genetic recombination . </P> <P> Topoisomerases are enzymes with both nuclease and ligase activity . These proteins change the amount of supercoiling in DNA . Some of these enzymes work by cutting the DNA helix and allowing one section to rotate, thereby reducing its level of supercoiling; the enzyme then seals the DNA break . Other types of these enzymes are capable of cutting one DNA helix and then passing a second strand of DNA through this break, before rejoining the helix . Topoisomerases are required for many processes involving DNA, such as DNA replication and transcription . </P> <P> Helicases are proteins that are a type of molecular motor . They use the chemical energy in nucleoside triphosphates, predominantly adenosine triphosphate (ATP), to break hydrogen bonds between bases and unwind the DNA double helix into single strands . These enzymes are essential for most processes where enzymes need to access the DNA bases . </P> <P> Polymerases are enzymes that synthesize polynucleotide chains from nucleoside triphosphates . The sequence of their products is created based on existing polynucleotide chains--which are called templates . These enzymes function by repeatedly adding a nucleotide to the 3 ′ hydroxyl group at the end of the growing polynucleotide chain . As a consequence, all polymerases work in a 5 ′ to 3 ′ direction . In the active site of these enzymes, the incoming nucleoside triphosphate base - pairs to the template: this allows polymerases to accurately synthesize the complementary strand of their template . Polymerases are classified according to the type of template that they use . </P>

How does the structure of dna influence its function