DNA helicase is an enzyme that plays a crucial role in DNA replication and transcription. It is a type of biological molecule that breaks the hydrogen bonds between complementary bases in DNA to expose the template strand of DNA ready for transcription. Helicases are molecular motor proteins that harness the chemical energy of ATP hydrolysis to break the hydrogen bonds between the nitrogenous bases of DNA, leading to their separation and allowing other enzymes to copy the DNA sequence. Helicases promote the opening of the DNA helix, separating it into two single strands to make replication occur. Thus, DNA helicase is an enzyme that unwinds the double-stranded DNA helix, usually used for DNA replication. In summary, DNA helicase is an enzyme, which is a type of biological molecule that plays a crucial role in DNA replication and transcription.