The enzyme responsible for "unzipping" the DNA double helix is helicase. Helicase is involved in DNA replication and breaks the hydrogen bonds between complementary base pairs, causing the two strands of the DNA molecule to separate and unwind. This process is essential for DNA replication, as it allows the DNA polymerase to access the template strand and synthesize a new complementary strand. RNA polymerase, on the other hand, is responsible for unwinding the DNA during transcription, but it does not break the hydrogen bonds between the two strands.