The essential molecular structure for DNA replication is the double helix. This structure consists of two strands that twist around each other, held together by complementary base pairs. During replication, the strands separate, and each serves as a template for creating a new complementary strand, ensuring accurate duplication of the genetic material. The enzyme DNA polymerase plays a critical role in adding nucleotides to form the new strand, making the double helix essential for passing genetic information during cell division and reproduction.