Answer
The answer is eukaryotes. Eukaryotes are organisms whose cells have a nucleus, making them more complex than prokaryotes, which lack a nucleus. Kornberg's Nobel Prize-winning work focused on eukaryotes, particularly the Kornberg enzyme, which plays a crucial role in DNA replication and the synthesis of new DNA strands essential for cell division and growth. His research advanced our understanding of the fundamental mechanisms of DNA replication in these complex organisms.