Final answer:
The process that results in an exact copy of the original DNA strand in the nucleus is DNA replication, a semi-conservative process involving enzymes like DNA helicase and DNA polymerase.
Step-by-step explanation:
The process that occurs in the nucleus of the cell and results in an exact copy of the original DNA strand is known as DNA replication. During DNA replication, a variety of enzymes, including DNA helicase and DNA polymerase, work together to unwind the DNA molecule, separate the two strands, and then synthesize new complementary strands along each parent strand. Consequently, each new daughter DNA molecule consists of one original strand and one newly synthesized strand, making this a semi-conservative process. DNA uses this exact replicating mechanism to ensure that when a cell divides, each new daughter cell receives an identical copy of the organism's genome.