DNA replication is a vital process by which a cell makes an exact copy of its DNA, ensuring that genetic information is accurately passed on to daughter cells during cell division. This process is fundamental for growth, development, and maintenance of all living organisms. While the core mechanisms of DNA replication are similar across all life forms, there are some notable differences between prokaryotes and eukaryotes, reflecting their distinct cellular structures.

In prokaryotes, such as bacteria, DNA replication occurs in the cytoplasm due to the lack of a defined nucleus. The DNA is typically in the form of a single circular chromosome. DNA replication in prokaryotes is relatively simple and begins at a single origin of replication, where the DNA helicase unwinds the DNA, and the DNA polymerase enzyme synthesizes a new strand complementary to the template. Prokaryotes have a faster replication process because of fewer regulatory steps and the absence of complex cellular structures like the nucleus.

In eukaryotes, DNA replication occurs within the nucleus and is a more intricate process due to the presence of multiple linear chromosomes. Eukaryotic DNA is wrapped around histone proteins, forming chromatin, which must be unwound before replication can begin. Eukaryotes have multiple origins of replication on each chromosome, and replication is more tightly regulated. The process involves several key enzymes, including helicases, DNA polymerases, and ligases, along with various checkpoints to ensure accurate replication. This complexity reflects the larger amount of genetic material and the need for precise control to maintain genomic stability in eukaryotic cells.

Both prokaryotic and eukaryotic DNA replication rely on the principle of semi-conservative replication, where each new DNA molecule consists of one original strand and one newly synthesized strand. Despite differences in the process, the underlying mechanisms of DNA replication are highly conserved across all domains of life. In this chapter, we will explore the experimental evidence that demonstrated semi-conservative replication, and examine how DNA is replicated in both prokaryotes and eukaryotes.