Replication in Eukaryotes

Most prokaryotic factors used during replication have equivalents that play similar roles in eukaryotic DNA replication.

This process starts at an origin of replication, where a recognition complex binds.

Helicase then moves to the site and separates the DNA strands, creating a replication bubble with two forks.

Primase then synthesizes short RNA primers. As helicase moves forward, DNA polymerase extends the primers by adding complementary DNA nucleotides in the 5-prime-to-3-prime direction.

As in prokaryotes, the newly formed leading strand grows continuously, following the replication fork.

The lagging strand forms short Okazaki fragments that grow in the opposite direction of the replication fork. Because of the structure of the replication bubble, the DNA template that supports leading-strand synthesis on one side supports lagging-strand synthesis on the other side.

Several origins of replication are present on a linear eukaryotic chromosome, and replication ends when neighboring replication bubbles merge. RNA primers are then removed by RNase. The DNA polymerase fills the gap with DNA. DNA ligase then joins the remaining DNA segments.

When the final primer is removed from the lagging strand, a gap remains, leaving a short stretch of the DNA template uncopied. To solve this problem, an enzyme called telomerase binds to the overhanging region and extends it with a non-coding DNA sequence.

Then, primase adds a short primer sequence, and DNA polymerase extends the region, forming a telomere that protects against the loss of coding DNA on the lagging strand during repeated rounds of replication.

So, eukaryotic DNA replication produces two DNA molecules, each made up of one parental strand and one newly synthesized strand. It uses multiple origins of replication and telomeres to duplicate the entire chromosome.