Why do eukaryotes have multiple origins of replication

Topic: Dna Replication. Key Terms Origin of replication : A particular sequence in a genome at which replication is initiated. Prokaryote : Single-celled organisms that lack membrane-bound organelles. Eukaryote : Organisms with membrane-bound organelles. Helicase : an enzyme that unwinds the DNA helix ahead of the replication machinery Replication fork : It is a Y-shape structure formed due to the unwinding of the DNA at the origin of replication.

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Free Trial Session Enrollment. You are subscribed. Subscribe Now. Trial Session Enrollment. The Next Class:. Enter Session. Enroll in course. Welcome Back! Considering the size of eukaryotic chromosomes, this is necessary to finish complete replication in a timely manner. Each of these origins defines a replicon , or the stretch of the DNA that is replicated from a particular origin. The replicons do not replicate at exactly the same time although all within the same phase of the cell cycle, see chapter 15 , so it is important to make sure that replicons are used only once during a cell cycle.

Eukaryotic cells alternate between growth and division, and DNA is replicated during the growth phase. Another enzyme, helicase, first separates the two stands in a region called a replication origin. Each strand serves as a template for a new strand with a complementary sequence of nucleotide bases. A replication bubble surrounding the polymerase molecule moves along each DNA strand during the copying operation. The old and new strands zip together at the rear of the bubble.

DNA polymerase can transcribe eukaryotic chromosomes at a rate of about 50 base pairs per second. If the chromosome had but a single origin of replication, it would take about a month to copy one DNA helix. By using multiple origins, the cell can replicate a helix in about an hour, a fold speedup. During the process, multiple replication bubbles on each chromosome churn out small lengths of DNA that are then spliced together to form the finished product.

The advantage of multiple origins is that it allows relatively rapid cell division and organism growth.