![]() Helicase and other proteins are then recruited to start the replication process ( Table). At the origin of replication, a pre-replication complex is made with other initiator proteins. The chromatin (the complex between DNA and proteins) may undergo some chemical modifications, so that the DNA may be able to slide off the proteins or be accessible to the enzymes of the DNA replication machinery. Histones must be removed and then replaced during the replication process, which helps to account for the lower replication rate in eukaryotes. Eukaryotic DNA is bound to basic proteins known as histones to form structures called nucleosomes. Before replication can start, the DNA has to be made available as a template. The essential steps of replication are the same as in prokaryotes. They are known as pol α, pol β, pol γ, pol δ, and pol ε. The number of DNA polymerases in eukaryotes is much more than in prokaryotes: 14 are known, of which five are known to have major roles during replication and have been well studied. These are equivalent to the origin of replication in E. In yeast, which is a eukaryote, special sequences known as autonomously replicating sequences (ARS) are found on the chromosomes. The rate of replication is approximately 100 nucleotides per second, much slower than prokaryotic replication. There are multiple origins of replication on each eukaryotic chromosome humans can have up to 100,000 origins of replication across the genome. The human genome has 3 billion base pairs per haploid set of chromosomes, and 6 billion base pairs are replicated during the S phase of the cell cycle. Eukaryotes also have a number of different linear chromosomes. Eukaryotic genomes are much more complex and larger in size than prokaryotic genomes.
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