![]() ![]() Semiconservative model of DNA replicationĭeoxyribonucleic acid, abbreviated DNA, is a macro molecule containing genetic information which characterizes each organism this information is used in the development and maintenance of the organism. Mismatch repair and nucleotide excision repair diagram ![]() ![]() Title: Biology – 9.2 DNA Replication – DNA Replication in Eukaryotes DNA Repair OpenStax CNX. Thus, the ends of the chromosomes are replicated. Once the lagging strand template is sufficiently elongated, DNA polymerase can now add nucleotides that are complementary to the ends of the chromosomes. Complementary bases to the RNA template are added on the end of the DNA strand. The telomerase attaches to the end of the chromosome. The discovery of the enzyme telomerase helped in the understanding of how chromosome ends are maintained. For example, a six base-pair sequence, TTAGGG, is repeated 100 to 1000 times in humans. As a consequence, it is telomeres that are shortened with each round of DNA replication instead of genes. The ends of the linear chromosomes are known as telomeres, which have repetitive sequences that do not code for a particular gene. This presents a problem for the cell because the ends remain unpaired, and over time these ends get progressively shorter as cells continue to divide. In the leading strand, synthesis continues until the end of the chromosome is reached however, on the lagging strand there is no place for a primer to be made for the DNA fragment to be copied at the end of the chromosome. As you have learned, the DNA polymerase enzyme can add nucleotides in only one direction. As synthesis proceeds, an enzyme removes the RNA primer, which is then replaced with DNA nucleotides, and the gaps between fragments are sealed by an enzyme called DNA ligase.īecause eukaryotic chromosomes are linear, DNA replication comes to the end of a line in eukaryotic chromosomes. The strand with the Okazaki fragments is known as the lagging strand. The Okazaki fragments each require a primer made of RNA to start the synthesis. ![]() Because DNA polymerase can only synthesize DNA in a 5′ to 3′ direction, the other new strand is put together in short pieces called Okazaki fragments. This continuously synthesized strand is known as the leading strand. One strand, which is complementary to the parental DNA strand, is synthesized continuously toward the replication fork so the polymerase can add nucleotides in this direction. This primer is removed later, and the nucleotides are replaced with DNA nucleotides. Because DNA polymerase can only add new nucleotides at the end of a backbone, a primer sequence, which provides this starting point, is added with complementary RNA nucleotides. During elongation, an enzyme called DNA polymerase adds DNA nucleotides to the 3′ end of the template. ![]()
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