“DNA replication en” By LadyofHats Mariana Ruiz – Own work – renamed from File: DNA replication.svg (Public Domain) via Commons WikimediaĢ. “Okazaki Fragments.” Okazaki Fragments – Biology As Poetry, Available here. It forms Okazaki fragments on the lagging strand that are ligated later by DNA ligase. Since the lagging strands run in the 3’ to 5’ direction, the DNA synthesis on the lagging strand is discontinuous. Okazaki fragments are the short DNA fragments on the lagging strand formed during DNA replication. Hence, the DNA synthesis at the lagging strand is discontinuous and the resultant DNA stretches are known as Okazaki fragments. However, the synthesis is paused when it reaches 5’ end of the RNA primer of the already-synthesized DNA stretch. Once the replication fork moves forward on the DNA double-strand, DNA polymerase can add nucleotides onto the lagging strand. Unwinding is critical in the synthesis of new DNA strands on the original strands. The replication fork is the position on the DNA double-strand where the unwinding begins. Then the synthesis of another DNA strand begins at the replication fork. However, since the lagging strand runs in the 5’ to 3’ direction, the chain growth of the newly-synthesizing DNA strand is paused when it reaches the 5’ end of the strand. Since the leading strand runs in the 3’ to 5’ direction, the enzyme can continuously add nucleotides to the growing strand on the leading strand. Generally, DNA polymerase adds nucleotides in the 5’ to 3’ direction. An Okazaki fragment is shown in figure 1.įigure 2: DNA Synthesis on Leading and Lagging Strands At the 5’ end of the Okazaki fragment, an RNA primer, which is approximately 120 nucleotides long, can be identified. In eukaryotes, Okazaki fragments are 100 to 200 nucleotides long. They form short double-stranded DNA sections that lie between 1,000 and 2,000 nucleotides in prokaryotes. Therefore, Okazaki fragments are complementary to the lagging strand, which runs in the 5’ to 3’ direction. Okazaki fragment is a short newly-synthesized DNA fragment on the lagging template strand formed during DNA replication. Key Terms: DNA Replication, Double-Stranded DNA, Lagging Strand, Leading Strand, Okazaki Fragments, Replication Fork Therefore, Okazaki fragments are formed during the synthesis of lagging template strand. However, since the double-stranded DNA is antiparallel, DNA synthesis should occur in both directions. It only synthesizes DNA in the 5’ to 3’ direction. DNA polymerase is the enzyme responsible for DNA replication. Hence, both strands should serve as a template in DNA replication. DNA replication occurs in a semi-conservative manner where one of the DNA strands in the newly synthesized double-stranded DNA is an original strand. During cell division, the complete DNA in the genome should be replicated, doubling the amount of DNA in the parent cell. Generally, DNA is a double-stranded molecule that contains two antiparallel DNA strands held together by hydrogen bonds. DNA serves as the genetic material of most organisms.
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