How does duplication of DNA occur in the mitotic cycle? Explain the biological meaning of this process.

DNA doubling occurs in the synthetic phase of the interphase. Each DNA molecule is converted into two identical daughter DNA molecules. This is necessary so that during cell division each daughter cell receives its own copy of DNA. The DNA helicase enzyme breaks the hydrogen bonds between nitrogenous bases, a double DNA strand breaks into two single ones. Then the DNA polymerase enzyme completes each single chain to double according to the principle of complementarity. Each daughter DNA contains one strand of maternal DNA and one newly synthesized – this is the principle of semi-conservatism. According to the principle of antiparallelism, DNA chains lie at opposite ends to each other. DNA can be extended only by the 3′-end, therefore, in each replication fork, only one of the two chains is synthesized continuously. The second chain (lagging) grows in the 5′-direction with the help of short (100-200 nucleotides) Okazaki fragments, each of which grows in the 3′-direction, and then joins the previous chain with the help of the DNA ligase enzyme. The replication rate in eukaryotes is 50-100 nucleotides per second. Each chromosome has many replication origin points, from each of which 2 replication forks diverge; Due to this, all replication takes about an hour. Doubling DNA is called the complex process of its self-reproduction. Due to the property of DNA molecules, reproduction is possible as well as the transmission of heredity by the body to its offspring, because the complete data on the structure and functioning are encoded in the gene information of organisms. DNA – is the basis of the hereditary materials of most micro- and macroorganisms. The correct name for the process of DNA doubling is replication (reduction).

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