5 - DNA Replication, Repair, and Recombination Review...

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DNA Replication, Repair, and Recombination Review cellular mechanisms of DNA replication and repair. DNA recombination and the movement of transposable elements Viruses
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All organisms must duplicate their DNA with extraordinary accuracy before each cell division. DNA replication occurs in the S phase of the cell cycle.
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Each strand of DNA double helix contains a sequence of nucleotides that is complementary to the nucleotide sequence of the partner strand. This means every strand can serve as a template for the synthesis of a new strand.
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This is the basis for semiconservative nomenclature for DNA replication. This copying (of the entire genome) can be carried out in an animal cell in about 8 hours and enables the cell to pass its genetic information on in a reliable fashion.
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DNA synthesis Involves initiator proteins that bind to the DNA. The initiator proteins start at a replication origin . These proteins associate with an additional complex called a helicase. The nucleotides A and T are held together by fewer hydrogen bonds than the G-C pairning. It appears that replication origins are in regions rich in A-T stretches. Bacterial cell DNA may have a single replication origin, while the DNA in human cells may have many.
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06_09_Replic.forks.jpg One can observe replication with an electron microscope. The opened strand areas – replication forks – are visible above. Two replication forks are formed starting at a replication origin, and they move away from the origin in opposite directions. This allows DNA replication to be bidirectional.
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Replication moves very rapidly from 100 nucleotide pairs per second (human cell) to 1000 nucleotide pairs per second (bacterial cell). The slower rate in human (eukaryotic cells) may be due to the
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5 - DNA Replication, Repair, and Recombination Review...

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