During DNA replication, the double-stranded DNA unwinds and separates into two single strands. This process is facilitated by enzymes known as helicases, which break the hydrogen bonds between the base pairs, resulting in the formation of a replication fork. Each single strand serves as a template for the synthesis of a new complementary strand.
Key steps in DNA replication include:
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Unwinding the DNA: Helicases unwind the double helix, separating the two strands.
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Stabilization of single strands: Single-strand binding proteins (SSBs) bind to the separated strands to prevent them from re-annealing or forming secondary structures.
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Priming the strands: The enzyme primase synthesizes short RNA primers on each template strand. These primers provide a starting point for DNA synthesis because DNA polymerases require a primer with a free 3' hydroxyl (OH) group.
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DNA synthesis: DNA polymerase extends the RNA primers by adding complementary nucleotides to the growing DNA strand, synthesizing new DNA in a 5’ to 3’ direction. The leading strand is synthesized continuously, while the lagging strand is synthesized in short fragments known as Okazaki fragments.
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Removal of RNA primers: The RNA primers are removed, and the gaps are filled with DNA nucleotides.
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Ligation: The enzyme DNA ligase seals the gaps between the Okazaki fragments on the lagging strand, creating a continuous DNA strand.
At the end of replication, two identical double-stranded DNA molecules are produced, each containing one original (template) strand and one newly synthesized strand, a process known as semiconservative replication.
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