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DNA160-page10 - DNA Structure and Replication 10 D NA...

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DNA: Structure and Replication - 10 DNA Polymerase and the Single Chain Template DNA polymerase's inability to add nucleotides to a single chain is solved by starting replication with a RNA primer activated by an enzyme called primase. Primase catalyzes a short RNA molecule or primer that is used to start the synthesis of DNA. Once the DNA strand has been "primed" by primase adding the RNA primer, DNA polymerase can go to work adding nucleotides to the available 3' carbon of the growing molecule. (This is sometimes called the free sugar end of the DNA molecule. The opposite end 5' carbon of the nucleotide's sugar that bonds to the phosphate is called the free phosphate end.) DNA polymerase will also eventually replace the RNA nucleotides of the primer with DNA nucleotides. DNA and the Anti-parallel Template Strands For DNA's second limitation, DNA polymerase can only attach a nucleotide to the exposed -OH group on the 3' end of the sugar on the template. DNA is always synthesized in the 5' ±
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