3' and 5' ends significance?

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3' and 5' ends significance?

The key idea is that DNA synthesis happens in the 5' to 3' direction, because nucleotides are added to the free 3' hydroxyl group of the growing strand. Each incoming nucleotide comes as a dNTP and forms a phosphodiester bond at the 3' end, releasing pyrophosphate. Therefore, new nucleotides can only be added to the 3' end, so the 5' end is considered upstream and the 3' end downstream as the chain elongates. That’s why the statement about adding to the 3' end is correct. The other ends aren’t extended because there’s no 3' hydroxyl available at the 5' end to start a new bond, and synthesis cannot proceed in both directions simultaneously; polymerases can’t add to the 5' end or to both ends equally.

The key idea is that DNA synthesis happens in the 5' to 3' direction, because nucleotides are added to the free 3' hydroxyl group of the growing strand. Each incoming nucleotide comes as a dNTP and forms a phosphodiester bond at the 3' end, releasing pyrophosphate. Therefore, new nucleotides can only be added to the 3' end, so the 5' end is considered upstream and the 3' end downstream as the chain elongates.

That’s why the statement about adding to the 3' end is correct. The other ends aren’t extended because there’s no 3' hydroxyl available at the 5' end to start a new bond, and synthesis cannot proceed in both directions simultaneously; polymerases can’t add to the 5' end or to both ends equally.

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