In which direction is the new DNA strand synthesized?

In which direction is the new DNA strand synthesized?

• A. 3' to 5'
• B. 5' to 3'
• C. Both directions
• D. None of the above

Answer: (B)

DNA synthesis always proceeds in the 5' to 3' direction because DNA polymerase adds new nucleotides to the 3' end of the growing strand, forming a bond between the 3' hydroxyl group and the incoming nucleotide's phosphate. The template strand is read in the 3' to 5' direction so the bases pair correctly. This means the new strand must extend from its own 5' end toward its 3' end. On the leading strand, synthesis is continuous toward the fork; on the lagging strand, synthesis occurs in short 5' to 3' fragments that are later joined. So the direction of new DNA synthesis is 5' to 3'.

DNA synthesis always proceeds in the 5' to 3' direction because DNA polymerase adds new nucleotides to the 3' end of the growing strand, forming a bond between the 3' hydroxyl group and the incoming nucleotide's phosphate. The template strand is read in the 3' to 5' direction so the bases pair correctly. This means the new strand must extend from its own 5' end toward its 3' end. On the leading strand, synthesis is continuous toward the fork; on the lagging strand, synthesis occurs in short 5' to 3' fragments that are later joined. So the direction of new DNA synthesis is 5' to 3'.