In which direction does DNA polymerase synthesize the new strand?

In which direction does DNA polymerase synthesize the new strand?

• A. From 3' to 5'
• B. From 5' to 3'
• C. In both directions
• D. From 5' to 5'

Answer: (B)

DNA polymerase can only add new nucleotides to the free 3' end of the growing strand, so the strand elongates in the 5' to 3' direction. The template is read in the opposite direction (3' to 5') to ensure the correct bases are paired. This 5' to 3' synthesis rule also explains why the lagging strand is made in short segments (Okazaki fragments), each synthesized 5' to 3' and then joined. The other options would require building in a direction that the enzyme chemistry does not support.

DNA polymerase can only add new nucleotides to the free 3' end of the growing strand, so the strand elongates in the 5' to 3' direction. The template is read in the opposite direction (3' to 5') to ensure the correct bases are paired. This 5' to 3' synthesis rule also explains why the lagging strand is made in short segments (Okazaki fragments), each synthesized 5' to 3' and then joined. The other options would require building in a direction that the enzyme chemistry does not support.