What is the direction of the new antiparallel strand synthesized by DNA polymerase?

What is the direction of the new antiparallel strand synthesized by DNA polymerase?

• A. 5' → 3'
• B. 3' → 5'
• C. 5' → 3' on the template
• D. 3' → 5' on the template

Answer: (B)

The main idea is that DNA polymerase can only add nucleotides to the 3' end of a growing strand, so the new strand is synthesized in the 5' to 3' direction. Because the two strands of DNA run antiparallel to each other, the template must be read in the opposite direction to keep base pairing correct. That means the polymerase moves along the template from the 3' end toward the 5' end (reading the template 3'→5'), while the new strand extends from 5' to 3'. So the direction described for the reading of the template is 3'→5'.

The main idea is that DNA polymerase can only add nucleotides to the 3' end of a growing strand, so the new strand is synthesized in the 5' to 3' direction. Because the two strands of DNA run antiparallel to each other, the template must be read in the opposite direction to keep base pairing correct. That means the polymerase moves along the template from the 3' end toward the 5' end (reading the template 3'→5'), while the new strand extends from 5' to 3'. So the direction described for the reading of the template is 3'→5'.