In which direction does DNA polymerase read the template strand?

In which direction does DNA polymerase read the template strand?

• A. 5' to 3' direction.
• B. 3' to 5' direction.
• C. It does not have a directional preference.
• D. It reads only the leading strand.

Answer: (B)

DNA polymerase can only extend DNA by adding nucleotides to a growing strand’s 3' end, so the new strand is synthesized in the 5' to 3' direction. To place the correct bases, the enzyme must read the template in the opposite direction, which is 3' to 5'. Because the two strands are antiparallel, each template is read 3' to 5' as replication proceeds, with synthesis on the new strand occurring 5' to 3' (continuously on the leading strand and in fragments on the lagging strand). This is why the direction of reading the template is 3' to 5'.

DNA polymerase can only extend DNA by adding nucleotides to a growing strand’s 3' end, so the new strand is synthesized in the 5' to 3' direction. To place the correct bases, the enzyme must read the template in the opposite direction, which is 3' to 5'. Because the two strands are antiparallel, each template is read 3' to 5' as replication proceeds, with synthesis on the new strand occurring 5' to 3' (continuously on the leading strand and in fragments on the lagging strand). This is why the direction of reading the template is 3' to 5'.