In which direction does DNA polymerase synthesize new DNA?

In which direction does DNA polymerase synthesize new DNA?

• A. 3' to 5'
• B. 5' to 3'
• C. 5' to 3'
• D. 3' to 3'

Answer: (C)

DNA polymerase can only add new nucleotides to the 3' end of a growing DNA strand, so synthesis proceeds in the 5' to 3' direction. The enzyme catalyzes the formation of a phosphodiester bond between the 3' hydroxyl of the existing strand and the 5' phosphate of the incoming nucleotide, extending the chain in that direction. While the template strand is read in the opposite direction (3' to 5') to guide base pairing, the new strand itself is built from its own 5' end toward its 3' end. A primer with a free 3' end is required to start synthesis, and this universal directionality applies to both the leading and lagging strands (the latter being synthesized in fragments that are later joined).

DNA polymerase can only add new nucleotides to the 3' end of a growing DNA strand, so synthesis proceeds in the 5' to 3' direction. The enzyme catalyzes the formation of a phosphodiester bond between the 3' hydroxyl of the existing strand and the 5' phosphate of the incoming nucleotide, extending the chain in that direction. While the template strand is read in the opposite direction (3' to 5') to guide base pairing, the new strand itself is built from its own 5' end toward its 3' end. A primer with a free 3' end is required to start synthesis, and this universal directionality applies to both the leading and lagging strands (the latter being synthesized in fragments that are later joined).