Which direction does DNA polymerase synthesize new DNA strands?

Which direction does DNA polymerase synthesize new DNA strands?

• A. 3' to 5'.
• B. It synthesizes in both directions.
• C. It does not synthesize DNA.
• D. 5' to 3'.

Answer: (D)

DNA polymerase builds new DNA by adding nucleotides to the 3' end of a growing strand, so synthesis occurs in the 5' to 3' direction. Each incoming nucleotide forms a phosphodiester bond with the existing strand at its 3' hydroxyl group, extending the chain from the 5' end toward the 3' end. The enzyme reads the template strand in the opposite direction, 3' to 5', so the new strand runs 5' to 3'. On the leading strand this is a continuous process, while on the lagging strand it happens in short segments (Okazaki fragments), but each fragment is still synthesized 5' to 3'. This directional requirement is fundamental to how DNA replication is organized and why synthesis cannot proceed 3' to 5'.

DNA polymerase builds new DNA by adding nucleotides to the 3' end of a growing strand, so synthesis occurs in the 5' to 3' direction. Each incoming nucleotide forms a phosphodiester bond with the existing strand at its 3' hydroxyl group, extending the chain from the 5' end toward the 3' end. The enzyme reads the template strand in the opposite direction, 3' to 5', so the new strand runs 5' to 3'. On the leading strand this is a continuous process, while on the lagging strand it happens in short segments (Okazaki fragments), but each fragment is still synthesized 5' to 3'. This directional requirement is fundamental to how DNA replication is organized and why synthesis cannot proceed 3' to 5'.