DNA synthesis direction?

DNA synthesis direction?

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

Answer: (A)

DNA synthesis proceeds in the 5' to 3' direction because DNA polymerases can only add nucleotides to the free 3' end of a growing strand. Each incoming nucleotide carries a 5' triphosphate, and when it is incorporated, two phosphates are released as pyrophosphate, providing the energy for bond formation. The template strand is read in the opposite direction (3' to 5'), so the new strand is built from 5' to 3'. In replication, the leading strand is synthesized continuously toward the fork, while the lagging strand is made in short 5' to 3' segments (Okazaki fragments) that are later joined. This makes 5' to 3' the universal direction of DNA synthesis.

DNA synthesis proceeds in the 5' to 3' direction because DNA polymerases can only add nucleotides to the free 3' end of a growing strand. Each incoming nucleotide carries a 5' triphosphate, and when it is incorporated, two phosphates are released as pyrophosphate, providing the energy for bond formation. The template strand is read in the opposite direction (3' to 5'), so the new strand is built from 5' to 3'. In replication, the leading strand is synthesized continuously toward the fork, while the lagging strand is made in short 5' to 3' segments (Okazaki fragments) that are later joined. This makes 5' to 3' the universal direction of DNA synthesis.