Why is the synthesis of polynucleotides directed from the 5' end to the 3' end?

• A. The 3' end has a free hydroxyl group that allows the addition of nucleotides, while the 5' end is blocked by a phosphate group.
• B. The synthesis is directed by the template strand, which is always read from the 5' to the 3' end.
• C. DNA and RNA polymerases can only catalyze the formation of phosphodiester bonds between the 5' phosphate of the incoming nucleotide and the 3' hydroxyl group of the growing chain.
• D. The directionality is due to the higher energy of the phosphate group at the 3' end.

Answer: (C)