What is the process by which nucleic acid grows?

Nucleic acid synthesis occurs through the process of adding nucleotides to a growing chain, and this addition specifically happens at the 3' end of the molecule. The growth of nucleic acid occurs when a nucleotide is added through the formation of a phosphodiester bond between the 3' hydroxyl group of the last nucleotide already in the chain and the 5' phosphate group of the incoming nucleotide.

The correct answer highlights the importance of the 5' phosphate group in this process. When a nucleotide triphosphate is incorporated into the growing nucleic acid strand, the terminal 3' hydroxyl group of the existing chain attacks the 5' phosphate group of the incoming nucleotide. This reaction results in the release of pyrophosphate (two phosphate groups) and the formation of a new bond, effectively elongating the nucleic acid chain.

Understanding this specific mechanism is crucial, as it emphasizes how the energetic properties of the phosphate groups drive the synthesis. The other options do not describe the actual process of nucleic acid growth accurately. For instance, while the 3' hydroxyl group is involved in the reaction, it is the 5' phosphate group that is critical for providing the linkage that facilitates growth.