3.21 : ATP and Macromolecule Synthesis

Macromolecules such as proteins, polynucleotides, carbohydrates, and lipids are polymers of amino acids, nucleotides, monosaccharides, and fatty acids.

Since the synthesis of these macromolecules is energetically unfavorable, the energy released by ATP hydrolysis, a favorable exergonic process, is used to power these reactions.

For example, during polynucleotide chain synthesis, the terminal phosphates from two ATP molecules are released by hydrolysis. These phosphates are then transferred to nucleoside monophosphate, converting it into a high-energy intermediate called nucleoside triphosphate.

This intermediate attaches to the growing end of the polynucleotide chain by releasing pyrophosphate.

Synthesis of polymers can be oriented in two ways. In the case of lipids and proteins, synthesis occurs by head polymerization, where the reactive bond required for the condensation reaction is carried to the end of the growing polymer. Each monomer brings the reactive bond, required for the addition of the following monomer.

In tail polymerization, as seen in the synthesis of polynucleotides and carbohydrates, the reactive bond is carried by the incoming monomer, and is used immediately for its own addition.