Metabolic pathways are designed to synthesize necessary cellular reagents as required for cellular and tissue function. to accomplish this, the reaction sequence

To accomplish this, the reaction sequence includes both reactions irreversible and reversible.

Irreversible reactions are the ones that include conversion of reactants to products where the products cannot convert back to the reactants. On the other hand in reversible reactions, the reactants and products are never fully consumed (constantly are reacting and being produced).