Anabolism (/əˈnæbəlɪzəm/) is the set of metabolic pathways that construct macromolecules like DNA or RNA from smaller units.[1][2] These reactions require energy, known also as an endergonic process.[3] Anabolism is the building-up aspect of metabolism, whereas catabolism is the breaking-down aspect. Anabolism is usually synonymous with biosynthesis.