Anabolism (from and "to throw") is the set of
metabolic pathways that construct molecules from smaller units. These reactions require
energy. One way of categorizing
metabolic processes, whether at the
cellular, organ or organism level, is as "anabolic", or as "
catabolic" which is the opposite. Anabolism is powered by catabolism, where large molecules are broken down into smaller parts and then used up in
respiration. Many anabolic processes are powered by the
hydrolysis of adenosine triphosphate (ATP).