Set of all chemical reactions within an organism are called metabolism. There are two main types of metabolic reactions:
1. Anabolic reactions (anabolism) are reactions of synthesis or building up of the molecules. Smaller or basic units are used as precursors for the formation of the macromolecules with the help of enzymes and cofactors (monosaccharides are basic units for sugars, free fatty acids for lipids, amino acids for proteins and nucleotides for nucleic acids). Anabolic reactions require energy, which means that are endergonic process and energy is powered by catabolic reactions.
2. Catabolic reactions (catabolism) are reactions of molecule breakage-macromolecules are broken down to basic units (monomers) and energy is released. Formed monomers are used for the synthesis of new molecules or are released as waste.