Metabolism is the sum of all of the chemical activities cells undergo throughout their lives. It is composed of two main subdivisions:
Catabolism is the breakdown of biological molecules. Cells require nutrients containing energy stored in the carbon-to-carbon bonds of organic compounds, as well as inorganic substances that act as key components in all metabolic activities. Catabolic reactions serve to release energy and make substances in nutrients available for use.
Anabolism (biosynthesis) is the building of new, novel organic compounds, utilizing the substances broken down by catabolic reactions. Anabolic pathways are necessary to synthesize metabolic and genetic materials, as well as those necessary for growth and reproduction.
Both types of reactions occur through a series of enzyme-mediated steps called metabolic pathways. Linked anabolic and catabolic processes are called amphibolic pathways.
The primary molecule used to store and deliver energy for all cell functions is adenosine triphosphate (ATP), a form of modified RNA nucleotide composed of the nitrogenous base adenine, the five-carbon sugar ribose and three phosphate groups, the last two of which are linked by high-energy covalent bonds.