On a molecular level, metabolism is made up of the biological processes that build or break molecules; on an organismal level, metabolism is all of the chemical reactions within an organism that provide cells with the capacity to acquire energy and use that energy to carry out different functions. Metabolism includes two main components: catabolism and anabolism. First, cells obtain energy by breaking down food molecules in a process called catabolism, which is a sequence of chemical reactions that breaks down or decomposes molecules into smaller units while generating energy. The energy that is released comes from the carbohydrates, proteins, and fats that are found in food. These molecules all contain chemical potential energy, which is the energy released during a chemical reaction. Carbohydrates, proteins, and fat molecules are the first reactants in the initial steps of metabolism.
A reactant's chemical potential energy is released when the molecular bonds are broken by the cell in a chemical reaction. When molecules are broken down, the potential energy stored in their chemical bonds is released and can be used by the body to generate usable cellular energy. Anabolism, also called biosynthesis, is a sequence of chemical reactions that constructs or synthesizes molecules from smaller units—the reverse of catabolism. Anabolic reactions use energy obtained from catabolism to assemble the proteins, DNA, and RNA that can be used to build new cells. These molecules are the final products of metabolism reactions.Organisms are divided into two groups depending on how they obtain energy. An autotroph is an organism that can make its own food—for example, plants create glucose through photosynthesis. Organisms such as humans that need to ingest food are called heterotrophs. A heterotroph is an organism that obtains energy and carbon from consuming other organisms. Ultimately, heterotrophs get their food from autotrophs.
Energy in Chemical Reactions
The use and production of energy is the driving force for all chemical reactions, including those that make up metabolism.
Free energy, often referred to as Gibbs free energy (G), is the capacity of a system to do work, or the total potential energy of a system.The change in free energy that occurs during a chemical reaction is called is equal to the free energy of the products minus the free energy of the reactants, or