A metabolic pathway is a series of linked chemical reactions that occur within a cell. These reactions involve metabolites, which are the reactants, products, and intermediates of an enzymatic reaction. There are two types of metabolic pathways: anabolic pathways, which synthesize molecules with the utilization of energy, and catabolic pathways, which break down complex molecules and release energy in the process. The flux of metabolites through a pathway is regulated depending on the needs of the cell and the availability of the substrate, and the end product of a pathway may be used immediately, initiate another metabolic pathway, or be stored for later use.
Metabolic pathways are required for the maintenance of homeostasis within an organism. The metabolism of a cell consists of an elaborate network of interconnected pathways that enable the synthesis and breakdown of molecules. An example of an anabolic pathway is gluconeogenesis, which occurs in the liver and sometimes in the kidney to maintain proper glucose concentration in the blood and supply the brain and muscle tissues with an adequate amount of glucose.
Metabolic pathways happen in specific locations in the cell. For example, glycolysis, fatty acid synthesis, and glycogen synthesis happen in the cytoplasm, along with some steps of amino acid breakdown. Several metabolic pathways are in specific locations inside mitochondria, which are organelles surrounded by two layers of membrane. The matrix, which is inside of both membranes, is home to beta oxidation, the citric acid cycle, and some steps of amino acid breakdown. The components of oxidative phosphorylation—the electron transport chain and ATP synthase—are embedded within the inner mitochondrial membrane.
Metabolic pathways are essential for the body to produce energy. The body uses different metabolic pathways, or types of chemical reactions, to produce the right kind of energy to fuel different activities. The body has three different metabolic pathways: the phosphagen system (ATP-PC system) for immediate energy, the glycolytic system for short-term energy, and the oxidative system for long-term energy. It is possible to train the body to use each metabolic system, a process called metabolic conditioning.
