Pyruvic acid is an organic acid found in most biological systems. It's a colorless liquid that's represented chemically as CH3COCO2H. When pyruvic acid loses a hydrogen atom it acquires a negative charge and is called pyruvate. Pyruvate is essential to many metabolic pathways required by living organisms and is represented chemically as C3H3O3.
Pyruvate is used in metabolic reactions to provide energy to an organism. Glucose — more commonly known as sugar — can be broken down in a process called glycolysis which results in the creation of pyruvate. The pyruvate can then be converted into acetyl-coenzyme A, which is necessary to start a series of reactions known as the Krebs cycle, also known as the citric acid cycle. In the Krebs cycle, oxygen is used to convert carbohydrates, fats, and proteins into carbon dioxide and water, generating energy in the process.
In a separate process, pyruvate can be converted into a compound called oxaloacetate, which is also a necessary component of the Krebs cycle. Oxaloacetate is an intermediary in gluconeogenesis, a process where the body is able to make glucose during times of extreme stress. This usually occurs during periods of starvation or intense exercise.
In the absence of oxygen, pyruvate can be broken down in humans and animals to create lactate. The conversion of pyruvate to lactate usually only occurs during intense activity, when the demand for energy is very high. When the same reaction occurs in plants or bacteria, the end product is ethanol, the central ingredient in all alcoholic beverages.
Essentially, pyruvate is required for many metabolic reactions that serve many different purposes biologically. Although it is formed from glucose, pyruvate can be converted into energy via the Krebs cycle, to carbohydrates for the storage of energy by gluconeogenesis, to protein in the form of the amino acid alanine, and to ethanol in anaerobic reactions. Interestingly, because pyruvic acid is so simple chemically and essential to many reactions necessary for sustaining life, some people think that it was one of the first organic compounds and a catalyst for origins of life on Earth.