Coenzyme
Say it: koh-EN-zym
A coenzyme is a small organic molecule, often made from a vitamin, that an enzyme needs to catalyze its reaction, usually by carrying electrons or atoms.
Also: coenzymes
Definition
What is a coenzyme?
A coenzyme is a non-protein organic helper that many enzymes need in order to work. Coenzymes belong to the wider group of cofactors, which also includes metal ions such as zinc, iron and magnesium, although some textbooks keep the word cofactor for the metal ions alone. An enzyme lacking its helper is called an apoenzyme, and the complete, active form is a holoenzyme. Coenzymes bound very tightly or permanently to their enzyme are known as prosthetic groups.
Most coenzymes work as carriers. They accept electrons, hydrogen atoms or small chemical groups in one reaction and hand them on in another, and are then recycled, so a little goes a long way. NAD+ and FAD carry electrons from the breakdown of glucose and fats to the electron transport chain, coenzyme A carries two-carbon acetyl groups into the citric acid cycle, and biotin carries carbon dioxide. ATP is sometimes counted among them because it transfers phosphate groups.
Many coenzymes are made from B vitamins: NAD+ from niacin, FAD from riboflavin, coenzyme A from pantothenic acid and thiamine pyrophosphate from thiamine. That is why vitamin deficiencies disrupt metabolism. Without enough thiamine, for example, enzymes such as pyruvate dehydrogenase falter, and the deficiency disease beriberi develops.
Word parts
Where does the word “coenzyme” come from?
- co-
- together, withLatin co-, com-
- en-
- inGreek en
- -zyme
- leaven, yeastGreek zyme
Practice it
Where you'll meet it
Related
Terms that go with it
- EnzymeAn enzyme is a biological catalyst, usually a protein, that speeds up a specific chemical reaction without being used up in the process.
- VitaminA vitamin is an organic compound that the body needs in small amounts for normal metabolism, growth and health, and must mostly obtain from food.
- ATPATP (adenosine triphosphate) is the molecule cells use as their main short-term energy carrier, releasing energy when a phosphate group is removed.
- Active siteThe active site is the pocket or groove on an enzyme where the substrate binds and the chemical reaction is catalyzed.
- MicronutrientA micronutrient is a vitamin or mineral that the body needs only in tiny amounts but cannot do without, such as iron, iodine, vitamin A or folate.
- MetabolismMetabolism is the full set of chemical reactions in a cell or organism, both those that break molecules down for energy and those that build them up.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Biology 2e, 6.5 Enzymes
- OpenStax Anatomy and Physiology 2e, 24.2 Carbohydrate Metabolism
- NCBI MeSH: Coenzymes
Last updated
Spotted a mistake? Tell us and we'll correct it.
Practice Biochemistry
Free biochemistry quizzes, with an explanation for every answer.
See the Quizzes