Fermentation
Biochemistry · Microbiology · Food Nutrition
Say it: fur-men-TAY-shun
Fermentation is a way cells get energy from sugar without oxygen, passing electrons to an organic molecule so that glycolysis can keep going.
Definition
What is fermentation?
Fermentation is a way of getting energy from sugar without oxygen and without an electron transport chain. During glycolysis, glucose is split into two molecules of pyruvate, making a little ATP and turning the carrier NAD+ into NADH. Fermentation then hands the electrons from NADH to an organic molecule, usually pyruvate or something made from it. This regenerates NAD+, which glycolysis needs in order to keep running.
The two best-known types differ in their end products. In lactic acid fermentation, the enzyme lactate dehydrogenase converts pyruvate to lactate; this happens in some bacteria, in red blood cells, which have no mitochondria, and in muscle that is short of oxygen. In alcohol fermentation, yeast first removes carbon dioxide from pyruvate to make acetaldehyde and then reduces it to ethanol. Either way, the cell gains only the two ATP from glycolysis for each glucose, far less than aerobic respiration yields.
Fermentation is behind yogurt, cheese, sauerkraut, bread, beer and wine. In the microbiology lab, testing which sugars a bacterium can ferment, and whether it makes gas, helps to identify it.
Word parts
Where does the word “fermentation” come from?
- ferment-
- leaven; linked to the idea of boiling or bubblingLatin fermentum, from fervere 'to boil'
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Related
Terms that go with it
- GlycolysisGlycolysis is the ten-step metabolic pathway that splits one glucose molecule into two pyruvate molecules, giving a net gain of two ATP.
- YeastA yeast is a single-celled fungus that usually reproduces by budding; baker's yeast ferments sugar into alcohol and carbon dioxide.
- ATPATP (adenosine triphosphate) is the molecule cells use as their main short-term energy carrier, releasing energy when a phosphate group is removed.
- 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.
- BacteriumA bacterium is a single-celled prokaryote with no nucleus, found in almost every habitat on Earth, including in and on the human body.
- Electron transport chainThe electron transport chain is a series of membrane proteins that pass electrons to oxygen and use the energy released to pump protons.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Biology 2e, 7.5 Metabolism without Oxygen
- LibreTexts, UC Davis BIS 2A Introductory Biology, 9.3 Fermentation and Regeneration of NAD+
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