4.4 Fermentation - Concepts of Biology

Vocabulary terms covering the concepts of fermentation, anaerobic respiration, and metabolic pathways in various organisms based on OpenStax Biology.

Fermentation

Processes that use an organic molecule to regenerate $NAD^+$ from $NADH$ following glycolysis when aerobic respiration does not occur.

Anaerobic Cellular Respiration

A process where the electron transport chain (ETC) uses an inorganic molecule other than oxygen ($O_2$) as a final electron acceptor to regenerate $NAD^+$.

Lactic Acid Fermentation

The fermentation method used by animals and some bacteria (like those in yogurt) where pyruvic acid and $NADH$ react to produce lactic acid and $NAD^+$.

Lactate Dehydrogenase

The enzyme that catalyzes the chemical reaction: $\text{Pyruvic acid} + NADH \rightleftharpoons \text{lactic acid} + NAD^+$.

Tremetol

A metabolic poison found in white snake root plant that prevents the metabolism of lactate; it can be concentrated in cow milk and cause illness in humans.

Alcohol Fermentation

A fermentation process that produces ethanol; it involves the removal of a carboxyl group from pyruvic acid to release $CO_2$ and the subsequent reduction of acetaldehyde by $NADH$.

Acetaldehyde

The molecule produced in alcohol fermentation after a carboxyl group is removed from pyruvic acid; it acts as the electron acceptor to become ethanol.

12 Percent

The maximum natural level of alcohol in wine because ethanol concentrations above this threshold are toxic to yeast.

Methanogens

A group of Archaea that reduce carbon dioxide ($CO_2$) to methane ($CH_4$) to oxidize $NADH$.

Sulfate-reducing Bacteria

Anaerobic microorganisms that reduce sulfate to hydrogen sulfide ($H_2S$) to regenerate $NAD^+$ from $NADH$.

Facultatively Anaerobic

Organisms that can switch between aerobic respiration and fermentation depending on the availability of oxygen.

Obligate Anaerobes

Microorganisms, such as Clostridia bacteria, that live and grow only in the absence of molecular oxygen; oxygen is a poison to them.

Gas Production in Fermentation

A byproduct used in laboratory identification of bacteria; most forms of fermentation produce gas, though lactic acid fermentation is a notable exception.