Name: pyruvate pathways in fermentation
Uploaded: 2025-05-22T09:05:36.000Z
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K12 Standards

Florida Department of Education

High School

Life Science

SC.912.L.18

SC.912.L.18.8

Fates of Pyruvate

Le pyruvate, le produit final de la glycolyse, peut avoir plusieurs destins métaboliques en fonction des conditions physiologiques à l’intérieur de l’organisme.
Dans des conditions aérobies, le pyruvate est converti en acétyl-coenzyme A, qui est ensuite canalisée à travers le cycle TCA et la chaîne de transport d’électrons pour produire de l’énergie sous forme d’ATP.
Mais, dans des conditions anaérobies, la chaîne de transport d’électrons ne fonctionne pas, comme on le voit chez les levures et les bactéries anaérobies. Ainsi, le pyruvate est fermenté en éthanol tout en oxydant le NADH en NAD+. Le NAD+ est ensuite recyclé en glycolyse.
Chez la plupart des vertébrés, des conditions temporaires de faible teneur en oxygène déclenchent une autre forme de fermentation du pyruvate, où il est fermenté en lactate, produisant du NAD+.
La régénération du NAD+ pendant la fermentation aide les cellules à continuer à produire de l’ATP même dans des conditions de faible teneur en oxygène via la glycolyse.
En cas d’hypoglycémie, le pyruvate peut également être reconverti en glucose 6-phosphate par un processus appelé gluconéogenèse. Le glucose 6-phosphate est ensuite converti en glucose, ce qui rétablit le taux de glucose dans le sang.

le devenir du pyruvate

Le pyruvate est le produit final de la glycolyse, où le glucose est oxydé en pyruvate, réduisant simultanément le NAD+ en NADH. Deux molécules d'ATP sont également produites par phosphorylation au niveau du substrat.

Dans les organismes aérobies, le pyruvate est métabolisé via le cycle de l'acide citrique pour produire des coenzymes réduites NADH et FADH2. Ces coenzymes sont ensuite oxydées dans la chaîne de transport d’électrons pour produire de l’ATP et, ce faisant, régénérer le NAD+ et le FAD. Comme on le voit dans certains types de cellules et organismes, la fermentation réduit le pyruvate en lactate en l'absence d'oxygène, ce qui oxyde le NADH en NAD+. La régénération du NAD+ permet à la glycolyse de continuer à produire de l'ATP par phosphorylation au niveau du substrat.

La fermentation à l'acide lactique

Pendant la fermentation lactique, le pyruvate accepte les électrons du NADH et est réduit en acide lactique. Les microbes, qui effectuent la fermentation homolactique, ne produisent que de l'acide lactique comme produit de fermentation. Les microbes, qui effectuent la fermentation hétérolactique, produisent un mélange d’acide lactique, d’éthanol et/ou d’acide acétique et de CO2. La production d'acide lactique par le microbiote normal empêche la croissance d'agents pathogènes dans certaines régions du corps, ce qui est important pour la santé du tractus gastro-intestinal.

La fermentation à l'éthanol

La fermentation éthanolique du pyruvate par la levure Saccharomyces cerevisiae est utilisée dans la production de boissons alcoolisées et fait également lever les produits panifiés grâce à la production de CO2. En dehors de l’industrie alimentaire, la fermentation éthanolique des produits végétaux est importante dans la production de biocarburants.

Plusieurs produits de fermentation sont importants commercialement en dehors de l’industrie alimentaire. Par exemple, des solvants chimiques tels que l'acétone et le butanol sont produits lors de la fermentation acétone-butanol-éthanol. Les composés pharmaceutiques organiques complexes utilisés dans les antibiotiques (par exemple la pénicilline), les vaccins et les vitamines sont produits par fermentation acide mixte.

Ce texte est adapté de <a href="https://openstax.org/books/biology-2e/pages/7-5-metabolism-without-oxygen">Openstax, Biology 2e, Section 7.5: Metabolism without oxygen</a>

Le devenir du Pyruvate

Le pyruvate est le produit final de la glycolyse, où le glucose est oxydé en pyruvate, réduisant simultanément le NAD+ en NADH. Deux molécules d’ATP sont également ...

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Introduction to Metabolism

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pyruvate pathways in fermentation

Pyruvate is a key product of glycolysis and can follow different pathways depending on oxygen availability. During glycolysis, glucose is oxidized to pyruvate, NAD+ is reduced to NADH, and two ATP are made by substrate-level phosphorylation. In aerobic organisms, pyruvate then enters the citric acid cycle, which helps produce the reduced coenzymes NADH and FADH2. These coenzymes are later oxidized in the electron transport chain to make ATP and regenerate NAD+ and FAD.

When oxygen is absent, some cells and organisms use fermentation to keep energy production going. Fermentation reduces pyruvate to lactate and oxidizes NADH back to NAD+. This regeneration of NAD+ is important because it allows glycolysis to continue making ATP by substrate-level phosphorylation.

In lactic acid fermentation, pyruvate accepts electrons from NADH and becomes lactic acid. Microbes that carry out homolactic fermentation make only lactic acid. Microbes that carry out heterolactic fermentation make a mix of lactic acid, ethanol and/or acetic acid, and CO2. Lactic acid made by normal microbiota can help prevent pathogen growth in some body regions and supports gastrointestinal tract health.

Pyruvate can also be fermented to ethanol by the yeast Saccharomyces cerevisiae. This process is used to make alcoholic beverages and helps bread rise because it releases CO2. Ethanol fermentation of plant products is also important in biofuel production. Other fermentation products have commercial value too. Acetone and butanol are made during acetone-butanol-ethanol fermentation, and complex organic compounds used in antibiotics such as penicillin, vaccines, and vitamins are produced through mixed acid fermentation.

Pyruvate Pathways in Fermentation

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fates of pyruvate

Pyruvate is a key product of glycolysis and can follow different pathways depending on oxygen availability. During glycolysis, glucose is oxidized to pyruvate, NAD+ is reduced to NADH, and two ATP are made by substrate-level phosphorylation. In aerobic organisms, pyruvate then enters the citric acid cycle, which helps produce the reduced coenzymes NADH and FADH2. These coenzymes are later oxidized in the electron transport chain to make ATP and regenerate NAD+ and FAD. When oxygen is absent,...

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Explore how pyruvate is used in aerobic respiration and fermentation, including lactic acid and ethanol fermentation, ATP production, and real-world uses.

Pyruvate Pathways in Fermentation | JoVE K12

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SC.912.L.18.7

A. All living things are composed of four basic categories of macromolecules and share the same basic needs for life.

B. Living organisms acquire the energy they need for life processes through various metabolic pathways (primarily photosynthesis and cellular respiration).

C. Chemical reactions in living things follow basic rules of chemistry and are usually regulated by enzymes.

D. The unique chemical properties of carbon and water make life on Earth possible.

Pyruvate Pathways in Fermentation

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