Name: pentose phosphate pathway and entner-doudoroff
Uploaded: 2025-06-12T09:33:57.000Z
Duration: 1 min 24 s
Channel: JoVE

La voie du pentose phosphate fonctionne en même temps que la glycolyse pour décomposer les pentoses et le glucose. Dans la phase oxydative, le glucose-6-phosphate est oxydé pour générer du NADPH, la forme réduite de la coenzyme NADP, un agent réducteur essentiel pour la biosynthèse des acides nucléiques, de certains acides aminés et des acides gras. La phase non oxydative génère du ribose-5-phosphate, un précurseur essentiel pour la synthèse des nucléotides et de certains acides aminés. La voie du pentose phosphate ne produit pas directement de l’ATP, mais les intermédiaires peuvent entrer dans la glycolyse lorsque les bactéries ont besoin d’ATP. La voie Entner-Doudoroff, que l’on trouve principalement dans les bactéries aérobies à Gram négatif, offre une alternative à la glycolyse, produisant une molécule de pyruvate et une molécule de glycéraldéhyde-3-phosphate. Un catabolisme supplémentaire du glycéraldéhyde-3-phosphate produit un pyruvate supplémentaire. Pour chaque molécule de glucose, l’EDP produit un ATP, un NADH et un NADPH. Bien que l’EDP produise moins d’ATP que la glycolyse, le NADPH est précieux pour les voies de biosynthèse.

autres voies glycolytiques

Other Glycolytic Pathways

La voie des pentoses phosphates (PPP) fonctionne en parall&#232;le avec la glycolyse, facilitant le m&#233;tabolisme des pentoses et du glucose. Cette voie comporte deux phases distinctes : la phase oxydative et la phase non oxydative. Bien qu&#8217;elle ne g&#233;n&#232;re pas directement d&#8217;ATP, les interm&#233;diaires form&#233;s au cours du processus peuvent &#234;tre r&#233;int&#233;gr&#233;s &#224; la glycolyse, contribuant ainsi au m&#233;tabolisme &#233;nerg&#233;tique cellulaire lorsque cela est n&#233;cessaire.
Phase oxydative : production de NADPH
La phase oxydative de la voie des pentoses phosphates est principalement responsable de la production de nicotinamide ad&#233;nine dinucl&#233;otide phosphate (NADPH), un agent r&#233;ducteur essentiel. Au cours de cette phase, le glucose-6-phosphate subit une s&#233;rie de r&#233;actions enzymatiques aboutissant &#224; la formation de ribulose-5-phosphate. Deux mol&#233;cules de NADPH sont produites pour chaque mol&#233;cule de glucose-6-phosphate oxyd&#233;e. Le NADPH joue un r&#244;le crucial dans les r&#233;actions anaboliques, notamment la biosynth&#232;se des acides nucl&#233;iques, des acides amin&#233;s et des acides gras, ainsi que dans le maintien de l&#8217;&#233;quilibre redox cellulaire par la r&#233;g&#233;n&#233;ration du glutathion r&#233;duit.
Phase non oxydative : ribose-5-phosphate et interm&#233;diaires glycolytiques
La phase non oxydative de la PPP produit du ribose-5-phosphate, un pr&#233;curseur essentiel &#224; la synth&#232;se des nucl&#233;otides et de certains acides amin&#233;s. Cette phase implique l&#8217;interconversion r&#233;versible de phosphates de sucre, permettant &#224; la voie de s&#8217;adapter aux besoins m&#233;taboliques de la cellule. Si le ribose-5-phosphate n&#8217;est pas requis pour la synth&#232;se des nucl&#233;otides, la voie redirige les interm&#233;diaires carbon&#233;s vers la glycolyse via des r&#233;actions catalys&#233;es par la transk&#233;tolase et la transaldolase, reliant ainsi la PPP au m&#233;tabolisme central du carbone.
La voie d&#8217;Entner-Doudoroff : une alternative &#224; la glycolyse
La voie d&#8217;Entner-Doudoroff (EDP) est une voie alternative de catabolisme du glucose, principalement observ&#233;e chez les bact&#233;ries a&#233;robies &#224; Gram n&#233;gatif telles que Pseudomonas et Escherichia coli. Contrairement &#224; la glycolyse, qui commence par un investissement initial en ATP, la voie EDP contourne cette &#233;tape en d&#233;gradant le glucose en une mol&#233;cule de pyruvate et une mol&#233;cule de glyc&#233;rald&#233;hyde-3-phosphate. Cette derni&#232;re est ensuite m&#233;tabolis&#233;e par la voie glycolytique, produisant une mol&#233;cule de pyruvate suppl&#233;mentaire. Ce processus g&#233;n&#232;re une mol&#233;cule d&#8217;ATP, une de NADH et une de NADPH par mol&#233;cule de glucose m&#233;tabolis&#233;e. Bien que l&#8217;EDP produise moins d&#8217;ATP que la glycolyse, le NADPH g&#233;n&#233;r&#233; est b&#233;n&#233;fique pour les r&#233;actions biosynth&#233;tiques, en particulier lorsque le pouvoir r&#233;ducteur est plus crucial que la production d&#8217;ATP.
Flexibilit&#233; m&#233;tabolique et fonction cellulaire
La voie des pentoses phosphates et la voie d&#8217;Entner-Doudoroff illustrent toutes deux la flexibilit&#233; m&#233;tabolique des cellules bact&#233;riennes. La PPP fournit des pr&#233;curseurs biosynth&#233;tiques essentiels et du pouvoir r&#233;ducteur, tandis que l&#8217;EDP offre une voie alternative pour le m&#233;tabolisme du glucose, notamment chez les organismes d&#233;pourvus de certaines enzymes glycolytiques. L&#8217;int&#233;gration de ces voies &#224; la glycolyse permet aux cellules bact&#233;riennes de s&#8217;adapter efficacement &#224; des conditions nutritionnelles vari&#233;es, en optimisant la production d&#8217;&#233;nergie et la biosynth&#232;se selon les besoins.

Autres voies glycolytiques

La voie des pentoses phosphates (PPP) fonctionne en parall&#232;le avec la glycolyse, facilitant le m&#233;tabolisme des pentoses et du glucose. Cette ...

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pentose phosphate pathway and entner-doudoroff

The pentose phosphate pathway works alongside glycolysis in cells that need both sugar breakdown and building blocks for growth. It handles pentoses, which are five-carbon sugars, and also uses glucose as a starting point. The pathway has two parts, an oxidative phase and a non-oxidative phase. It does not make ATP directly, but its products can feed back into glycolysis when the cell needs them.

The oxidative phase mainly makes NADPH, a reduced electron carrier. In this phase, glucose-6-phosphate goes through several enzyme steps and becomes ribulose-5-phosphate. Two NADPH molecules are produced from each glucose-6-phosphate that is oxidized. NADPH is important for building nucleic acids, amino acids, and fatty acids, and it also helps keep the cell in redox balance by regenerating reduced glutathione.

The non-oxidative phase makes ribose-5-phosphate, which cells use to build nucleotides. It also supports the production of certain amino acids. This phase uses reversible reactions that move sugar phosphates between forms, so the pathway can match the cell’s current needs. If ribose-5-phosphate is not needed for nucleotide synthesis, carbon intermediates are sent into glycolysis through transketolase and transaldolase reactions.

The Entner-Doudoroff pathway is another way to break down glucose. It is found mainly in aerobic gram-negative bacteria such as Pseudomonas and Escherichia coli. Unlike glycolysis, it skips the ATP investment step at the start. Glucose is split into one pyruvate and one glyceraldehyde-3-phosphate, and the glyceraldehyde-3-phosphate is then processed through glycolysis to make a second pyruvate.

This pathway makes one ATP, one NADH, and one NADPH per glucose molecule. That is less ATP than glycolysis, but the NADPH can be useful for biosynthesis. It matters most when a cell needs reducing power more than ATP. Together, the pentose phosphate pathway and the Entner-Doudoroff pathway show how bacteria can adjust metabolism to fit changing nutrient conditions and support both energy use and biosynthesis.

Pentose Phosphate Pathway and Entner-Doudoroff

pentose-phosphate-pathway-and-entner-doudoroff

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The pentose phosphate pathway works alongside glycolysis in cells that need both sugar breakdown and building blocks for growth. It handles pentoses, which are five-carbon sugars, and also uses glucose as a starting point. The pathway has two parts, an oxidative phase and a non-oxidative phase. It does not make ATP directly, but its products can feed back into glycolysis when the cell needs them. The oxidative phase mainly makes NADPH, a reduced electron carrier. In this phase,...

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key terms and concepts

Learn how the pentose phosphate pathway makes NADPH and ribose-5-phosphate, and how the Entner-Doudoroff pathway helps bacteria metabolize glucose.

Pentose Phosphate Pathway and Entner-Doudoroff | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

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Pentose Phosphate Pathway and Entner-Doudoroff

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