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

La via del pentoso fosfato opera contemporaneamente alla glicolisi per abbattere i pentosi e il glucosio. Nella fase ossidativa, il glucosio-6-fosfato viene ossidato per generare NADPH, la forma ridotta del coenzima NADP, un agente riducente essenziale per la biosintesi degli acidi nucleici, di alcuni amminoacidi e degli acidi grassi. La fase non ossidativa genera ribosio-5-fosfato, un precursore essenziale per la sintesi dei nucleotidi e di alcuni amminoacidi. La via del pentoso fosfato non produce direttamente ATP, ma gli intermedi possono entrare nella glicolisi quando i batteri richiedono ATP. La via di Entner-Doudoroff, che si trova principalmente nei batteri gram-negativi aerobi, fornisce un'alternativa alla glicolisi, producendo una molecola di piruvato e gliceraldeide-3-fosfato. Un ulteriore catabolismo della gliceraldeide-3-fosfato produce un ulteriore piruvato. Per ogni molecola di glucosio, l'EDP produce un ATP, un NADH e un NADPH. Sebbene l'EDP produca meno ATP rispetto alla glicolisi, il NADPH è prezioso per le vie biosintetiche.

altre vie glicolitiche

Other Glycolytic Pathways

La via del pentoso fosfato (PPP) opera in parallelo con la glicolisi, facilitando il metabolismo sia dei pentosi che del glucosio. Questa via &#232; suddivisa in due fasi distinte: una fase ossidativa e una non ossidativa. Sebbene non generi ATP direttamente, gli intermedi prodotti durante il processo possono confluire nella glicolisi, contribuendo al metabolismo energetico cellulare quando necessario.
Fase ossidativa: produzione di NADPH
La fase ossidativa della via del pentoso fosfato &#232; la principale responsabile della generazione di nicotinammide adenina dinucleotide fosfato (NADPH), un agente riducente essenziale. In questa fase, il glucosio-6-fosfato subisce una serie di reazioni enzimatiche che portano alla formazione di ribulosio-5-fosfato. Durante questa conversione, vengono prodotte due molecole di NADPH per ogni molecola di glucosio-6-fosfato ossidata. Il NADPH svolge un ruolo fondamentale nelle reazioni anaboliche, inclusa la biosintesi di acidi nucleici, aminoacidi e acidi grassi, oltre a mantenere l&#8217;equilibrio redox cellulare rigenerando il glutatione ridotto.
Fase non ossidativa: ribosio-5-Fosfato e intermedi glicolitici
La fase non ossidativa della PPP genera ribosio-5-fosfato, un precursore per la sintesi di nucleotidi e di alcuni aminoacidi. Questa fase implica l&#8217;interconversione reversibile dei fosfati degli zuccheri, permettendo alla via di adattarsi alle esigenze metaboliche della cellula. Se il ribosio-5-fosfato non &#232; richiesto per la sintesi nucleotidica, la via reindirizza gli intermedi del carbonio nella glicolisi tramite reazioni catalizzate da transchetolasi e transaldolasi, collegando la PPP al metabolismo centrale del carbonio.
La via di Entner-Doudoroff: un&#8217;alternativa alla glicolisi
La via di Entner-Doudoroff (EDP) &#232; una via alternativa di catabolismo del glucosio, presente principalmente nei batteri Gram-negativi aerobi come lo Pseudomonas e l&#8217;Escherichia coli. A differenza della glicolisi, che inizia con l&#8217;investimento preparatorio di ATP, l&#8217;EDP aggira questo passaggio, degradando il glucosio in una molecola di piruvato e una di gliceraldeide-3-fosfato. Quest&#8217;ultima subisce un ulteriore catabolismo tramite la via glicolitica, producendo un&#8217;altra molecola di piruvato. Questo processo produce una molecola di ATP, una di NADH e una di NADPH per ogni molecola di glucosio metabolizzata. Sebbene l&#8217;EDP generi meno ATP rispetto alla glicolisi, il NADPH prodotto &#232; vantaggioso per le reazioni biosintetiche, in particolare in condizioni in cui il potere riducente &#232; pi&#249; critico della generazione di ATP.
Flessibilit&#224; metabolica e funzione cellulare
Sia la via del pentoso fosfato che quella di Entner-Doudoroff illustrano la versatilit&#224; metabolica delle cellule batteriche. La PPP fornisce precursori biosintetici essenziali e potere riducente, mentre l&#8217;EDP rappresenta una via alternativa per il metabolismo del glucosio, particolarmente utile negli organismi che non dispongono di alcuni enzimi glicolitici. L&#8217;integrazione di queste vie con la glicolisi garantisce che le cellule batteriche possano adattarsi in modo efficiente a condizioni nutrizionali variabili, ottimizzando la produzione di energia e la biosintesi secondo necessit&#224;.

Altre vie glicolitiche

La via del pentoso fosfato (PPP) opera in parallelo con la glicolisi, facilitando il metabolismo sia dei pentosi che del glucosio. Questa via &#232; ...

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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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