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

The pentose phosphate pathway operates simultaneously with glycolysis to break down pentoses and glucose.In the oxidative phase, glucose-6-phosphate is oxidized to generate NADPH, the reduced form of coenzyme NADP, an essential reducing agent for the biosynthesis of nucleic acids, certain amino acids, and fatty acids.The non-oxidative phase generates ribose-5-phosphate, an essential precursor for nucleotide synthesis and certain amino acids.The pentose phosphate pathway does not directly produce ATP, but the intermediates can enter glycolysis when the bacteria require ATP.The Entner-Doudoroff pathway, primarily found in aerobic gram-negative bacteria, provides an alternative to glycolysis, producing one molecule each of pyruvate and glyceraldehyde-3-phosphate.Further catabolism of glyceraldehyde-3-phosphate yields an additional pyruvate.For each glucose molecule, the EDP produces one ATP, one NADH, and one NADPH.Though EDP produces less ATP than glycolysis, the NADPH is valuable for biosynthetic pathways.

other glycolytic pathways

Other Glycolytic Pathways

The pentose phosphate pathway (PPP) operates in parallel with glycolysis, facilitating the metabolism of both pentoses and glucose. This pathway consists of two distinct phases: the oxidative and non-oxidative phases. While it does not directly generate ATP, the intermediates formed during the process can integrate into glycolysis, contributing to cellular energy metabolism when required.Oxidative Phase: NADPH ProductionThe oxidative phase of the pentose phosphate pathway is primarily responsible for the generation of nicotinamide adenine dinucleotide phosphate (NADPH), an essential reducing agent. In this phase, glucose-6-phosphate undergoes a series of enzymatic reactions, culminating in the production of ribulose-5-phosphate. During this conversion, two molecules of NADPH are produced per molecule of glucose-6-phosphate oxidized. NADPH plays a crucial role in anabolic reactions, including the biosynthesis of nucleic acids, amino acids, and fatty acids, as well as in maintaining cellular redox balance by regenerating reduced glutathione.Non-Oxidative Phase: Ribose-5-Phosphate and Glycolytic IntermediatesThe non-oxidative phase of the PPP generates ribose-5-phosphate, a precursor for nucleotide synthesis and certain amino acids. This phase involves the reversible interconversion of sugar phosphates, allowing the pathway to adapt to the cell's metabolic needs. If ribose-5-phosphate is not required for nucleotide synthesis, the pathway redirects carbon intermediates into glycolysis through transketolase and transaldolase reactions, linking the PPP to central carbon metabolism.The Entner-Doudoroff Pathway: An Alternative to GlycolysisThe Entner-Doudoroff pathway (EDP) is an alternative glucose catabolism pathway, primarily found in aerobic gram-negative bacteria such as Pseudomonas and Escherichia coli. Unlike glycolysis, which begins with the preparatory investment of ATP, the EDP bypasses this step, breaking glucose into one molecule each of pyruvate and glyceraldehyde-3-phosphate. The latter undergoes further catabolism via the glycolytic pathway, producing an additional pyruvate molecule. This process yields one ATP, one NADH, and one NADPH per molecule of glucose metabolized. Although the EDP generates less ATP compared to glycolysis, the NADPH produced is beneficial for biosynthetic reactions, particularly under conditions where reducing power is more critical than ATP generation.Metabolic Flexibility and Cellular FunctionBoth the pentose phosphate pathway and the Entner-Doudoroff pathway illustrate the metabolic versatility of bacterial cells. The PPP provides essential biosynthetic precursors and reducing power, while the EDP offers an alternative route for glucose metabolism, particularly in organisms that lack certain glycolytic enzymes. The integration of these pathways with glycolysis ensures that bacterial cells can efficiently adapt to varying nutrient conditions, optimizing energy production and biosynthesis as needed.

The pentose phosphate pathway (PPP) operates in parallel with glycolysis, facilitating the metabolism of both pentoses and glucose. This pathway consists ...

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JoVE Core

Microbiology

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Microbial Metabolism

KEY TERMS AND CONCEPTS

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.

microbiology

Pentose Phosphate Pathway and Entner-Doudoroff

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