Entner-Doudoroff Pathway - Online Tutor, Practice Problems & Exam Prep

The Entner-Doudoroff pathway (EDP) is an alternative glycolytic pathway utilized by some bacteria, distinct from eukaryotic glycolysis. It features a single ATP investment, yielding one G3P molecule, which leads to the production of one NADH and one net ATP during the energy harvest phase. A key product of the EDP is NADPH, crucial for biosynthetic reactions, unlike the traditional glycolysis that produces no NADPH. Ultimately, both pathways generate two pyruvate molecules, but the EDP's efficiency is halved in terms of NADH and ATP production.

Entner-Doudoroff Pathway

In this video, we're going to begin our lesson on the Entner-Doudoroff pathway, which is a pathway used by some bacteria but is not used by eukaryotes. First, we need to recall that the normal glycolysis pathway that we covered in our previous lesson videos has 2 phases. The first phase of glycolysis is the energy investment phase, and the second phase is the energy harvest phase. Some bacteria, again not eukaryotes, can use an alternative pathway for the glycolysis energy investment phase. This alternative pathway to the energy investment phase is going to be called the Entner-Doudoroff pathway, commonly abbreviated as EDP. The Entner-Doudoroff pathway is an alternative to the energy investment phase. After the Entner-Doudoroff Pathway is complete, it can still transition into the energy harvest phase. The Entner-Doudoroff pathway is defined as an alternative glycolysis pathway, specifically an alternative to the energy investment phase, which will produce several molecules, including a very important molecule called NADPH. Recall that NADPH is a crucial electron carrier involved in biosynthetic reactions, which are used to build molecules and structures within the cell. The Entner-Doudoroff pathway only invests one ATP molecule, unlike the normal energy investment phase which usually invests 2 ATP molecules. Because the Entner-Doudoroff pathway only invests 1 ATP molecule, it only produces one G3P molecule instead of producing 2 G3P molecules like what the normal energy investment phase does. This one G3P made by the Entner-Doudoroff pathway can still continue in the energy harvest phase. Since there's only 1 G3P molecule produced in the Entner-Doudoroff pathway, the energy harvest phase will only produce half the amount of NADH and ATP as it normally does. Instead of producing 2 NADH and 2 net ATPs, it only produces 1 NADH and 1 net ATP in the Entner-Doudoroff pathway. Unlike normal glycolysis, the Entner-Doudoroff pathway produces NADPH, which is not made by the normal glycolysis pathway. This is an important feature that distinguishes the Entner-Doudoroff pathway from the normal energy investment phase.

If we take a look at our image below, we can get a better understanding of the Entner-Doudoroff pathway. The top half of the image represents the normal glycolysis pathway as we already learned it in our previous lesson videos. Essentially, this entire top half of the image should be a review for you from our previous lesson videos with no new information. The new information from this video is going to be in the bottom half of this image that represents the Entner-Doudoroff pathway. First, we will review the top half of the image with normal glycolysis. Normal glycolysis has 2 phases, the energy investment phase and the energy harvest phase. The intermediate between the two phases is G3P. Normal glycolysis starts with a glucose molecule that is converted into 2 pyruvate molecules. In the energy investment phase, 2 ATPs are used up to create these 2 G3P molecules. Then, each of these G3Ps undergoes reactions to create an NADH and 2 ATPs, so a total of 4 ATPs and 2 NADHs are made in the process of making 2 pyruvates. In terms of the products of the normal glycolysis, there are 0 NADPH molecules made, 2 G3P molecules made, 2 NADH electron carriers made, 2 net ATPs made (since 4 are made in the energy harvest phase and 2 are burnt up in the energy investment phase), and 2 pyruvates are ultimately produced. The bottom half of the image focuses on the Entner-Doudoroff pathway. This pathway uses only one ATP molecule to create only 1 G3P, so instead of 2 G3Ps, only 1 G3P is made. That 1 G3P will filter into the energy harvest phase to create only 1 NADH and 2 total ATPs. Despite the different pathways, a total of 2 pyruvates still result. One key distinction of the Entner-Doudoroff pathway is the production of 1 NADPH, which is significant since no NADPH is made in the normal pathway. Essentially, everything except the number of pyruvates remains the same in the final tally between the products of the normal pathway and the Entner-Doudoroff pathway. The Entner-Doudoroff pathway produces NADPH, which is used for biosynthetic reactions. The differences between the normal pathway and the products of the Entner-Doudoroff pathway mainly consist of the reduction of quantities except for the number of pyruvates, which remains the same.

This concludes our brief introduction to the Entner-Doudoroff pathway, which is used only by some bacteria but not eukaryotes, and does so mainly to create NADPH for biosynthetic reactions. We'll be able to get some practice applying these concepts as we move forward in our course. I'll see you all in our next video.

The Entner-Doudoroff Pathway:

• A. Converts glucose to pyruvate.
• B. Can operate aerobically or anaerobically.
• C. Is an alternative process to the glycolytic pathway.
• D. All the above are correct.

The Entner-Doudoroff pathway leads to the formation of:

• A. ATP.
• B. Pyruvate.
• C. NADH.
• D. NADPH.
• E. All of the above.

Here’s what students ask on this topic:

What is the Entner-Doudoroff pathway and how does it differ from glycolysis?

The Entner-Doudoroff pathway (EDP) is an alternative glycolytic pathway used by some bacteria, but not by eukaryotes. Unlike the traditional glycolysis pathway, which has an energy investment phase requiring 2 ATP molecules, the EDP only invests 1 ATP molecule. This results in the production of one glyceraldehyde-3-phosphate (G3P) molecule, leading to the generation of one NADH and one net ATP during the energy harvest phase. A key distinguishing feature of the EDP is the production of NADPH, an important electron carrier for biosynthetic reactions, which is not produced in traditional glycolysis. Both pathways ultimately generate two pyruvate molecules, but the EDP is less efficient in terms of NADH and ATP production.

Why is NADPH important in the Entner-Doudoroff pathway?

NADPH is a crucial product of the Entner-Doudoroff pathway because it serves as an important electron carrier involved in biosynthetic reactions. These reactions are essential for building molecules and structures within the cell. Unlike NADH, which is primarily used in energy production, NADPH provides the reducing power needed for anabolic processes, such as fatty acid synthesis and nucleotide synthesis. The production of NADPH in the EDP distinguishes it from the traditional glycolysis pathway, which does not produce NADPH.

Which organisms utilize the Entner-Doudoroff pathway?

The Entner-Doudoroff pathway is utilized by some bacteria, including both Gram-negative and Gram-positive species. Examples of bacteria that use this pathway include Pseudomonas, Azotobacter, and Zymomonas. This pathway is not found in eukaryotes. The EDP allows these bacteria to metabolize glucose and other carbohydrates efficiently, especially in environments where the traditional glycolysis pathway may not be as advantageous.

How does the ATP yield of the Entner-Doudoroff pathway compare to glycolysis?

The ATP yield of the Entner-Doudoroff pathway is lower compared to traditional glycolysis. In the EDP, only one ATP molecule is invested, resulting in the production of one glyceraldehyde-3-phosphate (G3P) molecule. This leads to the generation of one NADH and one net ATP during the energy harvest phase. In contrast, traditional glycolysis invests two ATP molecules and produces two G3P molecules, leading to the generation of two NADH and a net gain of two ATP molecules. Therefore, the EDP produces half the amount of NADH and ATP compared to glycolysis.

What are the main products of the Entner-Doudoroff pathway?

The main products of the Entner-Doudoroff pathway include one NADPH, one NADH, one net ATP, and two pyruvate molecules. The production of NADPH is a key distinguishing feature of the EDP, as it is not produced in traditional glycolysis. NADPH is essential for biosynthetic reactions, providing the reducing power needed for anabolic processes. The pathway also produces one NADH and one net ATP, which are used in cellular energy production. Despite the lower efficiency in terms of NADH and ATP production, the EDP still generates two pyruvate molecules, similar to glycolysis.