Back to: MICROBIOLOGY 200 LEVEL
Welcome to class!
Hello my science champion! I’m so glad you showed up again today. You’re growing stronger in your understanding of microbiology, and today’s lesson will take you even further. We’re going to look at two special pathways that microbes use to break down glucose and get energy: the Entner-Doudoroff (ED) pathway and the Pentose Phosphate (PP) pathway. Don’t worry if they sound a bit technical—together, we’ll break them down in a simple, practical, and relatable way. Let’s begin!
Entner-Doudoroff And Pentose Phosphate Pathways
Why Do We Need Other Pathways Besides Glycolysis?
Remember glycolysis? That’s the common way many organisms break down glucose. But not all microbes use glycolysis. Some bacteria, especially those in different environments or with unique needs, use other routes like the Entner-Doudoroff and Pentose Phosphate pathways to get energy and building blocks for survival.
Let’s understand them one by one.
Entner-Doudoroff (ED) Pathway
The Entner-Doudoroff pathway is another way of breaking down glucose to form pyruvate, just like glycolysis, but it’s less efficient in terms of energy.
It is found mostly in some Gram-negative bacteria, like Pseudomonas, Rhizobium, and Agrobacterium.
Instead of the regular glycolysis steps, it uses different enzymes to convert glucose to pyruvate and glyceraldehyde-3-phosphate (G3P).
The G3P then continues through part of glycolysis to form ATP and NADH.
Energy Yield:
1 ATP
1 NADH
1 NADPH
(from each glucose molecule)
This is less ATP than glycolysis, but the pathway also produces NADPH, which is useful for biosynthesis (building molecules in the cell).
Think of glycolysis as the main road to your village—it’s fast and smooth. But sometimes, if the main road is blocked, you take a smaller road. It’s slower, but you’ll still reach home. The ED pathway is that smaller road—less energy, but it still works!
Pentose Phosphate (PP) Pathway
The Pentose Phosphate pathway is also called the hexose monophosphate shunt. It doesn’t focus on producing a lot of ATP but is very important for making other molecules the cell needs.
Key purposes of the PP pathway:
Produces NADPH – needed for making fats and other building blocks.
Produces ribose-5-phosphate – needed to make DNA and RNA.
Provides sugar molecules used in various biosynthetic reactions.
The pathway starts with glucose-6-phosphate (from glucose), and through several steps:
NADPH is generated.
Sugars with 5, 7, and 4 carbon atoms are made and shuffled around.
Eventually, some products return to glycolysis.
Imagine a bakery: glycolysis is the worker baking bread (energy), but the PP pathway is the worker preparing special icing sugar, packaging, and labels. You may not get bread (ATP), but you get what you need to build a quality product (DNA, fats, etc.).
Summary
- The Entner-Doudoroff pathway is an alternative to glycolysis found in some bacteria. It makes 1 ATP, 1 NADH, and 1 NADPH.
- The Pentose Phosphate pathway helps make NADPH and ribose-5-phosphate for biosynthesis, not for energy.
- Both pathways support the cell in different ways: ED provides some energy and reducing power; PP is essential for making building blocks like DNA and fats.
- These pathways show how versatile microbes are—they always find a way to survive and grow!
Evaluation
- Which pathway produces both NADPH and ribose-5-phosphate?
- What is the ATP yield of the Entner-Doudoroff pathway?
- Give one example of a bacterium that uses the ED pathway.
- Why is the PP pathway important for biosynthesis?
You’ve just learned how microbes use different paths to survive—how cool is that? Your brain is doing something amazing, and I’m so proud of you. Just like microbes adapt and thrive using different routes, you too have what it takes to succeed in many ways. Keep learning, keep shining, and remember, with Afrilearn, you’re never alone on your journey. See you in the next lesson, superstar!