🔗 Enzyme-Substrate Complex – How the Reaction Happens
Let’s break it down step-by-step:
- Substrate (the molecule that needs to be changed) fits into the enzyme’s active site (like a puzzle piece).
- This forms a temporary structure called the enzyme-substrate complex (ES complex).
- The enzyme stresses or bends bonds in the substrate.
- The activation energy drops.
- The substrate is converted into products.
- The enzyme lets go of the product and remains unchanged.
🧠 That means enzymes can be reused again and again!
🔄 Enzyme Action in Complex Pathways
In the body, reactions often don’t happen in isolation. They occur in steps, like a factory assembly line.
These chains of reactions are called metabolic pathways.
Examples:
- Respiration (breaking down food for energy)
- Photosynthesis (plants making food)
- Protein synthesis (making proteins)
Each step needs a different enzyme. The product of one step becomes the substrate for the next.
⚙️ Assembly Line Analogy:
In a car factory, one worker fits the wheels, the next one paints it, and another installs the engine.
Similarly, in the cell, each enzyme does one step, then passes the product to the next enzyme.
🔁 Feedback Inhibition – Self-Regulating the System
Sometimes, the cell makes enough of a final product. When that happens:
- The end product goes back and blocks the first enzyme.
- This stops the pathway and prevents waste.
This is called feedback inhibition.
🛑 Analogy:
Think of an oven baking cookies. When you’ve baked enough, the timer stops the oven.
Similarly, the end product tells the cell to stop producing more.
🧩 Models of Enzyme Action
There are two major models to explain how enzymes and substrates interact: