Chapter 3.3b - Inhibitors | Cambridge A-Level 9700 Biology

Summary

This video explains the factors that influence enzymatic reactions, focusing on enzyme inhibitors. It covers two main types: competitive and non-competitive inhibitors. Competitive inhibitors, which resemble the substrate, bind to the enzyme's active site and can be reversed by increasing substrate concentration. Non-competitive inhibitors, which bind to the enzyme's allosteric site, change the enzyme’s shape and inhibit its function permanently. The video also touches on end-product inhibition, a form of reversible non-competitive inhibition, which regulates metabolic reactions in the body to maintain homeostasis. The content provides a detailed understanding of enzyme inhibition and its implications.

Takeaways

• 😀 Competitive inhibitors have a similar shape to the substrate and bind to the enzyme's active site, competing with the substrate.
• 😀 The binding of competitive inhibitors is reversible and can be overcome by increasing substrate concentration.
• 😀 When the substrate concentration is much higher than the inhibitor, the reaction rate returns to normal because the substrate outcompetes the inhibitor.
• 😀 Competitive inhibition leads to a higher K_m, indicating that more substrate is required to reach half the maximum reaction rate (V_max).
• 😀 The V_max remains unchanged in competitive inhibition, meaning the enzyme can still reach full reaction rate at high substrate concentrations.
• 😀 Non-competitive inhibitors bind to an allosteric site on the enzyme, changing its structure and altering the active site shape.
• 😀 Non-competitive inhibition can be irreversible (e.g., cyanide) or reversible (e.g., end-product inhibition).
• 😀 In irreversible non-competitive inhibition, the enzyme is permanently inactivated, and increasing substrate concentration cannot restore function.
• 😀 Irreversible non-competitive inhibitors lower V_max by reducing the number of functional enzymes available.
• 😀 End-product inhibition is a reversible form of non-competitive inhibition that helps regulate metabolic processes by preventing overproduction of a product.
• 😀 In the case of end-product inhibition, the product of a reaction binds to an enzyme earlier in the pathway, slowing or stopping further production in response to high product levels.

Q & A

What is the main focus of Chapter 3.3 in this script?

The main focus is on the factors affecting enzyme-catalyzed reactions, specifically enzyme inhibitors, which reduce the rate of these reactions.

What are enzyme inhibitors, and how do they affect enzyme reactions?

Enzyme inhibitors are molecules that bind to enzymes and reduce the rate of enzyme-catalyzed reactions. They can interfere by either blocking the active site or altering the enzyme’s structure.

What is a competitive inhibitor, and how does it function?

A competitive inhibitor is a molecule that has a shape similar to the substrate and competes for binding to the enzyme’s active site, thereby reducing the rate of the reaction.

How can competitive inhibition be overcome?

Competitive inhibition can be overcome by increasing the substrate concentration, which increases the chances of the substrate binding to the active site instead of the inhibitor.

What happens to the enzyme reaction rate at low substrate concentration in the presence of a competitive inhibitor?

At low substrate concentration, the competitive inhibitor is more likely to bind to the active site, reducing the rate of enzyme-substrate complex formation and thereby decreasing the reaction rate.

What is the effect of increasing substrate concentration on competitive inhibition?

Increasing the substrate concentration reduces the effect of competitive inhibition because the substrate has a higher chance of binding to the active site, outcompeting the inhibitor.

What does a graph of rate versus substrate concentration show in competitive inhibition?

In a graph of rate versus substrate concentration, the **Vmax** is the same with or without the inhibitor at high substrate concentrations. However, the **Km** increases in the presence of an inhibitor.

What is non-competitive inhibition, and how does it differ from competitive inhibition?

Non-competitive inhibition occurs when the inhibitor binds to an allosteric site, not the active site. This changes the enzyme’s shape and prevents the substrate from binding, unlike competitive inhibition where the inhibitor competes with the substrate for the active site.

How does irreversible non-competitive inhibition affect enzyme activity?

Irreversible non-competitive inhibition permanently alters the enzyme by binding to the allosteric site, changing the enzyme's structure. This prevents the enzyme from functioning and reduces the available active enzymes.

What is end-product inhibition, and how does it maintain homeostasis?

End-product inhibition is a form of reversible non-competitive inhibition where the final product of a metabolic pathway inhibits an enzyme earlier in the pathway, preventing overproduction and maintaining homeostasis.

How does the graph of non-competitive inhibition compare to competitive inhibition?

In non-competitive inhibition, the **Vmax** decreases because fewer active enzymes are available, while **Km** remains constant. In competitive inhibition, **Vmax** remains the same, but **Km** increases.

Why does the **Vmax** decrease in irreversible non-competitive inhibition?

The **Vmax** decreases in irreversible non-competitive inhibition because the enzyme's structure is permanently altered, reducing the number of functional enzymes available for the reaction.

What is the relationship between substrate concentration and enzyme activity in non-competitive inhibition?

In non-competitive inhibition, increasing substrate concentration has no effect on enzyme activity because the enzyme’s ability to bind the substrate is permanently altered by the inhibitor.