C1.1.5 Interactions between substrate and active site to allow induced-fit binding Notes

Induced-Fit Binding: How Substrates and Active Sites Work Together

1. The induced-fit model is more flexible than the outdated lock-and-key model.
2. It explains how enzymes can adjust their shape to better accommodate substrates.
3. The lock-and-key model can be misleading because it suggests that enzymes are rigid and unchanging, which does not reflect the dynamic nature of enzyme-substrate interactions observed in reality.

Initial Contact: Substrate Approaches the Active Site

1. Random Movement: Substrates move randomly in their environment until they come close to an enzyme's active site.
2. Chemical Attraction: Weak interactions, such as hydrogen bonds or ionic interactions, draw the substrate toward the active site.

Shape Change: Enzyme and Substrate Adjust

1. Conformational Change: When the substrate binds, the enzyme undergoes a subtle change in shape. This change is called induced fit.
2. Substrate Adjustment: The substrate may also change shape slightly to fit more snugly into the active site.

Catalysis: Breaking and Forming Bonds

1. Strain on Bonds: The induced fit places stress on specific bonds within the substrate, making them easier to break.
2. Optimal Alignment: The enzyme positions the substrate in a way that lowers the activation energy needed for the reaction.
3. Reaction Occurs: Bonds in the substrate break, and new bonds form, converting the substrate into products.

Release and Reset: Returning to Original Shape

1. Product Release: Once the reaction is complete, the products have a different shape and chemical properties, causing them to detach from the active site.
2. Enzyme Resets: The enzyme returns to its original shape, ready to bind another substrate molecule.