Enzymes Notes

How Do Cells Control All These Reactions?

1. Cells control reactions using enzymes, which lower the activation energy needed for molecules to react.
2. Without enzymes, most reactions inside cells would happen far too slowly for life to function.
3. Enzymes allow cells to decide when, where, and how fast specific reactions occur.

How Do Enzymes Work?

1. Enzymes are proteins folded into a very specific three-dimensional shape.
2. A small part of the enzyme forms the active site, where the substrate binds.
3. Only substrates with the correct shape and chemical properties can bind, this feature is known as specificity.
4. When the substrate enters the active site, they form an enzyme–substrate complex.
5. Inside the active site, the enzyme weakens certain bonds or positions molecules so they react more easily.
6. The reaction reaches the transition state with much less energy than normal.
7. Products leave the active site, and the enzyme remains unchanged and ready to catalyze the next reaction.

What Makes the Active Site So Effective?

1. When the substrate binds, the enzyme tightens around it to improve contact.
2. This tightening is called induced fit, and it positions key chemical groups exactly where they need to be.
3. Better alignment reduces the activation energy and makes it easier for bonds to break or form.
4. Once products are released, the active site returns to its original shape.

How Do Enzymes Lower Activation Energy?

1. Enzymes speed reactions by:
   1. Bringing reactants together so they collide in the correct orientation.
   2. Applying strain to bonds, making them easier to break.
   3. Stabilizing the transition state, so less energy is required to reach it.
   4. Creating a helpful microenvironment, such as acidic or charged conditions inside the active site.
   5. Providing an alternative reaction pathway with a lower activation energy.

Why Do Enzymes Only Work With Certain Substrates?

1. The shape of the active site is determined by the enzyme’s tertiary structure.
2. Even small changes in amino acid sequence can alter the active site shape.
3. If the substrate doesn't fit, it can't bind, and no reaction occurs.
4. This prevents unwanted reactions and keeps cell chemistry under control.