Section 2.5 Enzymes Introduction Chemical reactions require the addition of energy, called activation energy, to take place. Even if a chemical reaction starts, it may not happen very quickly. However, both the activation energy and the rate of a chemical reaction can be changed by a chemical catalyst. A catalyst is a substance that decreases the activation energy for a reaction and increases the rate of the reaction. In living things, enzymes are catalysts for chemical reactions. Almost all enzymes are proteins, and almost every process in living things needs enzymes. The function of each enzyme depends on its structure. A change in biological conditions within an organism can affect the shape of an enzyme, which can decrease or prevent an enzyme from working properly. For example, enzymes function best in a small range around an organism's normal temperature and pH. The shape of an enzyme is important because it allows only certain molecules to bind to the enzyme. The specific molecules that an enzyme acts on are called substrates. One way to think of enzyme function is called the lock-and-key model. Substrates bind to an enzyme like the way in which a key fits into a lock, so if an enzyme's structure changes, the substrates cannot bind to the enzyme. Here's how it works: 1. Substrates bind to an enzyme. The enzyme brings molecules close together so that they can react with one another. 2. The bonds inside the substrates are stretched slightly out of position, which weakens the bonds. Less energy is needed to break weaker bonds. 3. The reaction takes place and the product is released from the enzyme. The enzyme can then bind to more of the substrate molecules.
1. What is a catalyst?
2. Where are enzymes found?
3. How does an enzyme work?
