Summary 5.5

In order to start a chemical reaction the chemical bonds in the reactant molecules have to be weakened. In this process it is required that energy is absorbed by the molecules. This "start-up" energy is referred to as activation energy, as it is the energy that activates the reactants and initiates a chemical reaction.

Cellular reactions rely on catalysts, compounds that speed up reactions. In the chemical reactions of organisms the main catalysts are specials proteins called enzymes. Enzymes do not supply activation energy, but lower the the energy required to start a reaction; thus, allowing reactions to occur faster at room temperature. Specific enzymes cause specific kinds of chemical reactions.

• if enzymes were to supply activation energy, the tempertaure would increase
  
• the lower the energy required to start a chemical reaction, the faster and more possibly it can occur
  

An enzyme catalyzes only one kind of reaction. The reason for this is that shape of each enzyme only fits the particular shape of reactant molecules. Furthermore, the reactant that is acted upon by the enzyme is defined as the enzyme's subtrate. The specific region in which the subtrate fits into is the activate site. The subratate's fit into the enzyme is not rigid. When a subtrate enters an enyzme, the enzyme slightly changes shape in order to fit the subrate snuggly.

Another way in which enzymes lower the activation energy is by accepting two subrates in adjacent areas. The holding of reactants together enables them to react more easily. Through this process, enzymes can catalyze the making of larger molecules from smaller molecules. Just like any protein, an enzyme's shape and structure are crucial to its functin. Furthermore, factors such as pH and temperature change can affect how an enzyme works, or if it works at all.

Concept Check

1. Explain the role of activation energy in a reaction. How does an enzyme affect activation energy? The role of activation energy in a reaction is that this is the initial energy with which a reaction starts. This energy activates reactants to start a chemical reaction. An enzyme lowers the activation energy, thus speeding up the chemical reaction.

2. Describe how a subtrate interacts with an enyzme. A subtrate interacts with an enzyme by entering the active site of the enzyme. The fit between the subtrate and the enzyme is not rigid, but instead the enzyme's active sight slightly changes shape to fit the subtrate.