Concept 5.5 Summary

To start a chemical reaction, it is first necessary to weaken chemical bonds in the reactant molecules.

*When you start a chemical reaction, you need to provide "start-up" energy called activation energy in order to activate the reactants and trigger a chemical reaction.

Ways to provide activation energy:

1. heat up the mixture of molecules

-hotter molecules may collide with enough energy to weaken bonds

-cooler molecules colide with less energy

*BUT, heating up a cell would cause many unnecessary reactions to occur at once. (and some of them will destroy the cell's delicate structures.)

2. Using enzymes

-enzymes let reactions to occur at the cell's normal temperature (unlike heating up the molecules.) by lowering the energy requirement barrier. It means that the reaction needs less activation energy.

*Enzymes don't supply activation energy to the reacting molecules.

Enzyme-the main catalysts of chemical reactions in organisms

*catalysts-compounds that speed up chemical reactions

-specialized proteins

-each enzyme catalyzes a specific kind of chemical reaction.

-each catalyze only one type of reaction because te shape of each enzyme fits the shape of only particular reactant molecules.

Substrate-a specific reactant acted upon by an enzyme.

Active site-a particular region of the enzyme where it's substrate fits into.

-A substrate binds to an enzyme at an active site. The enzyme-substrate interaction lowers the activation energy required for the reaction to proceed. In this example, water is added to the weakend bond insucrose, breaking sucrose into glucose and fructose.

Concept Check 5.5

1. Explain the role of activation energy in a reaction. How does an enzyme affect activation energy?

Activation energy activates the reactants and triggers a chemical reaction. An enzyme let a molecule need less active energy to proceed a reaction by lowering the active energy requirement barrier in the molecule so that the reaction can proceed at normal cell temperatures.

2. Descrbie how a substrate interacts with an enzyme.

As the substrate enters, the active site changes shape slightly, fitting the substrate more snugly. ths places certain functional groups of the active site in position to catalyze the reaction. The tighter grip may also bend the substrate, weaening its bonds.