1. Chemical Reactions and Enzymes

2. Chemical Reactions Everything that happens in an organism – its growth, its reproduction, and even its movement – is based on chemical reactions. A chemical reaction is a process that changes one set of chemicals into another set of chemicals.

3. Some reactions occur slowly. –Ex: iron + oxygen  iron oxide (rust) –This chemical reaction that causes rust to form happens slowly over time. Other reactions however, happen quickly, like when hydrogen gas (H 2 ) is ignited in the presence of oxygen.

4. The elements or compounds that enter into a chemical reaction are known as reactants. The elements or compounds produced by a chemical reaction are known as products. Reactant A + Reactant B    Product

5. Chemical reactions always involve the breaking of bonds in reactants and the formation of new bonds in products. Example: Our cells constantly produce carbon dioxide (CO 2 ) which is then carried through the bloodstream to the lungs where it is expelled through exhalation. However, CO 2 is not very soluble in water, so a chemical reaction with water occurs to transform CO 2 into a highly soluble compound called carbonic acid (H 2 CO 3 ). This reaction is reversed in the lungs, and the CO2 is exhaled.

6. Energy in Reactions Energy is released or absorbed whenever chemical bonds form or are broken. Chemical reactions that release energy often occur spontaneously. Chemical reactions that absorb energy will not occur without a source of energy. The graph shows an endothermic (or energy absorbing) reaction. Notice that the products are on a higher energy level than the reactants.

7. This graph shows an example of an energy releasing (exothermic) reaction. The peak of each graph represents the energy needed for the reaction to go forward. The difference between this required energy and the energy of the reactants is the activation energy.

8. What significance do these energy changes have on living things? In order to stay alive, organisms need to carry out chemical reactions that require energy. Animals get their energy by eating and digesting energy rich compounds.

9. Even chemical reactions that release energy do not always occur spontaneously. For example, burning paper releases energy, but you still need a match or flame to start the fire. The energy that is needed to get a chemical reaction started is called activation energy.

10. Enzymes Some of the chemical reactions necessary for life are too slow or too energy consuming to be practically carried out in the body. However, these reactions are made possible by the use of a catalyst. Catalysts speed up the rate of a chemical reaction by lowering the reaction’s activation energy.

11. Enzymes are proteins that act as biological catalysts. They speed up chemical reactions that take place in cells. Enzymes are proteins that act as biological catalysts. Most enzymes end with the suffix – ase.

12. Enzymes are very specific, often only catalyzing one chemical reaction. Without the enzyme carbonic anhydrase, carbon dioxide would build up in the bloodstream faster than it could be removed.

13. Enzyme Action For a chemical reaction to take place, the reactants must collide with enough energy so that existing bonds will be broken and new bonds will be formed. Enzymes provide a site where reactants can be brought together to react. The reactants of enzyme-catalyzed reactions are known as substrates. The substrates bind to a site on the enzyme called the active site.

14. Notice the active site, substrates, and products. What do you think the function of this enzyme is? The active site and the substrate have complementary shapes, like a lock and key.

15. The enzyme and substrates come together and form the enzyme- substrate complex. Once the reaction is over, the products are released and the enzyme is free to bind to another substrate.

16. Enzymatic Regulation Cells can regulate the activities of enzymes in a variety of ways. Most cells contain proteins that help turn enzymes “on” and “off” according to the needs of the cell. Some of these regulation mechanisms include: pH changes Temperature changes