Chemical Reactions in Biological Systems Law of Conservation of Energy Biochemistry Chemical Reactions in Biological Systems Law of Conservation of Energy 2

Law of Conservation of Energy Biochemistry Law of Conservation of Energy 3

Biochemistry Matter Solid Liquid Gas 4

Biochemistry Matter Melting Point Boiling Point 5

Copyright Pearson Prentice Hall Chemical Reactions A process that changes one set of chemicals into another set of chemicals. Copyright Pearson Prentice Hall 6

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. 7

Endothermic Reactions Energy Changes Exothermic Reactions Chemical reactions that release energy often occur spontaneously. Endothermic Reactions Chemical reactions that absorb energy will not occur without a source of energy. 8

How would you reverse this reaction? When hydrogen gas reacts with oxygen to produce water vapor, it is an energy-releasing reaction in which energy is given off as heat. 2H2 + O2 2H2O How would you reverse this reaction? 9

Activation Energy Chemists call the energy that is needed to get a reaction started the activation energy. Chemical reactions that release energy often occur spontaneously. Chemical reactions that absorb energy will occur only with a source of energy. 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. 11

Enzymes are Biological Catalysts. Some chemical reactions are too slow to be of value. These chemical reactions are made possible by catalysts. Enzymes are Biological Catalysts. 12

Enzymes speed up chemical reactions that take place in cells. 13

The Enzyme-Substrate Complex 14

An Enzyme-Catalyzed Reaction The enzyme hexokinase converts the substrates glucose and ATP into glucose-6-phosphate and ADP. 15

Changes in temperature Enzyme or substrate concentrations Regulation of Enzyme Activity pH values Changes in temperature Enzyme or substrate concentrations 16

Quiz 5-1 17

The elements or compounds produced by a chemical reaction are known as reactants. enzymes. products. waste. 18

Chemical reactions always involve catalysts. enzymes. changes in energy. changes in the atomic number of the reactants. 19

The factor that prevents many energy-releasing reactions from occurring at relatively low temperatures is called catalytic energy. chemical bond energy. enzyme energy. activation energy. 20

Which of the following statements is true? All proteins are enzymes. All enzymes are catalysts. All catalysts are enzymes. All catalysts are proteins. 21

The enzyme is destroyed, and the cell must make another. What happens to an enzyme after the reaction it catalyzes has taken place? The enzyme is destroyed, and the cell must make another. The enzyme holds on to the product until another enzyme removes it. The enzyme is unchanged and ready to accept substrate molecules. The enzyme changes shape so it can accept a different kind of substrate. 22