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Science Question of the Day Explain why the chemical bonds in the body do

5. 3 Chemical Reactions Chemical reactions begin with reactants (substrates) which are converted to

Fig. 5. 4 Energy of Activation Extra energy required to destabilize chemical bonds and

Fig. 5. 4 Catalysts lower the activation energy of a reaction, and thus increase

5. 4 How Enzymes Work Enzymes are proteins that serve as catalysts They speed

Fig. 5. 5 Enzyme shapes determines its activity Changes upon binding of the substrate

Fig. 5. 6 How enzymes work Copyright ©The Mc. Graw-Hill Companies, Inc. Permission required

Fig. 5. 7 The catalytic cycle of an enzyme 1 The substrate, sucrose, consists

5. 5 Factors Affecting Enzyme Activity Enzyme activity is affected by any change in

Enzyme Activity Copyright ©The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display

Fig. 5. 8 Enzymes are sensitive to their environment Digests proteins in the stomach

5. 6 How Cells Regulate Enzymes A cell can control the activity of an

Fig. 5. 9 How cells control enzymes Copyright ©The Mc. Graw-Hill Companies, Inc. Permission

Enzyme inhibition occurs in two ways: Competitive inhibition - Inhibitor binds at the enzyme’s

Enzymes Reviewed Copyright ©The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display

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Please Take out the Following Pencil Science Journal Agendas Macromolecules Worksheet (Pass it forward if you have not done so already). Plan for the week Copyright ©The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display

Science Question of the Day Explain why the chemical bonds in the body do not break down, spontaneously, releasing all of their energy. Copyright ©The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display

5. 3 Chemical Reactions Chemical reactions begin with reactants (substrates) which are converted to products Exergonic reactions Products contain less energy than the reactants Endergonic reactions Products contain more energy than the reactants Copyright ©The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display

Fig. 5. 4 Energy of Activation Extra energy required to destabilize chemical bonds and so initiate a chemical reaction Copyright ©The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display

Fig. 5. 4 Catalysts lower the activation energy of a reaction, and thus increase its rate However, they cannot make an endergonic reaction exergonic Copyright ©The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display

5. 4 How Enzymes Work Enzymes are proteins that serve as catalysts They speed up chemical reactions within cells Enzymes bind a specific molecule and stress bonds to make a particular reaction more likely Active site Site on enzyme surface where reactant fits Binding site Site on reactant where enzyme binds Copyright ©The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display

Fig. 5. 5 Enzyme shapes determines its activity Changes upon binding of the substrate The substrate is now bound more intimately Lysozyme Copyright ©The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display

Fig. 5. 7 The catalytic cycle of an enzyme 1 The substrate, sucrose, consists Glucose Fructose of glucose and fructose bonded together. 2 The substrate binds to the enzyme, forming an enzymesubstrate complex. Bond 4 Products are H 2 O released, and the enzyme is free to bind other substrates. Active site Enzyme 3 The binding of the substrate and enzyme places stress on the glucose-fructose bond, and the bond breaks. Copyright ©The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display

5. 5 Factors Affecting Enzyme Activity Enzyme activity is affected by any change in condition that alters the enzyme’s 3 -D shape The structural bonds of enzymes are sensitive to changes in temperature and p. H Therefore, a temperature or p. H beyond the optimal range will cause the enzyme to denature Copyright ©The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display

Fig. 5. 8 Enzymes are sensitive to their environment Digests proteins in the stomach Digests proteins in the intestine Copyright ©The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display

5. 6 How Cells Regulate Enzymes A cell can control the activity of an enzyme by altering its shape Allosteric enzymes have shapes that can be altered by the binding of signal molecules These molecules bind to the allosteric site Repressors bind and repress enzyme activity Activators bind and restore or increase enzyme activity Copyright ©The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display

Enzyme inhibition occurs in two ways: Competitive inhibition - Inhibitor binds at the enzyme’s active site Noncompetitive inhibition - Inhibitor binds at the enzyme’s allosteric site Fig. 5. 10 Copyright ©The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display