BIOLOGY                       CONCEPTS & CONNECTIONS                                        Fourth EditionNeil A. Campbell...
HOW ENZYMES WORK5.5 Enzymes speed up the cell’s chemical reactions    by lowering energy barriers• For a chemical reaction...
• A protein catalyst called an enzyme can   decrease the energy barrier                              EA                   ...
EA                                                                                      without                           ...
5.6 A specific enzyme catalyzes each cellular    reaction• Enzymes are selective        – This selectivity determines whic...
• How an                                                                        Enzyme                                    ...
5.7 The cellular environment affects enzyme    activity• Enzyme activity is influenced by        – temperature        – sa...
5.8 Enzyme inhibitors block enzyme action• Inhibitors interfere with enzymes        – A competitive          inhibitor tak...
5.9 Connection: Some pesticides and antibiotics    inhibit enzymes• Certain pesticides are toxic to insects because  they ...
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Cell Transport

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Cell Transport

  1. 1. BIOLOGY CONCEPTS & CONNECTIONS Fourth EditionNeil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor CHAPTER 5 The Working Cell Modules 5.5 – 5.9 From PowerPoint® Lectures for Biology: Concepts & Connections Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
  2. 2. HOW ENZYMES WORK5.5 Enzymes speed up the cell’s chemical reactions by lowering energy barriers• For a chemical reaction to begin, reactants must absorb some energy – This energy is called the energy of activation (EA) – This represents the energy barrier that prevents molecules from breaking down spontaneouslyCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
  3. 3. • A protein catalyst called an enzyme can decrease the energy barrier EA Enzyme barrier Reactants 1 Products 2 Figure 5.5ACopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
  4. 4. EA without EA with enzyme Reactants enzyme Net change in energy Products Figure 5.5BCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
  5. 5. 5.6 A specific enzyme catalyzes each cellular reaction• Enzymes are selective – This selectivity determines which chemical reactions occur in a cellCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
  6. 6. • How an Enzyme (sucrase) Active site Substrate (sucrose) enzyme works Glucose Fructose 1 4 Enzyme available Products are with empty active released site 3 Substrate is 2 converted to products Substrate binds to enzyme with Figure 5.6 induced fit • The enzyme is unchanged and can repeat the processCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
  7. 7. 5.7 The cellular environment affects enzyme activity• Enzyme activity is influenced by – temperature – salt concentration – pH• Some enzymes require nonprotein cofactors – Some cofactors are organic molecules called coenzymesCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
  8. 8. 5.8 Enzyme inhibitors block enzyme action• Inhibitors interfere with enzymes – A competitive inhibitor takes Substrate Active site the place of a Enzyme substrate in the active site NORMAL BINDING OF SUBSTRATE – A noncompetitive Competitive inhibitor Noncompetitive inhibitor inhibitor alters an enzyme’s function by changing its shape ENZYME INHIBITION Figure 5.8Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
  9. 9. 5.9 Connection: Some pesticides and antibiotics inhibit enzymes• Certain pesticides are toxic to insects because they inhibit key enzymes in the nervous system• Many antibiotics inhibit enzymes that are essential to the survival of disease-causing bacteria – Penicillin inhibits an enzyme that bacteria use in making cell wallsCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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