BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Neil A. Campbell Jane B. Reece Lawrence G. Mitchell Martha R. Taylor From PowerPoint ® Lectures for Biology: Concepts & Connections CHAPTER 5 The Working Cell Modules 5.1 – 5.4

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Reactants and Products 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. Na + Cl NaCl reactants product

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings There are two types of chemical reactions: –Endergonic reactions absorb energy and yield products rich in potential energy Figure 5.3A Reactants Potential energy of molecules Products Amount of energy INPUT

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –Exergonic reactions release energy and yield products that contain less potential energy than their reactants Figure 5.3B Reactants Potential energy of molecules Products Amount of energy OUTPUT

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Activation Energy Chemical reactions that release energy do not always occur spontaneously. Chemists call the energy that is needed to get a reaction started the activation energy.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Activation energy is a factor in whether the overall chemical reaction releases or absorbs energy

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Lowering the activation energy has a dramatic effect on how quickly the reaction is completed

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Enzymes Some chemical reactions that make life possible are too slow or have activation energies that are too high to make them practical for living tissue. These chemical reactions are made possible by catalysts. An enzyme is a biological catalyst.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Catalyst A catalyst is a substance that speeds up the rate of a chemical reaction. Catalysts work by lowering a reaction's activation energy.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings ENZYME CHARACTERISTICS  Enzymes are proteins that act as biological catalysts.  Enzymes speed up chemical reactions that take place in cells.  Enzymes are very specific, generally catalyzing only one chemical reaction.  Enzymes are not altered in the chemical reaction  Enzymes act by lowering the activation energy.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Enzyme-Substrate Complex Enzymes provide a site where reactants can be brought together to react, reducing the energy needed for reaction. The reactants of enzyme-catalyzed reactions are known as substrates.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings An Enzyme-Catalyzed Reaction

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Regulation of Enzyme Activity Enzymes can be affected by any variable that influences a chemical reaction. Enzymes work best at certain pH values. Many enzymes are also affected by changes in temperature and salt concentration

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Addition to the Enzyme Lab Obtain 4 additional ml of hydrogen peroxide Label the test –tubes # 4 and # 5 Place liver soaked in lemon juice in test-tube #4 Place liver soaked in baking soda in test-tube #5 Place 2 ml of hydrogen peroxide into test-tube # 4 – observe results using the previous rating scale Place 2ml of hydrogen peroxide in test-tube # 5 – observe the results using the rating scale

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings LAB CONTINUED… Additional questions: Compare the results from test-tubes #4 and # 5 to the results from test-tube # 2, the uncooked liver. 5. Why are the results different? 6. What contributed to the change in results?