1. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. BIOLOGY A GUIDE TO THE NATURAL WORLD FOURTH EDITION DAVID KROGH Life’s Mainspring: An Introduction to Energy

2. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 6.1 Energy is Central to Life

3. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Energy is Central to Life All living things require energy. The sun is the ultimate source of energy for most living things.

4. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Energy is Central to Life The sun’s energy is captured on Earth by photosynthesizing organisms (such as plants), which then pass this energy on to other organisms in the form of food.

5. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 6.2 The Nature of Energy

6. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Nature of Energy Energy can be defined as the capacity to bring about movement against an opposing force.

7. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Forms of Energy Energy can be conceptualized as either potential energy, meaning stored energy; or kinetic energy, meaning energy in motion.

8. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Thermodynamics The study of energy is known as thermodynamics. The laws of thermodynamics are fundamental principles of energy.

9. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Thermodynamics The first law of thermodynamics states that energy is never created or destroyed, but is only transformed. The second law of thermodynamics states that energy transfer will always result in a greater amount of disorder in the universe.

10. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Tranformations of Energy In line with the second law of thermodynamics, in every energy transaction, some energy will be lost to the most disordered form of energy, heat.

11. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Tranformations of Energy Thus, in the operation of a car engine, only part of the energy released by the combustion of gasoline actually helps propel the car; the rest of the energy released in the combustion is lost to heat.

12. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Tranformations of Energy Entropy is a measure of the amount of disorder in a system; the greater the entropy, the greater the disorder.

13. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Tranformations of Energy Figure 6.2 Total energy is constant. Entropy increases. piston-driven flywheel coalsteam heat motion 2.Heat energy 3.Mechanical energy 1.Chemical bond energy

14. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 6.3 How is Energy Used by Living Things?

15. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. How is Energy Used by Living Things? Living things can bring about local increases in order (in themselves) through their metabolic processes.

16. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Macromolecular Synthesis They can, for example, build up more-ordered molecules (starches, proteins) from less ordered molecules (simple sugars, amino acids). However, it takes energy to do this.

17. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Endergonic and Exergonic Reactions Energy in living things is stored away in endergonic (uphill) reactions in which the products of the reaction contain more energy than the starting substances (or reactants).

18. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Endergonic and Exergonic Reactions Conversely, energy is released in exergonic (downhill) reactions, in which the reactants contain more energy than the products.

19. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Endergonic and Exergonic Reactions The linkage of simple sugars to form a complex carbohydrate is an endergonic reaction. Such a reaction will not occur without an input of energy.

20. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Endergonic and Exergonic Reactions Conversely, the breakdown of a complex carbohydrate into simple sugars is an exergonic reaction. Such a reaction releases energy.

21. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Endergonic and Exergonic Reactions Endergonic and exergonic reactions are linked in coupled reactions—reactions in which an energy yielding exergonic reaction powers an energy-requiring endergonic reaction.

22. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Energy Stored and Released Figure 6.4 glycogen molecule energy out energy in glucose molecules Product (glycogen) contains more energy than the reactants (glucose). Product (glucose) contains less energy than the reactants (glycogen). endergonic reaction exergonic reaction

23. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. ATP The molecule most often used in living things to power coupled reactions is ATP.

24. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 6.4 The Energy Dispenser: ATP

25. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The Energy Dispenser: ATP Adenosine triphosphate (ATP) is the most important energy transfer molecule in living things.

26. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. ATP In animals, energy that is extracted from food is transferred to ATP, and this energy is then used to drive a vast array of metabolic processes. Energy supplied by ATP is used, for example, to power muscle contraction and nerve signal transmission.

27. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. ATP ATP’s energy transfer powers stem from the fact that it contains three phosphate groups, each of which is negatively charged, meaning these groups repel each other.

28. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The ATP/ADP Cycle ATP drives chemical reactions by donating its third phosphate group to them. In the process, it becomes the two-phosphate molecule adenosine diphosphate (ADP).

29. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The ATP/ADP Cycle Figure 6.6 phosphate groups adenosine ATP ADP H2OH2O+ energy out energy in endergonic reaction exergonic reaction adenine ribose

30. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. The ATP/ADP Cycle To again become ATP, it must have a third phosphate group attached to it. This shuttling back and forth between ATP and ADP takes place constantly in living things.

31. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Energy and Biology PLAY Animation 6.1: Energy and Biology

32. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 6.5 Efficient Energy Use in Living Things: Enzymes

33. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Efficient Energy Use in Living Things: Enzymes An enzyme is a type of protein that accelerates the rate at which a chemical reaction takes place in an organism.

34. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Enzymes Nearly every chemical process that takes place in living things is facilitated by an enzyme. For example, the enzyme lactase facilitates the splitting of the sugar lactose into its component sugars, glucose and galactose.

35. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Enzymes The substance that an enzyme helps transform through chemical reaction is called its substrate. Lactose is the substrate of the enzyme lactase.

36. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Enzymes Many activities in living things are controlled by metabolic pathways, in which a series of reactions is undertaken in sequence, each facilitated by its own enzyme. In such a series, the product of one reaction becomes the substrate for the next.

37. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Enzyme Action Figure 6.8 substrates enzyme A enzyme B enzyme C product

38. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Metabolism and Enzymes The sum of all the chemical reactions that a cell or larger living thing carries out is its metabolism. Enzymes are active in all facets of the metabolism of all living things.

39. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 6.6 Lowering the Activation Barrier through Enzymes

40. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Lowering the Activation Barrier through Enzymes Enzymes work by lowering activation energy, which is the energy required to initiate a chemical reaction.

41. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Enzymes Accelerate Chemical Reactions Figure 6.9 lactoseglucose + galactose activation energy without enzyme activation energy with enzyme net energy released from splitting of lactose net energy released lactose lactase glucose + galactose (a)Without enzyme (b)With enzyme

42. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Enzymes Accelerate Chemical Reactions Enzymes are catalysts. They bring about a change in their substrates without being chemically altered themselves.

43. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Enzymes Accelerate Chemical Reactions Enzymes generally take the form of globular or ball-like proteins whose shape includes a pocket into which the enzyme’s substrate fits. This pocket is the active site—that portion of an enzyme that binds with a substrate, thus helping transform it.

44. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Substrate Binding Figure 6.10

45. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Substrate Binding Only a few of the hundreds of amino acids that typically make up an enzyme will be involved in substrate binding.

46. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Substrate Binding In some cases, substrate binding is facilitated by coenzymes: molecules other than amino acids that facilitate the work of enzymes by binding with them.

47. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. 6.7 Regulating Enzymatic Activity

48. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Regulating Enzymatic Activity Enzyme activity can be controlled in several ways.

49. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Regulating Enzymatic Activity Competitive inhibition is a reduction in the activity of an enzyme by means of a compound other than the enzyme’s usual substrate binding with the enzyme in its active site.

50. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Regulating Enzymatic Activity Another means of control is allosteric regulation, in which a molecule binds with the enzyme at a site other than its active site. Such binding changes the enzyme’s shape, thereby decreasing or increasing the enzyme’s ability to bind with its substrate.

51. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Regulating Enzymatic Activity Because of such processes as allosteric regulation, enzymes are not fated to turn out product in strict accordance with the amount of substrate in their environment; rather, enzyme activity can be finely tuned in accordance with cellular needs.

52. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Allosteric Regulation Figure 6.12 product Substrate binds to enzyme. Enzyme transforms substrate to product. Product binds to a different site on the enzyme, causing the enzyme to change shape. 1. 2. 3. 4.The new shape of the enzyme prevents it from binding to any more substrate. enzyme substrate (a)Substrate becomes product (b)Product feeds back on enzyme Shape change

53. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings. Enzymes Overview PLAY Animation 6.2: Enzymes