1. Chapter 8 An Introduction to Metabolism

2. Metabolism, Energy, and Life The chemistry of life is organized into metabolic pathways the totality of an organism’s chemical reactions is called metabolism metabolic pathways alter molecules in a series of steps

3. enzymes selectively accelerate each step

4. The Complexity of Metabolism

5. Catabolic pathways release energy by breaking down complex molecules to simpler compounds Anabolic pathways consume energy to build complicated molecules from simpler compounds

6. the energy released by catabolic pathways is used to drive anabolic pathways the principles that govern energy resources in chemistry, physics, and engineering also apply to bioenergetics, the study of how organisms manage their energy resources

7. Organisms Transform Energy Energy is the capacity to do work - to move matter against opposing forces energy is also used to rearrange matter

8. 1. Kinetic energy is the energy of motion objects in motion, photons, and heat are examples Forms of Energy

9. 2. Potential energy is the energy that matter possesses because of its location or structure (stored energy) (the capacity to do work) chemical energy is a form of potential energy in molecules because of the arrangement of atoms

10. Activation Energy energy needed to convert potential energy into kinetic energy Activation energy Potential energy

11. Energy can be converted from one form to another for example, as a boy climbs a ladder to the top of the slide he is converting his kinetic energy to potential energy

12. as he slides down, the potential energy is converted back to kinetic energy it was the potential energy in the food he had eaten earlier that provided the energy that permitted him to climb up initially

13. Cellular respiration and other catabolic pathways unleash energy stored in sugar and other complex molecules this energy is available for cellular work

14. the chemical energy stored on these organic molecules was derived primarily from light energy by plants during photosynthesis a central property of living organisms is the ability to transform energy

15. The energy transformations of life are subject to two laws of thermodynamics Thermodynamics is the study of energy transformations in this field, the term system indicates the matter under study and the surroundings are everything outside the system

16. A closed system, like a liquid in a thermos, is isolated from its surroundings

17. In an open system, energy (and often matter) can be transferred between the system and surroundings organisms are open systems they absorb energy – light or chemical energy in organic molecules – and release heat and metabolic waste products

18. 1st Law of Thermodynamics The first law of thermodynamics states that energy can be transferred and transformed, but it cannot be created or destroyed aka: the principle of Conservation of Energy

19. plants transform light to chemical energy; they do not produce energy

20. 2 nd Law of Thermodynamics The second law of thermodynamics states that every energy transformation must make the universe more disordered entropy is a quantity used as a measure of disorder, or randomness

21. the more random a collection of matter, the greater its entropy (the quantity of energy in the universe is constant, but its quality is not)

22. How does Life go against entropy? By using energy from the environment or external sources (e.g. food, light)

23. In most energy transformations, ordered forms of energy are converted at least partly to heat automobiles convert only 25% of the energy in gasoline into motion; the rest is lost as heat

24. the metabolic breakdown of food ultimately is released as heat even if some of it is diverted temporarily to perform work for the organism Heat is energy in its most random state

25. Free Energy the portion of a system’s energy that can perform work

26. Free Energy G = H – T S G = free energy of a system H = total energy of a system T = temperature in ° K S = entropy of a system

27. Free Energy of a System If the system has more free energy - it is less stable The greater the work capacity

29. Spontaneous Process if the system is unstable, it has greater tendency to change spontaneously to a more stable state this change provides free energy for work

30. Chemical Reactions are the source of energy for living systems are based on free energy changes

31. Organisms live at the expense of free energy Chemical reactions can be classified as either exergonic or endogonic based on free energy

32. An exergonic reaction proceeds with a net release of free energy and G is negative An endergonic reaction is one that absorbs free energy from its surroundings occur spontaneously store energy

33. Exergonic/Endergonic

34. Cellular respiration is exergonic C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O for each mole of glucose broken down by respiration 686kcal of energy are made available for work

35. Photosynthesis is endergonic, powered by the absorption of light energy sunlight provides a daily source of free energy for the photosynthetic organisms in the environment

36. nonphotosynthetic organisms depend on a transfer of free energy from photosynthetic organisms in the form of organic molecules

37. ATP powers cellular work by coupling exergonic reactions to endergonic reactions

38. A cell does three main kinds of work: 1. Mechanical work – beating of cilia, contraction of muscle cells, and movement of chromosomes

39. 2. Transport work – pumping substances across membranes against the direction of spontaneous movement

40. 3. Chemical work – driving endergonic reactions such as the synthesis of polymers from monomers

41. In most cases, the immediate source of energy that powers cellular work is ATP

42. ATP (adenosine triphosphate) is a type of nucleotide consisting of the nitrogenous base adenine, the sugar ribose, and a chain of three phosphate groups

43. the bonds between phosphate groups can be broken by hydrolysis hydrolysis of the end phosphate group forms adenosine diphosphate [ATP  ADP = P i ]

44. while the phosphate bonds of ATP are sometimes referred to as high- energy phosphate bonds, these are actually fairly weak covalent bonds

45. they are unstable, however, and their hydrolysis yields energy because the products are more stable

46. in the cell the energy from the hydrolysis of ATP is coupled directly to endergonic processes by transferring the phosphate group to another molecule this molecule is now phosphorylated and is more reactive

47. ATP is a renewable resource that is continually regenerated by adding a phosphate group to ADP the energy to support renewal comes from catabolic reactions in the cell

48. ATP Cycles energy released from ATP drives anabolic reactions energy from catabolic reactions “recharges” ATP

49. ATP Cycle

50. Example: In a working muscle cell the entire pool of ATP is recycled once each minute, over 10 million ATP consumed and regenerated per second per cell Humans use close to their body weight in ATP daily

51. ATP Works by energizing other molecules by transferring phosphate groups no ATP production equals quick death

52. Enzymes Enzymes speed up metabolic reactions by lowering energy barriers A catalyst is a chemical agent that changes the rate of a reaction without being consumed by the reaction

53. an enzyme is a catalytic protein enzymes regulate the movement of molecules through metabolic pathways chemical reactions between molecules involve both bond breaking and bond forming

54. Activation Energy (E A ) is the amount of energy necessary to push the reactants over an energy barrier

55. enzymes speed reactions by lowering activation energy

56. Enzymes are substrate specific A substrate is a reactant that binds to an enzyme (what the enzyme acts on) when a substrate, or substrates, binds to an enzyme, the enzyme catalyzes the conversion of substrate to the product

57. Example: Sucrase is an enzyme that binds to sucrose and breaks the disaccharide into fructose and glucose (enzyme names end in –ase)

58. Active Site the area of an enzyme that binds to the substrate structure is designed to fit the molecular shape of the substrate therefore, each enzyme is substrate specific

60. Models of How Enzymes Work 1. Lock and Key model 2. Induced Fit model

61. Lock and Key Model substrate (key) fits to the active site (lock) which provides a microenvironment for the specific reaction

62. Induced Fit Model substrate “almost” fits into the active site, causing a strain on the chemical bonds, allowing the reaction substrate active site

63. The active site is an enzyme’s catalytic center a single enzyme molecule can catalyze thousands or more reactions a second enzymes are unaffected by the reaction and are reusable

64. most metabolic enzymes can catalyze a reaction in both the forward and reverse direction

65. Factors that Affect Enzymes environment cofactors coenzymes inhibitors allosteric sites

66. Environment A cell’s physical and chemical environment affects enzyme activity each enzyme has an optimal temperature because pH also influences shape and therefore reaction rate, each enzyme has an optimal pH too

67. this falls between pH 6 – 8 for most enzymes however, digestive enzymes in the stomach are designed to work best at pH 2 while those in the intestine are optimal at pH 8, both matching their working environments

68. Cofactors Many enzymes require nonprotein helpers, cofactors, for catalytic activity some inorganic cofactors include zinc, iron, and copper

69. organic cofactors, coenzymes, include vitamins or molecules derived from vitamins

70. Enzyme Inhibitors Competitive – mimic the substrate and bind to the active site

71. Noncompetitive – bind to some other part of the enzyme

73. Allosteric Regulation the control of an enzyme complex by the binding of a regulatory molecule regulatory molecule may stimulate or inhibit the enzyme complex

74. Allosteric Regulation

75. Control of Metabolism is necessary if life is to function controlled by switching enzyme activity “off” or “on” or separating the enzymes in time or space

76. Types of Control Feedback Inhibition Structural Order

77. Feedback Inhibition when a metabolic pathway is switched off by its end product end product usually inhibits an enzyme earlier in the pathway

79. Structural Order separation of enzymes and metabolic pathways in time or space by the cell’s organization

80. example: enzymes of respiration within the mitochondria – if a cell had the same number of enzyme molecules but they were diluted throughout the entire volume of the cell, respiration would be very inefficient