Chapter 6 6.1 An Overview of Metabolism (p. 119-121) Metabolism is the set of biochemical reactions that transforms molecules and transfers energy. LO 6.1: Evaluate how the principles of energy flow affect living systems. Terminology: Adenosine triphosphate (ATP) Autotrophs Catabolism Phototrophs Heterotrophs Anabolism Chemotrophs Metabolism Self-Assessment Questions: 1. What is the difference between catabolism and anabolism? 6.2: Kinetic and Potential Energy (p. 119-123) Kinetic energy is energy of motion, and potential energy is stored energy. LO 6.2 : Contrast the two basic forms of energy, potential and kinetic energy. Terminology: Energy Kinetic energy Potential energy Chemical energy Self-Assessment Questions: 2. Describe kinetic and potential energy. Provide an example of each. 3. Draw the structure of ATP, indicating the bonds that are broken during hydrolysis. 6.3 Laws of Thermodynamics (p.123-124) The first and second laws of thermodynamics govern energy flow in biological systems. LO 6.3 : Evaluate how the laws of thermodynamics apply to biological systems. Terminology: First law of thermodynamics Second law of thermodynamics Entropy Self-Assessment Questions: 4. What are the first and second laws of thermodynamics and how do they relate to chemical reactions? 6.4 Chemical Reactions (p.124-127) Chemical reactions involved the breaking and forming of bonds. LO 6.4 : Explain the type(s) of energy involved in forming and breaking chemical bonds. Terminology: Gibbs free energy (G) Endergonic Exergonic Entropy (S) Self-Assessment Questions: 5. How can the hydrolysis of ATP drive non-spontaneous reactions in a cell? Energetic coupling 6.5 Enzymes and the Rate of Chemical Reactions (p.127-132) The rate of chemical reactions is increased by protein catalysts called enzymes. LO 6.5 Evaluate the role of enzymes in catalyzing chemical reactions. Terminology: Transition state Active site Allosteric enzymes Activation energy (EA) Inhibitors Negative feedback Substrate Activators Cofactor Self-Assessment Questions: 6. What are three characteristics of enzymes, and how does each permit chemical reactions to occur in cells? 7. Which of the following do enzymes change? ΔG, reaction rate, types of product, activation energy, the laws of thermodynamics? 8. How does protein folding allow for enzyme specificity? Answers to Self-Assessment Questions 1. 2. Catabolism is the set of chemical reactions that break down macromolecules into smaller units, releasing energy (ATP). Anabolism is the set of chemical reactions that build macromolecules from smaller units and require an input of energy (usually in the form of ATP). One form of energy is kinetic energy (the energy of motion). Examples of kinetic energy are flexing a muscle and throwing a ball. Another form of energy is potential energy (stored energy). Potential energy depends on the structure of the object or its position relative to its surroundings, and it is released by a change in the object’s structure or position. A ball sitting on the top of the stairs has a great deal of potential energy, which is released when the ball starts to roll down the stairs (at which point, the energy is converted into kinetic energy). 3. 4. 5. 6. 7. 8. See Figs. 6.5 and 6.6. The first law of thermodynamics is the law of conservation of energy. It states that energy can be neither created nor destroyed; it can only be transformed from one form into another. The second law of thermodynamics states that the transformation of energy is associated with an increase in the disorder of the universe. The degree of disorder is called entropy. Chemical reactions are subject to the laws of thermodynamics (like everything else). As a result, the total amount of energy remains the same before and after a chemical reaction, but some of the energy is used to increase the entropy of the system, and only some of the energy is available to do the work of the cell. The hydrolysis of ATP releases energy. This energy can be used to drive nonspontaneous reactions in a cell if the total ΔG for the entire pathway is negative. See Fig. 6.10. Enzymes reduce the activation energy of a chemical reaction (or the energy input necessary to reach the transition state) by stabilizing the transition state and decreasing its free energy. See Fig. 6.12. Enzymes are catalysts that participate in a chemical reaction, forming complexes with products and reactants, but are not themselves consumed in the process. Enzymes are also highly specific. They typically catalyze only one reaction, recognizing a specific substrate. Finally, inhibitors and activators can influence enzyme activity. Inhibitors decrease the activity of enzymes, whereas activators increase this activity. See Fig. 6.16 for an example of two different types of inhibitors. Enzymes increase the reaction rate and decrease the activation energy. Enzymes do not change the other parameters. An enzyme will only act on those substrates that bind to its active site (the portion of the enzyme that binds substrate and converts it to product). An enzyme has to fold into its correct shape for the active site to be the right shape to bind its substrate.
