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Module 2D - Energy and Metabolism Objective # 19 All living organisms require energy for survival. In this module we will examine some general principles about chemical reactions and energy usage within cells. Define the term “energy” and distinguish g between potential and kinetic energy. 1 2 Objective 19 Objective 19 Energy is the ability to cause change. Any change in the universe requires energy. Energy comes in 2 forms: ¾ Potential energy g is stored energy. g No change is currently taking place ¾ Kinetic energy is currently causing change. This always involves some type of motion. Two Forms of Energy Potential energy Kinetic energy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3 Objective # 20 4 Objective 20 Thermodynamics State the first and second laws of thermodynamics and explain h they how h apply l to liliving i organisms. is the study of energy changes. Two fundamental laws govern all energy changes in the universe. These 2 laws are simply called the first and second laws of thermodynamics: 5 6 1 Objective 20 Objective 20 First Law: ¾ Energy can be converted from one form to another, but it cannot be created or destroyed. ¾ The total amount of energy in a closed system remains constant. Second Law: ¾ Whenever an energy conversion takes place, some of the energy gets p and converted into a more dispersed less useful form (usually random molecular motion = heat). 7 8 Objective 20 Objective 20 Free energy (G) is a measure of the amount of energy available to do useful work. It depends on: ¾ the total amount of energy g present; p this is called enthalpy (H) ¾ the amount of energy being used for non--useful work (random molecular non motion); this is called entropy (S). In 9 Objective 20 summary, whenever an energy change takes place in a closed system, ¾ the first law tells us the total energy remains constant ¾ the h second d llaw tells ll us ffree energy decreases. How is this possible? ¾ entropy increases! So closed systems tend to become more disorganized. general, ΔG = ΔH - T ΔS, where T represents the temperature in degrees Kelvin and Δ represent “the change in”. This means the amount of energy available for useful work (G) equals the total energy present (H) minus the energy that is being wasted on random molecular motion (S). 10 Objective # 21 In Explain what a chemical reaction is and discuss how chemical h i l equations i are used d to describe the changes that take place during a chemical reaction. 11 12 2 Objective 21 of the changes that take place in living organisms are the result of chemical reactions. What is a chemical reaction? ¾ As atoms and molecules move around, they collide with each other. If they collide with enough force, existing chemical bonds can break and new bonds can form. Objective 21 Most Chemical equations can be used to describe the changes that take place during a chemical reaction: CH4 + 2O2 C Reactants CO2 + 2H2O C Products During a chemical reaction no atoms are created or destroyed. 13 14 Objective 21 Objective # 22 Most reactions are reversible: ¾ reading from left to right is called the forward reaction ¾ reading ead g from o right g t to left e t iss called ca ed the t e reverse reaction At equilibrium equilibrium,, the rate of the forward reaction equals the rate of the reverse reaction. Distinguish between endergonic and exergonic reactions and explain how they are coupled in living organisms. Describe the roles of ATP and ADP in the coupling of chemical reactions. 15 16 Objective 22 Objective 22 All atoms and molecules have a certain amount of free energy: ¾ potential energy stored in the chemical bonds that hold them together. g ¾ kinetic energy due to their constant random motion. Large, complex molecules have more free energy than small molecules. Chemical reactions involve a change in free energy as well as a change in the types of molecules present. present 17 18 3 Objective 22 Objective 22 Exergonic reactions:: reactions the reactants have more free energy than the products: C6H12O6 + 6O2 → 6CO2 + 6H2O more free f energy l free less f energy involve a net release of energy and/or an increase in entropy occur spontaneously (without a net input of energy) Endergonic reactions:: reactions the reactants have less free energy than the products: 6CO2 + 6H2O → C6H12O6 + 6O2 less free energy more free energy involve a net input of energy and/or a decrease in entropy do not occur spontaneously 19 20 Objective 22 Energy released E Energy supplied Exergonic and Endergonic Reactions Living Product Energy must be supplied. Reactant Reactant Energy is released. Product Endergonic Exergonic 21 organisms have the ability to couple exergonic and endergonic reactions: ¾ energy g released by exergonic g reactions is captured and used to make ATP from ADP and Pi ¾ ATP can be broken back down to ADP and Pi, releasing energy to power the cell’s endergonic reactions. 22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ATP Adenosine triphosphate The “energy currency” for all cells Composed of Structure of ATP ¾ Ribose – 5 carbon sugar ¾ Adenine ¾ Chain of 3 phosphates Key to energy storage Bonds are unstable ADP – 2 phosphates AMP – 1 phosphate – lowest energy form 23 24 4 Objective # 23 The ATP Cycle Explain the concepts of chemical equilibrium, transition state, andd activation i i energy. 26 25 Objective 23 reactions, both endergonic and exergonic, require an input of energy to get started. This energy is called activation energy. energy. Activation A i i energy iis needed d d to b bring i the h reactants close together and weaken existing bonds. This produces an unstable state of maximum potential energy called the transition state. state. Energy released Energy supplied All Transition State Activation energy Reactant Product 27 28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Objective # 24 Objective 24 In most cases, molecules do not have enough kinetic energy to reach the transition state when they collide. Therefore, most collisions are nonnonproductive, and the reaction proceeds very slowly if at all. What can be done to speed up these reactions? Describe some methods that p up p can be used to speed chemical reactions. 29 30 5 Objective 24 Activation Energy and Catalysis Energy released Energy supplied 1) Add Heat – molecules move faster so they collide more frequently and with greater force. 2) Add a catalyst – a catalyst reduces the energy needed to reach the activation state, without being changed itself. Proteins that function as catalysts are called enzymes. enzymes. Activation energy Activation energy Reactant Reactant Product Product Uncatalyzed Catalyzed Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 31 Objective 24 32 Objective # 25 Unlike heat, which speeds up all reactions indiscriminately, enzymes are highly specific. Each enzyme typically speeds up only one or a few similar chemical reactions. Therefore, by controlling which enzymes are made, a cell can control which reactions take place in the cell. Describe the structure, function,, and characteristics of enzymes. 33 34 Objective 25 Objective 25 Almost all enzymes are globular proteins with one or more pockets on their surface called active sites. sites. Reactants bind to the active site to form an enzyme enzyme--substrate complex. complex. The 33-D shape of the active site and the substrates must match, like a lock and key. Binding of the substrates causes the enzyme to adjust its shape slightly, leading to a better induced fit fit.. When this happens, pp the substrates are brought close together and existing bonds are stressed. This reduces the amount of energy needed to reach the transition state. 35 36 6 Binding of the substrates causes the enzyme to adjust its shape slightly, leading to a better induced fit. 37 38 Objective # 26 Explain how the following factors can affect enzyme activity: a) temperature b) pH c) inhibitors and activators d) cofactors 39 Objective 26 40 Objective 26a & b The rate of an enzyme enzyme--catalyzed reaction is affected by the concentration of both the enzyme and its substrates. In addition, any physical or chemical factors that affect the enzyme’s 33-D shape can affect the enzyme’s ability to catalyze the reaction Temperature and pH: ¾ Most enzymes have an optimum temperature and an optimum pH. These are related to the environment where the enzyme normally functions. ¾ Enzyme activity decreases above or below the optimum. 41 42 7 Relationship of Enzyme Activity to pH Optimum temperature for human enzyme 30 40 50 Optimum temperature for enzyme from hotsprings prokaryote 60 70 Optimum pH for pepsin Optimum pH for trypsin Rate of Re eaction Rate o of Reaction Relationship of Enzyme Activity to Temperature 80 1 Temperature of Reaction (oC) 2 3 4 5 6 7 8 9 pH of Reaction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 43 44 Objective 26c Objective 26c Inhibitors and activators are substances that bind to an enzyme and affect its ability to catalyze a reaction. Activators bind to a region of the enzyme called the allosteric site, site, thereby maintaining the enzyme’s active configuration and its activity. Inhibitors 45 decrease enzyme activity in one of 2 ways: 1)competitive 1) competitive inhibitors bind to the active site, thereby p preventingg the substrates from binding. 2)noncompetitive 2) noncompetitive inhibitors bind to an allosteric site, thereby altering the shape of the active site so that it cannot bind to the substrate. 46 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Substrate Active site Substrate Inhibitor Active site Inhibitor Enzyme Enzyme Allosteric site When an inhibitor binds to the active site of an enzyme and blocks the substrate from binding, this is called… When an inhibitor joins to an allosteric site and alters the shape of the active site so it cannot bind to the substrate, this is called… Noncompetitive inhibition 47 Competitive inhibition 48 8 Objective 26d Objective # 27 Cofactors are nonprotein substances required by enzymes in order to function. For example, the active site of many enzymes contain metal ions that help draw electrons away from the substrates. Organic molecules that function as cofactors are called coenzymes. coenzymes. Define the terms “metabolism” and “metabolic pathway” (or “bi h i l pathway”) “biochemical h ”) andd explain how metabolic pathways are regulated. 49 50 Objective 27 refers to the sum of all chemical reactions carried out by an organism: ¾ reactions that jjoin small molecules together to form larger, more complex molecules are called anabolic. anabolic. ¾ reactions that break large molecules down into smaller subunits are called catabolic.. catabolic Objective 27 Metabolism A sequence of chemical reactions, where the product of one reaction serves as a substrate for the next, is called a metabolic pathway (or biochemical pathway). pathway). Most metabolic pathways take place in specific regions of the cell. 51 52 Objective 27 The regulation of simple metabolic pathways often depends on feedback inhibition:: inhibition ¾ the end p product of the p pathway binds to an allosteric site on the enzyme that catalyzes the first reaction and inactivates it. Why is the first reaction targeted? 53 54 9 55 10