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Biology A Guide to the Natural World Chapter 6 • Lecture Outline Life’s Mainspring: An Introduction to Energy Fifth Edition David Krogh © 2011 Pearson Education, Inc. 6.1 Energy Is Central to Life © 2011 Pearson Education, Inc. Energy Is Central to Life • All living things require energy. • The sun is the ultimate source of energy for most living things. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 6.2 The Nature of Energy © 2011 Pearson Education, Inc. The Nature of Energy • Energy can be defined as the capacity to bring about movement against an opposing force. © 2011 Pearson Education, Inc. Forms of Energy • Energy can be conceptualized as either potential energy, meaning stored energy; or kinetic energy, meaning energy in motion. © 2011 Pearson Education, Inc. Thermodynamics • The study of energy is known as thermodynamics. • The laws of thermodynamics are fundamental principles of energy. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. Tranformations of Energy • Entropy is a measure of the amount of disorder in a system; the greater the entropy, the greater the disorder. © 2011 Pearson Education, Inc. Transformations of Energy 3. Mechanical energy 2. Heat energy piston-driven flywheel heat coal 1. Chemical bond energy heat steam motion Total energy is constant. Entropy increases. © 2011 Pearson Education, Inc. Figure 6.2 6.3 How Is Energy Used by Living Things? © 2011 Pearson Education, Inc. How Is Energy Used by Living Things? • Living things can bring about local increases in order (in themselves) through their metabolic processes. © 2011 Pearson Education, Inc. Macromolecular Synthesis • They can, for example, build up moreordered molecules (starches, proteins) from less ordered molecules (simple sugars, amino acids). • However, it takes energy to do this. © 2011 Pearson Education, Inc. 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). © 2011 Pearson Education, Inc. Endergonic and Exergonic Reactions • Conversely, energy is released in exergonic (downhill) reactions, in which the reactants contain more energy than the products. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. Endergonic and Exergonic Reactions • Conversely, the breakdown of a complex carbohydrate into simple sugars is an exergonic reaction. • Such a reaction releases energy. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. Energy Stored and Released Product (glycogen) contains more energy than the reactants (glucose) glycogen molecule endergonic reaction energy in energy out exergonic reaction glucose molecules © 2011 Pearson Education, Inc. Product (glucose) contains less energy than the reactants (glycogen) Figure 6.4 ATP • The molecule most often used in living things to power coupled reactions is ATP. © 2011 Pearson Education, Inc. 6.4 The Energy Dispenser: ATP © 2011 Pearson Education, Inc. The Energy Dispenser: ATP • Adenosine triphosphate (ATP) is the most important energy transfer molecule in living things. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. The ATP/ADP Cycle • ATP drives chemical reactions by donating its third phosphate group to them. • In the process, it becomes the twophosphate molecule adenosine diphosphate (ADP). © 2011 Pearson Education, Inc. The ATP/ADP Cycle © 2011 Pearson Education, Inc. Figure 6.6 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. © 2011 Pearson Education, Inc. Energy and Biology Animation 6.1: Energy and Biology © 2011 Pearson Education, Inc. 6.5 Efficient Energy Use in Living Things: Enzymes © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. Enzymes • The substance that an enzyme helps transform through chemical reaction is called its substrate. • Lactose is the substrate of the enzyme lactase. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. Enzyme Action enzyme A enzyme B substrates enzyme C product © 2011 Pearson Education, Inc. Figure 6.8 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. © 2011 Pearson Education, Inc. 6.6 Enzymes and the Activation Barrier © 2011 Pearson Education, Inc. Enzymes and the Activation Barrier • Enzymes work by lowering activation energy, which is the energy required to initiate a chemical reaction. © 2011 Pearson Education, Inc. Enzymes Accelerate Chemical Reactions (a) Without enzyme lactose glucose + galactose activation energy without enzyme net energy released from splitting of lactose (b) With enzyme lactase lactose glucose + galactose activation energy with enzyme net energy released © 2011 Pearson Education, Inc. Figure 6.9 Enzymes Accelerate Chemical Reactions • Enzymes are catalysts. • They bring about a change in their substrates without being chemically altered themselves. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. Substrate Binding © 2011 Pearson Education, Inc. Figure 6.10 Substrate Binding • Only a few of the hundreds of amino acids that typically make up an enzyme will be involved in substrate binding. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 6.7 Regulating Enzymatic Activity © 2011 Pearson Education, Inc. Regulating Enzymatic Activity • Enzyme activity can be controlled in several ways. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. 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. © 2011 Pearson Education, Inc. Allosteric Regulation (a) Substrate becomes product. 1 2 substrate enzyme 1. Substrate binds to enzyme. product 2. Enzyme transforms substrate to product. (b) Product feeds back on enzyme. 4 Shape change 3 3. Product binds to a different site on the enzyme, causing the enzyme to change shape. 4. The new shape of the enzyme prevents it from binding to any more substrate. © 2011 Pearson Education, Inc. Figure 6.12 Enzymes Overview Animation 6.2: Enzymes © 2011 Pearson Education, Inc.