Campbell Biology in Focus Third Edition Chapter 6 An Introduction to Metabolism The Energy of Life ● ● ● The living cell is a miniature chemical factory where thousands of reactions occur Cells extract energy from sugars using cellular respiration and apply that energy to perform work Some organisms, such as the firefly, even convert energy to light called bioluminescence Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved What Causes These Breaking Waves to Glow? Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved What Causes These Breaking Waves to Glow? Bioluminescent phytoplankton Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Metabolism METABOLISM = all the chemical reactions that occur in the body All reactions are catalyzed by enzymes Metabolic pathways are a series of steps that result in a specific product Each participant in the series of steps is called a metabolite Cellular respiration – food broken down to make ATP (energy) Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Catabolism ● ● Breakdown of large complex molecules into simpler, smaller ones Some of these reactions release chemical energy A portion of this energy is captured as ATP (40%) and the rest is released as heat ● Cells break down excess carbohydrates first, then lipids ● Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Anabolism ● The synthesis of complex molecules in living organisms from simpler ones: biosynthesis ● These reactions require chemical energy (ATP) ● Is NOT the reversal of catabolism ● Examples: ● ● ● amino acids join together to make proteins glucose joins together to make polysaccharides or glycogen glycerol reacts with fatty acids to make lipids Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved ENERGY ● Energy is fundamental to all metabolic processes ● Energy is the capacity to do work or cause change ● Energy exists in various forms, some of which can perform work ● ● ● ● Kinetic energy is energy associated with motion Thermal energy is kinetic energy associated with random movement of atoms or molecules Heat is thermal energy in transfer from one object to another Light is another type of energy Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Thermodynamics ● ● ● The study of energy transformations In an open system, energy and matter can be transferred between the system and its surroundings In an isolated system, exchange with the surroundings cannot occur Organisms are open systems Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved The First Law of Thermodynamics Energy can be transferred and transformed, but it cannot be created or destroyed (the energy of the universe is constant) Also called the principle of conservation of energy Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved The Second Law of Thermodynamics ● ● Every energy transfer or transformation increases the entropy of the universe Entropy is a measure of molecular disorder Every transfer or transformation of energy increases entropy because some energy is lost to the surroundings as heat ● Heat increases the disorder of the surroundings ● Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Thermodynamics ● ● ● Spontaneous processes occur without energy input; they can happen quickly or slowly For a process to occur spontaneously, it must increase the entropy of the universe Nonspontaneous processes lead to a decrease in entropy; energy must be supplied Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Order and Disorder (entropy) How the universe tends toward disorder: If you drop a box of crayons organized by color in a box, they don't stay organized as they fall and hit the floor. If you picked them back up and tossed them on the ground again they will never 'fall' back into order. If you walk long enough, your shoelaces will become untied. But they will never reverse, shoelaces won't tie themselves. It take energy (heat release) for you to re-tie your shoes. Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved ΔG = FREE ENERGY ● ● Free energy is the portion of a system’s energy that can do work when temperature and pressure are uniform throughout, as in a living cell Biologists measure changes in free energy to help them understand the chemical reactions of life ● The Free-Energy Change of a Reaction Tells Us Whether or Not the Reaction Occurs Spontaneously Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Free-Energy Change (ΔG) The change in free energy (ΔG) during a chemical reaction is the difference between the free energy of the final state and the free energy of the initial state DG = Gfinalstate – Ginitialstate Only reactions with a negative ΔG are spontaneous Unstable systems (higher G) tend to change such that they become more stable (lower G) Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved The concept of free energy can be applied to the chemistry of life’s processes ● ● ● ● An exergonic reaction proceeds with a net release of free energy and is spontaneous; ΔG is negative The magnitude of ΔG represents the maximum amount of work the reaction can perform An endergonic reaction absorbs free energy from its surroundings and is nonspontaneous; ΔG is positive The magnitude of ΔG is the quantity of energy required to drive the reaction Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Exergonic Reactions (a) Exergonic reaction: energy released, spontaneous Free energy Reactants Amount of energy released (DG < 0) Energy Products Progress of the reaction Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Endergonic Reactions (b) Endergonic reaction: energy required, nonspontaneous Free energy Products Reactants Energy Amount of energy required (DG > 0) Progress of the reaction Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Equilibrium and Metabolism ● Cells are not in equilibrium; they are open systems experiencing a constant flow of materials in and out Metabolism as a whole is never at equilibrium; one of the defining features of life ● ● A catabolic pathway in a cell releases free energy in a series of reactions The product of each reaction is the reactant for the next, preventing the system from reaching equilibrium Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved A multistep hydroelectric system – good analogy of cellular respiration DG < 0 DG < 0 DG < 0 Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved ATP Powers Cellular Work To do work, cells manage energy resources by energy coupling, the use of an exergonic process to drive an endergonic one Most energy coupling in cells is mediated by ATP Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved ATP Adenine Triphosphate group (3 phosphate groups) Ribose (a) The structure of ATP. Adenosine triphosphate Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Hydrolysis of ATP The bonds between the phosphate groups of ATP can be broken by hydrolysis ATP hydrolysis releases energy and produces ADP (adenosine diphosphate) and inorganic phosphate ATP hydrolysis releases a lot of energy due to the repulsive force of the three negatively charged phosphate groups The triphosphate tail of ATP is the chemical equivalent of a compressed spring Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved Hydrolysis of Adenosine Triphosphate (ATP) P P P Adenosine triphosphate (ATP) H2O P i P P Energy+ Inorganic phosphate Adenosine diphosphate (ADP) (b) The hydrolysis of ATP. The reaction of ATP and water yields inorganic phosphate ( P i) and ADP and releases energy. Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved How ATP Works The chemical work in a cell is powered by ATP hydrolysis The energy released by the exergonic reaction of ATP hydrolysis is used to drive endergonic reactions Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved How ATP Works (2 of 3) ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to another molecule, such as a reactant The recipient molecule is now called a phosphorylated intermediate Overall, the coupled reactions are exergonic Copyright © 2020, 2016, 2014 Pearson Education, Inc. All Rights Reserved
