Lecture 6 Bioenergetics PDF

Energy and Metabolism BIOL 110 The green glowing spots on the outside of this Brazilian termite mound are larvae of the click beetle, Pyrophorus nyctophanus. Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved How do the laws of thermodynamics relate to...

Energy and Metabolism BIOL 110 The green glowing spots on the outside of this Brazilian termite mound are larvae of the click beetle, Pyrophorus nyctophanus. Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved How do the laws of thermodynamics relate to biological processes? Energy use by living things demonstrates the first law of thermodynamics – Energy can be transferred and transformed, but not created or destroyed The conversion of energy to thermal energy released as heat by living things demonstrates the second law of thermodynamics – Every energy transfer or transformation increases the entropy (disorder) of the universe Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved How do the laws of thermodynamics relate to biological processes? Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Learning Objectives Define metabolic pathway. Contrast catabolic and anabolic pathways. Define the term energy and contrast potential and kinetic energy. State the first and second laws of thermodynamics and discuss their applications to living organisms and to the ecosphere. Distinguish between endergonic and exergonic reactions and explain how they may be coupled so that the second law of thermodynamics is not violated. Describe the ATP structure and the role it plays in the biochemical reaction in a cell Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved An organism’s metabolism transforms matter and energy Metabolism is the totality of an organism’s chemical reactions In a metabolic pathway, a specific molecule is altered in a series of steps to produce a product Each step is catalyzed by a specific enzyme, a macromolecule that speeds up a specific reaction Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Metabolic Pathways Catabolic pathways release energy by breaking down complex molecules into simpler compounds – Cellular respiration Anabolic pathways consume energy to build complex molecules from simpler ones – Synthesis of protein from amino acids Catabolic pathways are described as “downhill” reactions, whereas anabolic pathways are “uphill” Living things use energy released from the downhill reactions of catabolic pathways to power the uphill reactions of anabolic pathways Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Forms of Energy Energy, the capacity to cause change, can be used to do work—move matter against opposing forces, such as gravity and friction Energy exists in various forms Living cells must transform energy from one form to another to do the work of life Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Forms of Energy Kinetic energy is energy associated with motion Moving objects perform work by imparting motion to other matter – Water gushing through a dam turns turbines POTENTIAL Energy of position Thermal energy is the kinetic energy associated with random movement of atoms or molecules Thermal energy in transfer from one object to another is called heat Light is another type of energy that can be harnessed to do work, such as KINETIC photosynthesis Energy of motion Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Forms of Energy Potential energy is energy that matter possesses because of its location or structure – Water behind a dam possesses energy because of its altitude above sea level – Molecules possess energy due to POTENTIAL the arrangement of electrons in Energy of position bonds between their atoms Chemical energy is potential energy available for release in a chemical reaction Complex molecules, such as glucose, are high in chemical energy because energy is released as they are broken KINETIC down to simpler products Energy of motion Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Transformations between potential energy and kinetic energy Thermodynamics is the study of energy transformations in a collection of matter Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved The First Law of Thermodynamics According to the first law of thermodynamics, the energy of the universe is constant – Energy can be transferred and transformed, but it cannot be created or destroyed The first law is also called the principle of conservation of energy Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved The Second Law of Thermodynamics During every energy transfer or transformation, some energy is converted to thermal energy and lost as heat, becoming unavailable to do work According to the second law of thermodynamics, – Every energy transfer or transformation increases the entropy of the universe – Entropy is a measure of molecular disorder, or randomness Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved The two laws of thermodynamics Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved  1. Which process is spontaneous (happens “on its own”), the one indicated by the blue or the red arrow? 2. Make two observations about the spontaneous process regarding: — The role of energy — The change in the degree of order of the system Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved The Second Law of Thermodynamics Processes that increase the entropy of the universe can occur spontaneously Spontaneous processes occur without energy input; they can happen quickly or slowly Processes that decrease entropy are nonspontaneous; they require an input of energy Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Order is a characteristic of life Cells create ordered structures from less organized starting materials – For example, simple molecules are ordered into amino acids, which are assembled into ordered polypeptides Complex, ordered structures are also produced from simpler starting materials at the organismal level Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Do Living Organisms Violate the Second Law of Thermodynamics? Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved The Laws of Energy Transformation An isolated system, such as the liquid in a thermos bottle, is unable to exchange energy or matter with its surroundings In an open system, energy and matter can be transferred between the system and its surroundings Organisms are open systems; they absorb energy from light or food and release heat and metabolic wastes, such as CO , to the surroundings 2 Closed Open system system Energy exchange Surroundings Surroundings Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved  Living Organisms are Open Systems “Life” involves increase in the order of the system. This localized increase in order can only be achieved by receiving the energy from the surroundings. Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Living Organisms are Open Systems Heat is released to offset the increased order within living systems by increasing the disorder in the rest of the universe according to the Second Law of Thermodynamics. Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Biological Order and Disorder The evolution of complex organisms from simpler ancestors does not violate the second law Entropy (disorder) may decrease in a particular system, such as an organism, as long as the total entropy of the system and surroundings increases Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Total Energy of a System Enthalpy (H): the total potential energy of a system has two components: 1. Free energy (G) : the amount of energy available to do work and 2. Entropy (S): measure of disorder of a system; H = G + TS S G Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved  Changes in Free Energy When a system goes through a process, the enthalpy, free energy and entropy change. This change can be described by an equation: ΔH=ΔG+TΔS The rearranged equation can be used to predict whether a particular Spontaneous!!! chemical reaction will release energy or require an input of energy: ΔG=ΔH−TΔS glucose-6-phosphate → fructose-6-phosphate Biologists are interested in Δ G Spontaneous ??? because they want to know the direction of a process. Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Free-Energy Change, G Delta G Gibbs free energy, G, can be simplified and referred to as free energy Free energy is the portion of a system’s energy that can do work when temperature and pressure are uniform throughout the system, as in a living cell Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Free-Energy Change, G Delta G Change in free energy during a reaction is related to temperature and changes in enthalpy and entropy ΔG = ΔH – TΔS – G = change in free energy – H = change in enthalpy ( total energy ) – S = change in entropy – T = Temperature in Kelvin (K) Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Free-Energy Change, G Delta G The G for a process can be used to determine whether it is spontaneous or not – G is negative for all spontaneous processes – G is zero or positive for nonspontaneous processes Every spontaneous process decreases the system’s free energy Spontaneous processes can be harnessed by the cell to perform work Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Free Energy, Stability, and Equilibrium G represents the difference between free energy of the final state and free energy of the initial state ΔG = Gfinal state – Ginitial state If a reaction has negative G the system loses free energy and becomes more stable Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Free Energy, Stability, and Equilibrium Free energy can be thought of as a measure of a system’s stability; unstable systems (higher G) tend to become more stable (lower G) – For example, a diver on a platform is less stable than when floating in the water – A drop of concentrated dye is less stable than when it is dispersed randomly through a liquid – A glucose molecule is less stable than the simpler molecules into which it can be split Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved The relationship of free energy to stability, work capacity, and spontaneous change Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Free Energy, Stability, and Equilibrium Equilibrium, the point at which forward and reverse reactions occur at the same rate, describes a state of maximum stability Systems never spontaneously move away from equilibrium A process is spontaneous and can perform work only when it is moving toward equilibrium Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Free energy changes (Delta GG) in exergonic and endergonic reactions Chemical reactions can be classified based on their free-energy changes – An exergonic reaction (“energy outward”) proceeds with a net release of free energy to the surroundings – An endergonic reaction (“energy inward”) absorbs free energy from the surroundings Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Free energy changes (Delta GG) in exergonic and endergonic reactions In exergonic reactions, the products store less free energy than the reactants Because G is negative, exergonic reactions occur spontaneously Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved  ( GG) in exergonic and Free energy changes Delta endergonic reactions In endergonic reactions, the products store more free energy than the reactants Because G is positive, endergonic reactions are non-spontaneous Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Equilibrium and work in an isolated hydroelectric system Reactions in a closed system, such as an isolated hydroelectric system, eventually reach equilibrium and can then do no work Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved  Equilibrium and work in open systems The chemical reactions of metabolism never reach equilibrium in a living cell This is one of the defining features of life Like an open hydroelectric system, cells allow materials to flow in and out The flow of materials prevents metabolic equilibrium, enabling cells to continue doing work Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved Equilibrium and work in open systems Like a multistep open hydroelectric system, a catabolic pathway in a cell releases free energy in a series of reactions – For example, in cellular respiration reactions are “pulled” in one direction because the products of each reaction are the reactants in the next step – A steady inflow of glucose and release of waste products ensures that equilibrium is never reached Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved ATP powers cellular work by coupling exergonic reactions to endergonic reactions A cell does three main kinds of work: – Chemical work—pushing endergonic reactions – Transport work—pumping substances across membranes against the direction of spontaneous movement – Mechanical work—such as beating cilia or contracting muscle cells Cells manage energy resources to do work through energy coupling, the use of an exergonic process to drive an endergonic one Most energy coupling in cells is mediated by ATP Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved  How Do Anabolic (non-spontaneous) Reaction Happen? They use coupled reactions! Two reactions taken together are exergonic: (1) X → Y ΔG = +20.9 kJ/mol (+5 kcal/mol) (2) C → D ΔG = −33.5 kJ/mol (−8 kcal/mol) Overall ΔG = −12.6 kJ/mol (−3 kcal/mol) Coupled reactions have common intermediate link: (3) X + C → I ΔG = −8.4 kJ/mol (−2 kcal/mol) I (4) I → Y + D ΔG = −4.2 kJ/mol (−1 kcal/mol) Overall ΔG = −12.6 kJ/mol (−3 kcal/mol) Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved The structure and hydrolysis of adenosine triphosphate (ATP) ATP (adenosine triphosphate) is composed of ribose (a sugar), adenine (a nitrogenous base), and three phosphate groups Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved  The structure and hydrolysis of adenosine triphosphate (ATP) (2 of 2) Energy is released from ATP when the terminal phosphate bond is broken by hydrolysis. The energy does not come directly from the phosphate bonds, but from the chemical change to a state of lower free energy in the products Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved How ATP drives chemical work: energy coupling using ATP hydrolysis Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved How ATP Provides Energy That Performs Work Cellular work (mechanical, transport, and chemical) is powered by ATP hydrolysis In the cell, energy from the exergonic hydrolysis of ATP is used to drive endergonic reactions Overall, the coupled reactions are exergonic Phosphorylation, transfer of a phosphate group from ATP to another molecule, is typically used to power endergonic reactions The recipient molecule, a phosphorylated intermediate, is more reactive (less stable, with more free energy) that the original molecule Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved How ATP drives transport and mechanical work Transport and mechanical work in the cell are also nearly always powered by ATP hydrolysis ATP hydrolysis causes a change in protein shape and binding ability Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved The ATP cycle ATP is regenerated by addition of a phosphate group to adenosine diphosphate (ADP) Free energy needed to phosphorylate ADP comes from exergonic breakdown reactions (catabolism) The shuttling of inorganic phosphate and energy is called the ATP cycle; it couples energy-yielding processes to energy-consuming ones Copyright © 2021, 2017, 2014 Pearson Education, Inc. All Rights Reserved