Chapter 8 Energy and Enzymes PDF

Chapter 8 Energy and Enzymes: An Introduction to Metabolism  Energy and enzymes make cellular activity possible Activities change constantly in response to signals from cells Energy or environment and Enzymes dire...

Chapter 8 Energy and Enzymes: An Introduction to Metabolism  Energy and enzymes make cellular activity possible Activities change constantly in response to signals from cells Energy or environment and Enzymes direct which reactions occur and when Enzym Enzymes work to help cells es acquire and use energy Metabolic pathways: Ordered series of chemical reactions that build up or break down molecules Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved  Two types of energy 8.1 Kinetic energy—energy of What motion: Happens Thermal energy: energy of to molecules moving Energy Potential energy—energy in stored in position or Chemica configuration: Chemical energy: energy l stored in chemical bonds Reaction Energy can be transformed s? from one type to another Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 8.1 Energy Transformations Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved  Amount of potential energy in covalent bond reflects: Position of shared electrons Relative to nuclei of bonded atoms Chemical Reactions Potential energy of molecule Involve depends on configuration and Energy position of shared electrons: Transformati Longer, weaker bonds with ons equally shared electrons have high potential energy Shorter, stronger bonds with unequally shared electrons have low potential energy Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 8.2 Potential Energy in Molecules Is Based on Bonds Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved  Chemical reactions: Products formed have shorter, stronger covalent Chemical bonds than reactants Reactions Potential energy in bonds Involve decreases Energy Difference in energy Transformati transformed into equal ons amount of kinetic energy Change in energy transformed to thermal energy or light Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved  First law of thermodynamics: Energy is conserved Energy cannot be created or destroyed Chemical Energy can only be Reactions transferred and transformed Involve Enthalpy (H)—total energy in a Energy Transformati molecule: ons Includes potential energy in bonds of molecule Plus the effect of molecule’s kinetic energy on surrounding pressure and volume Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Chemical Reactions Involve Energy Transformations Changes in enthalpy are primarily based on difference in potential energy Exothermic reactions: Reactions release heat Products have less potential energy than reactants Endothermic reactions: Heat energy is taken up during reaction Products have higher potential energy than reactants Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Chemical Reactions Involve Energy Transformations Entropy (S)—amount of disorder: Another factor that changes during chemical reaction When products of chemical reaction become less ordered than reactant molecules: Entropy increases Second law of thermodynamics—total entropy always increases in a system Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 8.3 When a Reaction Generates More Disorder, Entropy Increases Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved  Even if reaction is spontaneous, it may not happen quickly: For most reactions to proceed: One or more chemical Temperatu bonds have to break re and Others have to form Concentrat Substances must collide in ion Affect specific orientation to Reaction brings electrons involved near each other Rates Higher concentrations increase number of collisions Higher temperature therefore increase reaction rate Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved  Reduction–oxidation reactions (redox reactions): Chemical reactions that Redox involve electron transfer: Reaction Oxidation: loss of an s electron(s) Transfer Reduction: gain of an electron(s) Energy Always occur together via Represent energetic Electrons coupling of two half- reactions: Oxidation is exergonic Reduction is endergonic Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Web Activity: Redox Reactions Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Redox Reactions Transfer Energy via Electrons During redox reactions, electrons may be gained or lost in two ways: Change in number of electrons in valence shell of atom Electrons transferred as new covalent bonds formed with other atoms: Atom is reduced or oxidized Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Another Approach to Understanding Redox Electrons can be transferred from electron donor to electron acceptor Most electron acceptors gain potential energy as they are reduced Electrons are usually accompanied by a proton. H+ Reduction often “adds H`s” Oxidation often “removes H’s” Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved  Another Approach to Understanding Redox Flavin adenine dinucleotide (FAD) accepts two electrons electrons plus two protons to form FADH2 : Electron carrier—has “reducing power” Nicotinamide adenine dinucleotide NDA   accepts two electrons plus one proton to form NADH: Electron carrier These electron carriers readily donate electrons to other molecules Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved A T P Transfers Energy via Phosphate Groups Adenosine triphosphate (A T P)— energy currency for cells: Provides fuel for most cellular activities Ribonucleotide used for R N A synthesis A T P has a great deal of potential energy: Forms bonds between three negatively charged phosphate groups Negative charges repel each other Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 8.8 Adenosine Triphosphate (A T P) Stores a Large Amount of Potential Energy Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 8.9 Energy Is Released When A T P is Hydrolyzed Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved 8.3 How Enzymes Work Activation Transition energy: Kinetic energy Required to strain chemical state: Intermediate point between breaking old bonds and forming bonds in molecules to prevent new ones reaction and formation of Free energy of transition state is product high Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 8.11 Changes in Free Energy during a Chemical Reaction Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Enzymes Help Reactions Clear Two Hurdles Before reaction can take place, reactants need to: Collide in precise orientation Have enough kinetic energy to overcome activation energy barrier and achieve transition state Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Enzymes Bring Substrates Together Bring reactants together in precise orientations Enzymes are Make reactions more likely catalysts: Are specific for single type of reaction When reactants undergo chemical reaction by binding to an enzyme, they are substrates Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Enzymes Bring Substrates Together Substrates bind to enzyme’s active site: Active-site binding helps substrates collide in precise orientation Bonds break and form to generate products Many enzymes undergo conformational change: When substrates are bound to active site, this change is called an induced fit Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Enzymes Lower the Activation Energy Substrates enter active site—are held in place: By hydrogen bonding By weak interactions with amino acid residues in active site Interaction between substrate and enzyme increases Enzymes decrease Bonds in substrate activation are destabilized to form energy transitionrequired state for reaction to proceed Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 8.13 An Enzyme Changes the Activation Energy of a Reaction Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 8.14 A Three-Step Process to Model Enzyme Action Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Figure 8.15 Enzyme- Catalyzed Reactions Can Be Saturate d Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Do Enzymes Work Alone? Molecules that are not part of enzyme are required for enzyme functionality: 1. Cofactors—inorganic ions, such as Zn2 , Mg2 , and Fe 2 that reversibly interact with enzymes 2. Coenzymes—organic molecules, such as NADH or FADH2 , that interact with enzymes 3. Prosthetic groups—non-amino acid atoms or molecules permanently attached to proteins Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved 8.4 What Factors Affect Enzyme Function? Enzyme’s structure critical to its function: Sensitive to alteration of protein shape Activity of enzyme changes due to: Temperature pH Interactions with other molecules Modifications of primary structure Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Enzymes Are Optimized for Particular Environments Temperature: Affects folding and movement of enzyme and substrates Affects kinetic energy p H: Affects enzyme’s shape and reactivity Affects charge on acidic and basic groups Both temperature and p H affect enzyme shape and reactivity Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved 8.5 Enzymes Can Work Together in Metabolic Pathways Metabolic pathways: Series of reactions Each catalyzed by different enzyme Build biological molecules Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved Metabolic Pathways Are Regulated Occurs when enzyme in pathway is Feedback inhibited inhibition: Inhibition is by final product of pathway As It “feeds back” to stop reaction concentration Amount of initial substrate is not of product depleted becomes Stored or used for other reactions abundant: Copyright © 2020, 2017, 2014 Pearson Education, Inc. All Rights Reserved