Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 Chapter 8 Metabolism: Energy, Enzymes, and Regulation

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2 An Overview of Metabolism metabolism is the total of all chemical reactions in the cell and is divided into two parts –catabolism – the energy-conserving reactions –anabolism – the synthesis of complex organic molecules from simpler ones

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 3 Anabolism requires energy –transferred from energy source to the synthetic systems of the cell by ATP also requires a source of electrons stored in the form of reducing power

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4 Overview of Metabolism Figure 8.1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5 The processes used by organisms to obtain energy and to do chemical work are the basis of the functioning of ecosystems. Figure 8.2

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 6 Energy and Work energy –capacity to do work or to cause particular changes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 7 Types of work carried out by organisms chemical work –synthesis of complex molecules transport work –take up of nutrients, elimination of wastes, and maintenance of ion balances mechanical work –Cell motility and movement of structures within cells

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8 The Laws of Thermodynamics thermodynamics –a science that analyzes energy changes in a collection of matter called a system (e.g., a cell) –all other matter in the universe is called the surroundings

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9 Energy units calorie (cal) –amount of heat energy needed to raise 1 gram of water from 14.5 to 15.5°C joules (J) –units of work capable of being done by a unit of energy –1 cal of heat is equivalent to J of work

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 10 First law of thermodynamics energy can be neither created nor destroyed total energy in universe remains constant –however energy may be redistributed either within a system or between the system and its surroundings

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 11 Second law of thermodynamics entropy –amount of disorder in a system physical and chemical processes proceed in such a way that the disorder of the universe increases to the maximum possible

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 12 Second law in action… molecules are redistributed, increasing entropy of system Figure 8.3

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13 Free Energy and Reactions  G =  H - T  S expresses the change in energy that can occur in chemical reactions and other processes used to indicate if a reaction will proceed spontaneously

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14  G =  H - T  S  G –free energy change –amount of energy that is available to do work  H –change in enthalpy (heat content) T –temperature in Kelvin  S –change in entropy

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 15 Chemical equilibrium equilibrium consider the chemical reaction A + B C + D –reaction is at equilibrium when rate of forward reaction = rate of reverse reaction equilibrium constant (K eq ) –expresses the equilibrium concentrations of products and reactants to one another

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16 Standard free energy change (  G o ) free energy change defined at standard conditions of concentration, pressure, temperature, and pH  G o ´ –standard free energy change at pH 7 –directly related to K eq  G o ´ = RTlogK eq

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17 The relationship… Exergonic reactions A+BC+D Keq >1  G o ´ is negative (reaction proceeds spontaneously) Endergonic reactions A+BC+D Keq < 1  G o ´ is positive (reaction will not proceed spontaneously) Figure 8.4

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 18 Adenosine 5’-triphosphate (ATP) Energy Currency of the Cell Figure 8.5

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 19 Role of ATP in Metabolism exergonic breakdown of ATP is coupled with endergonic reactions to make them more favorable Figure 8.6

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 20 The cell’s energy cycle Figure 8.7

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21 Oxidation-Reduction Reactions and Electron Carriers many metabolic processes involve oxidation-reduction reactions (electron transfers) electron carriers are often used to transfer electrons from an electron donor to an electron acceptor

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 22 Oxidation-Reduction (Redox) Reactions transfer of electrons from a donor to an acceptor can result in energy release, which can be conserved and used to form ATP

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 23 Oxidation and Reduction Reactions Oxidation-reduction (redox) reactions involve the transfer of electrons. These reactions always occur simultaneously because an electron gained by one molecule is donated by another molecule. Remember as OiL RiG; OiL= oxidation involves loss; RiG= reduction involves gain.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24 ATP Production and Energy Storage Energy from the chemical bonds of nutrients is concentrated in the high-energy phosphate bonds of ATP. Substrate-level phosphorylation describes the transfer of phosphate from a phosphorylated organic nutrient to ADP to form ATP. Oxidative phosphorylation phosphorylates ADP using inorganic phosphate and energy from respiration. Photophosphorylation is the phosphorylation of ADP with inorganic phosphate using energy from light. There is a cyclical conversion of ATP from ADP and back with the gain and loss of phosphate

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 25 Standard Reduction Potential (E 0 ) equilibrium constant for an oxidation-reduction reaction a measure of the tendency of the reducing agent to lose electrons more negative E 0  better electron donor more positive E 0  better electron acceptor

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 26 Table 8.1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 27 The greater the difference between the E 0 of the donor and the E 0 of the acceptor  the more negative the  G o ´ Figure 8.8

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 28 Electron Transport Systems (ETS) electron carriers organized into ETS with the first electron carrier having the most negative E’o –as a result the potential energy stored in first redox couple is released and used to form ATP

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 29 Electron Transport Systems Figure 8.9

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 30 Electron carriers NAD –nicotinamide adenine dinucleotide NADP –nicotinamide adenine dinucleotide phosphate Figure 8.10 (a)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 31 Figure 8.10 (b)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 32 Figure 8.10 (c)

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 33 Electron carriers FAD –flavin adenine dinucleotide FMN –flavin mononucleotide –riboflavin phosphate Figure 8.11 riboflavin

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 34 Electron carriers coenzyme Q (CoQ) –a quinone –also called ubiquinone Figure 8.12

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 35 Electron carriers cytochromes –use iron to transfer electrons iron is part of a heme group Figure 8.13

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 36 Electron carriers nonheme iron proteins –e.g., ferrodoxin –use iron to transport electrons iron is not part of a heme group

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 37 Enzymes protein catalysts –have great specificity for the reaction catalyzed and the molecules acted on catalyst –substance that increases the rate of a reaction without being permanently altered substrates –reacting molecules products –substances formed by reaction