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Chapter 4

Chapter 4 - Energy and Enzymes Summary Notes Complete summary of chapter 4, including all topics covered in lecture in depth, with definitions, and explanations. Cuts all the excess fluff in the textbook, straight to the point biology

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Diane Williams

BI110 CHAPTER 4 ENERGY AND ENZYMES 4.1 Energy and the Laws of Thermodynamics • Energy can be defined as the capacity to do work 4.1a Energy Exists in Different Forms and States • energy can exist in many different forms, including heat, chemical, electrical, mechanical energy and electromagnetic radiation (visible, infrared and ultraviolet light) • Kinetic energy is the energy possessed by an object because it is in motion • Potential energy is stored energy; the energy of an object because of its location or chemical structure 4.1b The Laws of Thermodynamics Describe the Energy Flow in Natural Systems • Thermodynamics is the study of energy and its transformations • An isolated system is one that does not exchange matter or energy with it’s surroundings (ie. thermos bottle) a closed system can exchange energy but not matter with its surroundings (ie. Earth) • • an open system can exchange energy and matter freely between the system and the surroundings (ie. living organisms) 4.1c The First Law of Thermodynamics • first law of thermodynamics, energy can be transformed from one form into another or transferred fro one place to another, but it cannot be created or destroyed (AKA Principle of the Conservations of Energy) 4.1d The Second Law of Thermodynamics • each time energy is transformed from one form into another, some of the energy is lost and unavailable to do work, it is never 100% efficient • entropy is the disorder or randomness of the universe, increased by the inefficient energy lost in transitions • second law of thermodynamics states that the total disorder (entropy) of a system and its surroundings always increases • systems will move spontaneously toward arrangements with greater entropy 4.1e Life and the Second Law of Thermodynamics • it takes energy to maintain low entropy • living things bring in energy and matter and use them to generate order out of disorder 4.2 Free Energy and Spontaneous Reactions • spontaneous reactions are chemical reactions that will occur without the input of energy, means only that it will occur, not necessarily a fast reaction BI110 4.2a Energy Content and Entropy Contribute to Making a Reaction Spontaneous 1. Reactions tend to be spontaneous if the products have less potential energy than the reactants enthalpy is the amount of potential energy in a system (H) • • endothermic reactions absorb energy, those that release energy are exothermic 2. Reactions tend to be spontaneous when the products are less ordered than the reactants • entropy (free energy) of the products is greater than the entropy of the reactants. High potential energy, low disorder --> low potential energy, high disorder 4.2b The Change in Free Energy Indicates Whether a Reaction is Spontaneous • free energy is the portion of a system’s energy that is available to do work (G) • In living organisms, free energy accomplishes the chemical and physical work involved in activities such as the synthesis of molecules, movement and reproduction • Change in free energy: ΔG = ΔH -TΔS • Δfree energy = Δenthalpy - (absolute temp)(Δchange in entropy) • where ΔH is the change in enthalpy, ΔS is the change in the entropy of the system of the course of the reaction and T is the absolute temperature in kelvin the equation says that the free energy change as a system goes from initial to final states is the sum • of the changes in energy content and entropy • For a reaction to be spontaneous, the ΔG must be negative • for all chemical and physical processes, there is an interplay of both entropy and enthalpy to determine whether it will occur spontaneously • ΔG represents the difference between the free energy of the final state compared with the initial state and thus -ΔG indicates that the products have less free energy than the reactants • high free energy = less stable, thus wants to be more stable 4.2c Life and Equilibrium • equilibrium is another term for maximum stablility • point of chemical equilibrium is a state in which the reaction does not stop but rather a state in which the rate of forward reaction equals the rate of backwards reaction. NOT NECESSARILY EVEN!! • lowest point and max stability at equilibrium, NO free energy (ΔG is 0) to move away from the equilibrium point requires free energy and thus will not be spontaneous • • the ΔG of life is always negative as organisms constantly take in energy-rich molecules and use them to do work • organisms reach equilibrium (ΔG = 0) only when they die 4.2d Metabolic Pathways Consist of Exergonic and Endergonic Reactions BI110 • exergonic reactions release free energy (negative ΔG) • endergonic reactions store free energy, more free energy than reactants (positive ΔG) • metabolic pathways are a series of sequential reactions in which the products of one reaction are used immediately as the reactants for the next reaction in the series • catabolic pathways are metabolic pathways in which energy is released by the break-down of complex molecules to simpler compounds • anabolic pathways are metabolic pathways in which energy is consumed to build complicated molecules from simpler ones; often called biosynthetic pathways Summary Table of Life -ΔG ΔG = 0 +ΔG ENERGY: PROD < REACTANTS ENERGY: PROD > REACTANTS Exergonic Endergonic Exothermic Endothermic EQUILIBRIUM Catabolic Anabolic / Biosynthetic SPONTANEOUS NEEDS FREE ENERGY 4.3 The Energy Currency of the Cell: ATP 4.3a ATP Hydrolysis Releases Free Energy • ATP consists of a five-carbon sugar, ribose, linked to the nitrogeneous base adenine and a chain of three phosphate groups. It possess what are called high-energy phosphate bonds • each of the phosphate groups is closely associated with each other and their negative charges strongly repel each other • removal of one or two of the three phosphate groups is a spontaneous reaction that relieves the repulsion and releases large amounts of free energy (a hydrolysis reaction) 4.3b ATP and Energy Coupling • if most ATP was hydrolyzed in isolation, it would be very difficult for the cell to trap the heat produced and use it to do work, in ad
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