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Chapter 4

BIOL 1000 Chapter 4 - Energy and Enzymes.docx

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York University
BIOL 1000
Jennifer Steeves

4.1 – Energy and the Laws of Thermodynamics • Energy – The capacity to do work • Kinetic Energy – the energy of motion • Potential Energy – Energy stored in an object because of its location or chemical structure • Energy may be readily converted between potential and kinetic states  It cannot be created or destroyed Thermodynamics • The study of energy flow between a system and its surroundings during chemical and physical reactions • Isolated System – A system that does not exchange energy or matter with its surroundings • Closed System – A system that exchanges energy but not matter with its surroundings • Open System – A system that exchanges both energy and matter with its surroundings • First Law – The total amount of energy in a system and its surroundings remains constant • Second Law – In any process involving a spontaneous change from an initial to a final state, the total entropy of the system and its surroundings always increases • Life obeys the Second Law of Thermodynamics • Life is maintained in a highly ordered state because it is an open system  Bringing energy in from the surroundings and in turn increasing the disorder of the surroundings – unusable energy released, as heat, to the surroundings 4.1 – Free Energy and Spontaneous Reactions • Spontaneous Reaction – A reaction that will occur without the input of energy from the surroundings  Releases Free Energy – energy that is available to do work • The Change in Free Energy (ΔG) is influenced by two factors  The Change in Enthalpy (ΔH) – Potential energy in a system  The Change in Entropy (ΔS) of the system as a reaction goes to completion • ΔG = ΔH – TΔS is the Free Energy Equation • Relative concentrations of reactants and products oppose the completion of spontaneous reactions • These, and other such factors, produce an equilibrium point at which reactants are converted to products and vice versa at equal rates. • Organisms reach equilibrium (ΔG=0) only when they die • Exergonic Reactions – Reactions with a negative ΔG are spontaneous; they release free energy • Endergonic Reactions – Reactions with a positive ΔG require free energy • Metabolism – The biochemical modification and use of energy in the synthesis and breakdown of organic molecules • Catabolic Pathway – releases the potential energy of a molecule by breaking it down to a simpler molecule • Anabolic (Biosynthetic) Pathway – Uses energy to convert a simple molecule to a more complex molecule (ΔG) 4.3 – ATP Is the Energy Currency of the Cell • The hydrolysis of ATP release free energy that can be used as a source of energy for the cell • A cell can couple the exergonic reaction of ATP b
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