Chapter 6 - Chapter 6 Energy Enzymes and Metabolism What...

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Chapter 6 Energy, Enzymes, and Metabolism What Physical Principles Underlie Biological Energy Transformations? Energy is the capacity to do work Cells must acquire energy from their environment Cells cannot make energy; energy is neither created nor destroyed, but energy can be transformed There are two main types of energy: Potential energy is stored energy – in chemical bonds, concentration gradients, charge imbalance, etc. Kinetic energy is the energy of movement Kinetic energy does work that alters the state or motion of matter Metabolism is sum of all chemical reactions in an organism. Can be divided into two types of activities: Anabolic reactions link simple molecules together to make complex ones – synthesis Energy-storing reactions Catabolic reactions break down complex molecules into simpler ones – degradation Energy is released – some provide energy for anabolic reactions First Law of Thermodynamics: Energy is neither created nor destroyed When energy is converted from one form to another, the total energy before and after the conversion is the same Second Law of Thermodynamics : When energy is transformed, some becomes unavailable to do work – lost as heat No physical process or chemical reaction is 100 per cent efficient predicts that, as a result of energy conversions, disorder tends to increase In any system: Total energy = Usable energy + Unusable energy Enthalpy (H) = Free Energy (G) + Entropy (S) or H = G + TS (T = absolute temperature) G = H – TS Free energy (G) is usable energy Change in energy can be measured in calories or joules Change in free energy ( Δ G) in a reaction is the difference in free energy of the products and the reactants Δ G = Δ H – T Δ S If Δ G is negative, free energy is released (i.e. exothermic)
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If Δ G is positive, free energy is consumed (i.e. endothermic) If free energy is not available, the reaction does not occur Disorder tends to increase due to energy transformations To maintain order, life requires a constant input of energy It may seem that highly complex organisms are in apparent disagreement with the second law, but this is not the case.
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