SC BIOL 110 - 5, The Working Cell (26 pages)

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Forms of Energy Energy is the capacity to cause change It exists in various forms Kinetic energy is energy associated with motion Heat thermal energy is kinetic energy associated with random movement of atoms or molecules Potential energy is energy that matter possesses because of its location or structure Chemical energy is potential energy available for release in a chemical reaction Energy can be converted from one form to another Thermodynamics is the study of energy transformations ATP powers cellular work by coupling exergonic reactions to endergonic reactions ATP adenosine triphosphate is the cell s energy shuttle The bonds between the phosphate groups of ATP s tail can be broken by hydrolysis Energy is released from ATP when the terminal phosphate bond is broken Fig 8 8 ATP is composed of ribose a sugar adenine a nitrogenous base and three phosphate groups Adenine Phosphate groups Ribose Fig 8 12 The Regeneration of ATP ATP is a renewable resource that is regenerated by addition of a phosphate group to adenosine diphosphate ADP ATP H2O Energy from catabolism exergonic energy releasing processes ADP P i Energy for cellular work endergonic energy consuming processes The energy to phosphorylate ADP comes from catabolic reactions in the cell Enzymes speed up metabolic reactions by lowering energy barriers A enzyme is a catalyst that speeds up a reaction without being consumed by the reaction Every chemical reaction between molecules involves bond breaking and bond forming The initial energy needed to start a chemical reaction is called the free energy of activation or activation energy EA For a reaction to happen the reactants must overcome the EA barrier Activation energy is often supplied in the form of heat from the surroundings Fig 8 14 A B C D Free energy Transition state A B C D EA Reactants A B G O C D Products Progress of the reaction Enzymes Lower the EA Barrier Enzymes catalyze reactions by lowering the EA barrier Enzymes do not affect the change in