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| Unit 3: Demos |
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Enzymes The Active Site of Carboxypetidase (for more see below) Chemiosmosis Video Chemiosmosis Video Why do our muscles hurt after exercise? (optional) ATP challenge: 6-carbon fatty acid vs. glucose Endothermic v. ectothermic Temperature, size, and metabolic
rate More on carboxypeptidase 1,
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Energy Changes in Endergonic Reactions Endergonic reactions are those reactions whose products have more energy than the reactants and therefore require a net input of energy to go "uphill" from the initial state to the final state. Like exergonic reactions, endergonic reactions require an additional input of energy, the activation energy, to get the reaction started. Once the activated state has been achieved, the reactants form a temporary complex with the enzyme, the enzyme substrate-complex, which breaks down to yield the end products of the reaction plus an amount of free energy equal to the activation energy. Whether we are talking about an endergonic or exergonic reaction, the amount of activation energy necessary to initiate the reaction is much less in the presence of a catalyst than in its absence. It is this lowering of the activation-energy barrier by enzymes that make possible most of the chemical reactions of life. Note that the amount of free energy liberated by the reaction is unchanged by the catalyst--it is the same for both the catalyzed and the uncatalyzed reaction, and only the amount of activation energy required is changed.
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