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Unformatted text preview: Bioenergetics & Enzymes - 1 - BIOENERGETICS & ENZYMES CONCEPTS CHECK LIST INTRODUCTION An organisms metabolism refers to all the enzyme-catalyzed reactions that it performs. An organisms metabolic events can be considered as a variety of stepwise enzyme-catalyzed reactions that we refer to as pathways. The metabolic pathways occurring in an organism can be divided into two broad categories: catabolic pathways and anabolic pathways. In general, catabolic pathways are those that break down complex molecules into simpler molecules, and generally release energy for performing cellular work. In general, anabolic pathways are those that make complex molecules from simpler molecules, a form of cellular work that requires an input of energy. Catabolic pathways are generally coupled to anabolic pathways. INTRODUCTION TO THERMODYNAMICS The first law of thermodynamics tells us that that although energy can be transferred (from one thing to another) and transformed into different states (e.g. chemical or thermal), it cannot be created or destroyed (there is a finite amount of energy in the universe). The second law of thermodynamics tells us that whenever a process transfers of transforms energy, the overall process increases the randomness of the universe (and thus less of the energy in the universe is in a form available to do work). Thermodynamically, organisms are energy transformers and operate as open systems that transfer energy to and from their surroundings. Organisms can perform three types of cellular work with the energy that they gain from their surroundings: chemical work, mechanical work, and transport work. Exergonic reactions are those that result in an overall loss of free energy from the system (the products have less free energy than the reactants); in cells, some of the energy they release can be captured (usually by an energy carrier molecule) to do cellular work... the rest is lost as heat to the environment. Endergonic reactions are those that result in an overall gain in free energy for the system (the products have more free energy than the reactants); in cells, the energy they require (work!) is usually provided by energy carriers that transfer some of their energy to perform the work... the rest is lost as heat to the environment. The (overall) free energy change ( G) associated with an exergonic process is negative ( ! G). The (overall) free energy change ( G) associated with an endergonic process is positive (+ G). ATP: ADENOSINE TRIPHOSPHATE ATP is an energy carrier found in all organisms. Organisms use (some of) the energy released from the hydrolysis of its phosphoanhydride bonds to power various types of work... the rest is lost as heat to the environment....
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