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# lec5 note - LECTURE 5 01 September 2010(Peter J Hollenbeck...

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-1- LECTURE 5. 01 September 2010 (Peter J. Hollenbeck) BIOL 231 ENERGETICS & THERMODYNAMICS IN THE CELL Read: Chap 3: 81-98; 104-14; panel 3-1; Problems: 14-17; see Q3-14, Q3-17 in ECB (your text) I. Energy in Chemical Reactions A. Equilibrium & Disequilibrium (1) Equilibrium is defined as the lowest energy state for a system or reaction. Any reaction, such as: A + B <=> C + D will proceed spontaneously to an equilibrium state, at which there will be a characteristic ratio of products to reactants, regardless of the concentrations, absolute or relative, at which they start out. So, for the reaction above, at equilibrium, the ratio eq [C][D]/[A][B] is equal to a constant, called K. We will return to this shortly. (2) Living systems, such as cells, are in a state of DISEQUILIBRIUM with their environment, and require a constant input of energy to maintain themselves in this state. A cell at equilibrium is dead, dead, dead. (3) We can measure the energy stored in a chemical disequilibrium: the farther we are from equilibrium, the more potential energy is contained there. Cells use energy to create various disequilibria and then use the energy stored there to perform useful work. To understand this, we first need to review a little bit of thermodynamics. ... QUESTIONS: ***In WHAT DIRECTION will events proceed in the cell? ***Do particular reactions CONSUME or PRODUCE energy? B. First Law of Thermodynamics - energy is neither created nor destroyed, but can change forms. (1) The cell can be thought of as a machine that converts energy from one form to another. Photosynthetic cells (e.g., in plants) convert the energy of sunlight into chemical energy. All cells convert one form of chemical energy to another, and convert chemical energy into heat and mechanical energy. (2) For the cell, the pathway for energy conversion is critical! You can use a flame to 61 26 2 2 burn glucose (C H O ) to yield CO and H O, releasing the energy of chemical bonds 22 as heat and light. But when a cell “burns” glucose, also yielding CO and H O, it uses

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lec5 note - LECTURE 5 01 September 2010(Peter J Hollenbeck...

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