北京大学.生物化学.2005 (2).ppt

Chapter 13 Principles of BioenergeticsBioenergetics : the quantitative study of energy transductions in living cells and the physical-chemical nature underlying these processes. Cells need energy to do all their work To generate and maintain its highly ordered structure (biosynthesis of macromolecules). To generate motion (mechanical work). To generate concentration and electrical gradients across cell membranes (active transport). To generate heat and light. The “energy industry”(production, storage and use) is central to the economy of the cell society! Cells have to use chemical energy to do all their work Living cells are generally held at constant temperature and pressure: chemical energy (free energy, ?G) has to be used by living organisms. Biological energy transformation obey the two basic laws of thermodynamics. The free energy concept of thermodynamic is more important to biochemists than to chemists Thermodynamic quantities describe energy changes occurring in a chemical reaction ?G = ?Go + RT ln Q (Q = [products]/[reactants]) ?G o = -RT ln Keq (Keq : equilibrium constant) The actual free energy change (?G ) determines whether a reaction occurs spontaneously. The standard free energy change in biochemistry (?Go) is a constant (measured under a standard set of conditions). ?G for a reaction can be larger, smaller, or the same as ?Go, depending on the concentrations of the reactants and products (Q: mass action ratio). The ?G and ?Go values are additive when reactions are coupled, thus a thermodynamically unfavorable reaction can be driven by a favorable one. The overall K`eq is multiplicative (the product of two,两值相乘), although ?Go is additive (the algebraic sum of two，两值相加). Note: the rate of a chemical reaction has nothing to do with its ?G or ?Go, but is determined by its activation energy (?G ?)! ATP is the universal currency for biological energy This was first perceived by Fritz Lipmann and Herman Kalckar in 1941 when studying gl