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Energy and Metabolism “life = energy transformation” Each property by which we define life (order, growth, repro, responsiveness, internal regulation) requires ENERGY Deprived of a source of energy, life stops Energy flow on Earth Energy flows into our biosphere from the sun, a small portion of which is captured by plants, algae, and certain PS bacteria Energy exits the biosphere as HEAT The flow of energy in living systems Thermodynamics = branch of chemistry concerned with energy changes Energy = capacity to do work Energy exists in 2 states: kinetic energy potential energy Energy may take many forms: mechanical, sound, light, electrical, heat Fig. 6.1 Potential energy and kinetic energy The energy required for the girl to climb the stairs is stored as potential energy; the stored energy is released as kinetic energy as the girl slides down There are millions of biological examples of potential/kinetic energy Identify several: The most convenient measure of energy is heat • Heat capacity (energy content) of biomolecules (sugars, proteins, lipids) is expressed in Calories (cal) • The term ‘Joule’ is used in Physics (= 0.239 cal) • The chemical calorie is different than our dietary “Calorie” (which is actually a Kcal!) Photosynthesis is a wonderful provider! • A simple sugar (glucose, fructose, etc.) provides ~700 kcal or energy per mole! • Photosynthate sugars provide the C skeleton to make: » Amino acids for proteins » Fatty acid chains and glycerol for lipids • One mole of lipid (with three 16-C saturated fatty acid chains) yields 2340 kcal!! Without constant inflow of solar energy, life as we know it, would not exist The Laws of Thermodynamics • A set of 2 universal laws govern all energy changes in our Universe – The First Law of Td: Energy cannot be created or destroyed; it can only change from one form to another – The Second Law of Td: Concerns energy transformations – in every transformation, some “useable” energy is lost. Disorder (entropy) constantly increases in the Universe Free Energy within cells (Gibbs Free Energy) G = H – TS Where: G = energy available within a molecule or molecules entering a rxn H = the energy contained in all the bonds of the molecule(s) T = temperature in °Kelvin (°C + 273) S = energy unavailable due to Entropy Chemical rxns and Free Energy ΔG = ΔH – TΔS The change in Free Energy of a chemical rxn is equal to the change in total bond energy minus Temperature times the change in entropy (order) ΔG is >0 for endergonic rxns, <0 for exergonic rxns Fig. 6.4 Fig. 6.6 ATP: The energy currency of the cell Fig. 6.7 ATP cycles continuously Enzymes and cellular reactions • Enzymes aid in bringing together reactants or binding a substrate so that key bonds are broken or formed Characteristics of enzymes: – Proteins (mostly) – Not altered by the reaction they produce; recyclable – Specific for the substrate(s) to which they bind – Lower the energy of activation for a rxn Model of enzyme activity Re: enzymes are re-useable!! RE: Factors affecting enzyme activity • Heat and pH • Substrate concentration • Enzyme inhibition: • Competitive inhibition • Non-competitive inhibition • Biofeedback inhibition Biofeedback inhibition Article Review #3 Schrezenmeir, J. and M. deVrese. 2001. Probiotics, prebiotics, and synbiotics – approaching a definition. Am. J Clin. Nutr. 73: 361-364. Chandel, N.S. et al. 1997. Cellular respiration during hypoxia. J. Biological Chemistry. 272: 18808-18815. Amerine, M.A. and R.E. Kunkee. 1968. Microbiology of winemaking. Ann. Rev. Microbiol. 22: 324-339. Hibberd, J.M. and W.P. Quick. 2002. Characteristics of C4 photosynthesis in stems and petioles of C3 flowering plants. Nature. 415: 451-455.