03BiochemEnergetics - Ch.3,pp.8388,93100 Energy ;...

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Biochemical Energetics I Ch. 3, pp. 83-88, 93-100. Energy I told you last time that cells obey the laws of chemistry; they also obey the laws of physics. The first law of thermodynamics is that energy cannot be created or destroyed, just converted from one form to another. We will begin by considering the forms of energy that are important in biological processes. Potential energy Potential energy is stored energy. Energy is stored in covalent bonds between atoms in a molecule, and can be released when the bonds are broken. This energy is called enthalpy . (Energy is also stored in differences in electric charge or differences in concentrations of ions or molecules across membranes, as we shall see later.) Kinetic energy Kinetic energy derives from movement. The radiant energy of sunlight is the kinetic energy of photons or light waves from the sun. Heat, or thermal, energy is the energy of molecules in motion. Interconversion of energy Most of the energy in the living world comes from sunlight. Plants convert the kinetic energy of sunlight into potential energy in the bonds of sugars and starch (in the process some energy is lost as heat). Some animals obtain this potential energy by eating plants, and others by eating animals lower on the food chain. The potential energy in food molecules is released as they are broken down in the process of catabolism . Later in the course we will look in detail at the catabolism of a common six-carbon sugar, glucose . Glucose catabolism is used in most cell types to generate energy carrier molecules such as adenosine triphosphate (ATP). Some of the energy stored in carrier molecules is converted by anabolic reactions into potential energy in complex molecules the cell needs to live and grow (again with some loss as heat). Potential energy in energy carriers can also be converted into kinetic energy when an organism moves. (The sum of the reactions in a cell or organism, including catabolism and anabolism, constitute its
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This note was uploaded on 02/02/2009 for the course PHYS 10a taught by Professor Martens during the Spring '07 term at Brandeis.

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03BiochemEnergetics - Ch.3,pp.8388,93100 Energy ;...

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