CHAPTER 9 CELLULAR RESPIRATION

CHAPTER 9 CELLULAR RESPIRATION - CHAPTER 9 CELLULAR...

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CHAPTER 9 CELLULAR RESPIRATION: HARVESTING CHEMICAL ENERGY I. Principles of Energy Conservation As open systems, cells require outside energy sources to perform cellular work (e.g., chemical reactions, transport of materials, and mechanical movement). Energy flows into most ecosystems as sunlight. Photosynthetic organisms trap a portion of the light energy and transform it into chemical bond energy of organic molecules. O2 is released as a by product. Cells use some of the chemical bond energy in organic molecules to make ATP (the energy source for cellular work). The rest of the energy leaves living organisms as heat. Chemical elements essential for life are recycled, but energy is not. Thus organisms need a constant supply of energy. How do cells obtain chemical energy? The answer is cellular respiration. A. Cellular respiration and fermentation are catabolic (energy-yielding) pathways Fermentation = - Is an anaerobic process - Results in a partial degradation of sugars Cellular respiration = - Most prevalent and efficient catabolic pathway - Is an exergonic process. -Can be summarized as:
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- Carbohydrates, proteins, and fats can all be metabolized as fuel, but cellular respiration is most often described as the oxidation of glucose: B. Cells recycle the ATP they use for work The catabolic process of cellular respiration transfers the energy stored in food molecules to ATP. ATP (adenosine triphosphate) = Nucleotide with high energy phosphate bonds that the cell hydrolyzes for energy to drive endergonic reactions. - The cell taps energy stored in ATP by enzymatically transferring terminal phosphate groups from ATP to other compounds. (Recall that direct hydrolysis of ATP would release energy as heat, a form unavailable for cellular work.) - The compound receiving the phosphate group from ATP is said to be phosphorylated and becomes more reactive in the process. - The phosphorylated compound loses its phosphate group as cellular work is performed; inorganic phosphate and ADP are formed in the process. - Cells must replenish the ATP supply to continue cellular work. Cellular respiration provides the energy to regenerate ATP from ADP and inorganic phosphate. C. Redox reactions release energy when electrons move closer to electronegative atoms 1. An introduction to redox reactions Oxidation-reduction reactions = Chemical reactions which involve a partial or complete transfer of electrons from one reactant to another; called redox reactions for short. Oxidation = Reduction = Generalized redox reaction:
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Electron transfer requires both a donor and acceptor, so when one reactant is oxidized the other is reduced. Not all redox reactions involve a complete transfer of electrons, but, instead, may just change the degree of sharing in covalent bonds. - Since electrons lose potential energy when they shift toward more
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This note was uploaded on 03/18/2008 for the course BS 110 taught by Professor S.lawrence during the Spring '07 term at Michigan State University.

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CHAPTER 9 CELLULAR RESPIRATION - CHAPTER 9 CELLULAR...

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