midterm 2 - Chapter 7: Pathways that harvest chemical...

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Chapter 7: Pathways that harvest chemical energy I. How does glucose oxidation release chemical energy? i. Most common fuel, sugar glucose ii. Use fats and proteins to, but they must be converted to intermediate compounds in the various pathways of glucose metabolism. iii. Several principles that govern metabolic pathways 1. Complex chemical transformations in the cell occur in a series of separate reactions that form a metabolic pathway 2. Each reaction in a metabolic pathway is catalyzed by a specific enzyme 3. Metabolic pathways are similar in all organisms from bacteria to humans 4. Many metabolic pathways are compartmentalized in eukaryotes, with certain reactions occurring inside a specific organelle 5. Each metabolic pathway is regulated by key enzymes that can be inhibited or activated, thereby determining how fast the reactions will go. b. Cells trap free energy while metabolizing glucose i. The metabolism of glucose is a multistep process 1. Each step is catalyzed by an enzyme keeping it always under enzymatic control 2. The process is compartmentalized 3. The pathway is under enzymatic control ii. The dG of glucose and o2 to co2 and h2o is -686 kcal/mol iii. The metabolic processes 1. Glycolysis a. Produces three-carbon products- pyruvate from glucose b. Does not use O2 c. Small amounts of energy is produced by glucose 2. Cellular respiration (aerobic) a. Converts each pyruvate molecule into three co2 molecules through a set of metabolic pathways b. A great deal of the energy stored in the covalent bonds of pyruvate is released and transferred to create ATP 3. Fermentation (anaerobic)
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a. Converts pyruvate into lactic acid or ethyl alcohol (ethanol), which are still relatively energy-rich molecules. b. Because the breakdown of glucose is incomplete, much less energy is released by fermentation than by cellular respiration c. An overview: Harvesting energy from glucose i. The energy-harvesting processes in cells use different combinations of metabolic pathways depending on the presence or absence of O2. 1. When o2 is available as the final electron acceptor four pathways operate a. Glycolysis b. Pyruvate oxidation c. Citric acid cycle d. Etc 2. When o2 is unavailable a. Fermentation i. Produces lactic acid d. Redox reactions transfer electrons and energy i. The addition of a phosphate group to adp makes atp 1. Endergonic ii. Transfer of electrons transfers energy as well iii. This is done by a redox reaction 1. Reduction (lower charge ie: -2 to -3) a. Gain of one or more electrons by an atom 2. Oxidation (raise charge ie: -2 to 1) a. Loss of one or more electron. iv. Also think about the term in hydrogen atoms. 1. Moving an hydrogen means moving electron as well (H + and e - from H) v. When a molecule loses a hydrogen atom it becomes oxidized vi. Always occur together vii. Reactant that becomes reduced= oxidizing agent viii.Reactant that becomes oxidized= reducing agent e. The coenzyme NAD is a key electron carrier in redox reactions
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i. NAD is similar to atp
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This note was uploaded on 10/14/2009 for the course BIS 64982 taught by Professor Comai during the Spring '09 term at UC Davis.

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midterm 2 - Chapter 7: Pathways that harvest chemical...

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