Chapter 7 Study Guide - Study guide 7 UNIT II Cell...

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Study guide 7 UNIT II: - Cell Structure & Function - Respiration and Fermentation - Photosynthesis - Cell division Glycolysis and Fermentations Heterotrophic organisms get energy from free-energy-rich nutrients like carbohydrates , fats and proteins . Anaerobes do this by fermentation (glycolysis, in part), while the rest of us do it by respiration ( glycolysis , the Krebs cycle , electron transport/oxidative fermentation ). The free energy of nutrients is captured by ATP molecules ( Fig. 9.1 ), the energy currency of the cell (i.e., free energy for nearly all work a cell does is fueled directly by ATP. The free energy in ATP is in turn, used to fuel endergonic (free energy-requiring reactions) in cells such as the contraction of muscles, the movement of cilia and flagella, or even the polymerization of monomers into macromolecules. The hydrolysis of a phosphate from ATP is accompanied by the transfer of the phosphate to other molecules. In metabolic pathways, such phosphorylated molecules are “activated”, to undergo exrergonic reactions ( Fig. 9.3 ). In other examples, the phosphate is transferred to a protein, changing its shape and therefore its activity state ( Fig. 9.2 ). The free energy in nutrients is released when they are oxidized; this free energy is then captured in ATP molecules. Recall that pre-biotic redox reactions resulted in the reduction of inorganic and simple organic molecules, to make the free-energy rich nutrients of the primordial soup. Redox reactions involve the transfer of electrons: molecules that give up or lose electrons are oxidized while those that gain them are reduced ( Fig. 9.4 ). You can track the movement of electrons from glucose (a key energy nutrient) to oxygen in Fig. 9.5 . Organisms use the redox reactions of fermentation and respiration to get free energy from these nutrient molecules. As nutrient molecules or their intermediates are oxidized, electron carriers like NAD+ are reduced ( Fig. 9.7 ). Reduced electron carriers like NADH carry much of the free energy from nutrient oxidations; you can expect that this free energy will end up in ATP! The 4 steps of respiration evolved to take energy from nutrients, hold it in reduced electron carriers and finally put it into ATP, are summarized in Fig. 9.8 . . Because it can make ATP anaerobically (without oxygen), glycolysis may be the oldest biochemical (metabolic) pathway. As we will see, the other pathways (the Krebs cycle, electron transport, oxidative phosphorylation) evolved later as part of respiration , when levels of oxygen increased in the atmosphere.
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1. The glycolytic pathway takes place in the cytoplasm.
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