Chapter%2017%20-%20Metabolism%20%28overview%29-1

Chapter%2017%20-%20Metabolism%20%28overview%29-1 -...

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Metabolism – an overview Essential Question What are the anabolic and catabolic processes that satisfy the metabolic needs of the cell?
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1. Maximize the efficiency of fuel utilization by preventing the simultaneous operation of opposing pathways (i.e., futile cycles). 2. Partition metabolites appropriately between alternative pathways. 3. Draw on the fuel best suited for the immediate needs of the organism. 4. Shut down biosynthetic pathways when their products accumulate. Principles of metabolic regulation There are four major principles that have selectively evolved throughout evolution:
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Metabolism in Different Organisms Organisms show remarkable similarity in their major metabolic pathways This is evidence that all life descended from a common ancestral form And yet, living things also exhibit metabolic diversity Oxygen is essential for aerobes, but obligate anaerobes are poisoned by oxygen The flow of energy in the biosphere and the carbon and oxygen cycles are intimately related The impetus driving the cycle is light energy
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Diversity of Metabolism in Different Organisms Autotrophs use CO 2 Heterotrophs use organic carbon Phototrophs use light Chemotrophs use organic and inorganic electron donors
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The Sun is Energy for Life Phototrophs use light to drive synthesis of organic molecules Heterotrophs use these as building blocks CO 2 , O 2 , and H 2 O are recycled The flow of energy in the biosphere is coupled to the carbon and oxygen cycles
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Metabolic Maps Metabolism consists of catabolism and anabolism Catabolism: degradative pathways Usually energy-yielding Anabolism: biosynthetic pathways Usually energy-requiring Metabolic maps portray the principal reactions of intermediary metabolism; More than 500 different chemical intermediates, or metabolites, and a greater number of enzymes are represented here. When the major metabolic routes are know and functions are understood, the maps become easy to follow, in spite of their complexity
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Metabolic Maps One interesting transformation of the metabolic map represents each intermediate as a black dot and each enzyme as a line In this way, more than a thousand enzymes and substrates are represented by just two symbols A dot connected to a single line must be a nutrient, a storage form, an end product, or an excretory product A dot connected to just two lines is probably an intermediate in one pathway and has only one fate in metabolism A dot connected to three represents an intermediate that has two metabolic fates Figure 17.3 The metabolic map as a set of dots and lines. The heavy dots and lines trace the central energy-releasing pathways known as glycolysis and the citric acid cycle.
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Chapter%2017%20-%20Metabolism%20%28overview%29-1 -...

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