Chapter 13: How Cells Obtain Energy From Food

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acetyl CoA

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small water-soluble molecule that carries acetyl groups in cells; contains an acetyl group linked to coenzyme A by an easily hydrolyzable thioester bond

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ADP

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nucleotide that is produced by hydrolysis of the terminal phosphate of ATP

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catabolism

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general term for the enzyme-catalyzed reactions in a cell by which complex molecules are degraded to simpler ones with release of energy

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citric acid cycle

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central metabolic pathway in all aerobic organisms that oxidizes acetyl groups derived from food molecules to carbon dioxide; in eucaryotic cells these reactions are located in the mitochondrial matrix

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electron-transport chain

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a series of membrane-embedded electron carrier molecules along which electrons move from a higher to a lower energy level, as in oxidative phosphorylation and photosynthesis

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FAD, FADH2

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a major electron carrier in metabolism produced by reduction during the oxidation of catabolites such as succinate

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fat

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lipids used by living cells to store metabolic energy; mainly composed of triacylglycerols

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fermentation

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the breakdown of organic molecules without the involvement of molecular oxygen; this form of oxidation is less complete than in aerobic processes and yields less energy

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GDP

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nucleotide that is produced by the hydrolysis of the terminal phosphate of GTP, a reaction that also produces inorganic phosphate; when free in solution, it is rapidly rephosphorylated to GTP, usually by the transfer of the terminal phosphate from ATP in the reaction ATP + GDP --> ADP + GTP

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glucose

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six-carbon sugar that plays a major role in the metabolism of living cells; stored in polymeric form as glycogen in animal cells and as starch in plant cells

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glycogen

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polysaccharide composed exclusively of glucose units used to store energy in animal cells; large granules are especially abundant in liver and muscle cells

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gluconeogenesis

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the synthesis of glucose from small organic molecules such as lactate, pyruvate, or amino acids

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glycolysis

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ubiquitous metabolic pathway in the cytosol in which sugars are incompletely degraded with production of ATP; literally "sugar splitting"

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NAD+, NADH

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activated carrier molecule that participates in an oxidation reaction by accepting a hydride ion from a donor molecule; widely used in the energy-producing breakdown of sugar molecules

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oxidative phosphorylation

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process in bacteria and mitochondria in which ATP formation is driven by the transfer of electrons from food molecules to molecular oxygen; involves the intermediate generation of a pH gradient across a membrane and chemiosmotic coupling

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pyruvate

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metabolite formed from the breakdown of glucose that provides a crucial link to the citric acid cycle and many biosynthetic pathways

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starch

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polysaccharide composed exclusively of glucose units, used as an energy store in plant cells

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ATP

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nucleoside triphosphate composed of adenine, ribose, and three phosphate groups that is the principal carrier of chemical energy in cells; the terminal phosphate groups are highly reactive in the sense that their hydrolysis, or transfer to another molecule, is accompanied by the release of a large amount of free energy

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GTP

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major nucleoside triphosphate used in the synthesis of RNA and in some energy-transfer reactions; also has a special role in microtubule assembly, protein synthesis, and cell signaling