Adenosine triphosphate metabolic generation

Ethanol is a dietary fuel that is metabolized to acetate principally in the liver, with the generation ofNADH. The principal route for metabolism of ethanol is through hepatic alcohol dehydrogenases, which oxidize ethanol to acetaldehyde in the cytosol (Fig. 25.1). Acetaldehyde is further oxidized by acetaldehyde dehydrogenases to acetate, principally in mitochondria. Acetaldehyde, which is toxic, also may enter the blood. NADH produced by these reactions is used for adenosine triphosphate (ATP) generation through oxidative phosphorylation. Most of the acetate enters the blood and is taken up by skeletal muscles and other tissues, where it is activated to acetyl CoA and is oxidized in the TCA cycle. 

Adenosine triphosphate (ATP) The principal chemical energy source for cellular processes. It is largely produced during aerobic metabolism. In the neuron most ATP is used in the maintenance of the electrochemical gradient required to generate an action potential. 

Microbial activity requires energy, and all microorganisms generate energy. This energy is subsequently stored as adenosine triphosphate (ATP), which can then be utilized for growth and metabolism as needed, subject to the second law of thermodynamics [2,23,35,41,42,51,54]. 

When fuels are metabolized in the body, heat is generated and ATP (adenosine triphosphate) is synthesized. 

The Krebs cycle is a series of enzymatic reactions that catalyzes the aerobic metabolism of fuel molecules to carbon dioxide and water, thereby generating energy for the production of adenosine triphosphate (ATP) molecules. The Krebs cycle is so named because much of its elucidation was the work of the British biochemist Hans Krebs. Many types of fuel molecules can be drawn into and utilized by the cycle, including acetyl coenzyme A (acetyl CoA), derived from glycolysis or fatty acid oxidation. Some amino acids are metabolized via the enzymatic reactions of the Krebs cycle. In eukaryotic cells, all but one of the enzymes catalyzing the reactions of the Krebs cycle are found in the mitochondrial matrixes. 

The major pathway by which P enters into organic combination in plants is through formation of adenosine triphosphate (ATP) (Chapter 11.3). The latter is generated during photosynthesis, and is required by numerous metabolic processes. Among these are the assimilation of N and S by the plant, the transport of various nutritional ions through cell membranes, and the production of plant starch and cellulose (Table 12.7). 

In addition to these we need to mention a small group of metabolites that belong structurally with the building blocks of nucleic acids but which have major metabolic functions that are quite separate from their relationship to nucleic acids. These are the adenosine phosphates two of these, adenosine 5 -triphosphate and adenosine 5 -diphosphate, participate in many metabolic reactions (more, indeed, than any other substance, aside from water) a third, adenosine 5 -monophosphate, participates in relatively few reactions but affects many enzymes as an inhibitor or as an activator. These names are cumbersome for everyday use and biochemists refer to them nearly aU of the time as ATP, ADP, and AMP, respectively. In animals, the ATP needed for driving all the functions of the cell is generated in small compartments of cells called mitochondria. For the purposes of this book we shall not need to know any details of how mitochondria fulfill their functions, but we do need to know that they exist, because we shall meet them again in a quite different context it turns out that in most organisms mitochondria contain small amounts of their own DNA, and this allows some special kinds of analyses. Adenosine, the skeleton from which ATP, ADP, and AMP are built, has a separate importance as one of the four bases that define the sequence of DNA. 

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