Adenosine triphosphate fuel metabolism

Cell respiration describes the metabolic reactions and processes that occur in a cell to produce energy in the form of adenosine triphosphate (ATP) from fuel molecules and the... 

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. 

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. 

The coenzyme adenosine triphosphate (ATP) acts as the central link between energy-yielding metabolic pathways and energy expenditure on physical and chemical work. The oxidation of metabolic fuels is linked to the phosphorylation of adenosine diphosphate (ADP) to adenosine triphosphate (ATP), while the expenditure of metabolic energy for the synthesis of body constituents, transport of compounds across cell membranes and the contraction of muscle results overall in the hydrolysis of ATP to yield ADP and phosphate ions. The total body content of ATP + ADP is under 350 mmol (about 10 g), but the amount of ATP synthesized and used each day is about 100 mol — about 70 kg, an amount equal to body weight. 

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