Pyruvate possible fates

Pyrophosphate is rapidly hydrolyzed, and so the equivalent of four molecules of ATP are consumed in these reactions to synthesize one molecule of urea. The synthesis of fumarate by the urea cycle is important because it links the urea cycle and the citric acid cycle (Figure 23.17). Fumarate is hydrated to malate, which is in turn oxidized to oxaloacetate. Oxaloacetate has several possible fates (1) transamination to aspartate, (2) conversion into glucose by the gluconeogenic pathway, (3) condensation with acetyl CoA to form citrate, or (4) conversion into pyruvate. 

What are the possible fates of pyruvate in glycolysis In glycolysis, one molecule of glucose gives rise, after a long series of reactions, to two molecules of pyruvate. Along the way, two net molecules of ATP and NADH are produced. In aerobic metabolism, pyruvate is further oxidized to carbon dioxide and water. In anaerobic metabolism, the product is lactate or, in organisms capable of alcoholic fermentation, it is ethanol. 

Anaerobic glycolysis also occurs in micro-organisms that are capable of living in the absence of oxygen. Here there are two possible fates for the pyruvate formed from glucose, both of which involve the oxidation of NADH to NAD ... 

What are four possible fates of pyruvate in a mammalian cell ... 

FIGURE 14-3 Three possible catabolic fates of the pyruvate formed... 

In mammals, muscle breakdown or excess protein intake results in an imbalance between the fates of the carbon chains and the amino nitrogen. Unlike fat (lipid storage) or glycogen (carbohydrate storage), excess amino acids are not stored in polymeric form for later utilization. The carbon chains of amino acids are generally metabolized into tricarboxylic acid (TCA) cycle intermediates, although it is also possible to make ketone bodies such as acetoacetate from some. Conversion to TCA intermediates is easy to see in some instances. For example, alanine is directly transaminated to pyruvate. 

FIGURE 14-3 Three possible catabolic fates of the pyruvate formed in glycolysis. Pyruvate also serves as a precursor in many anabolic reactions, not shown here. 

Recall What are the possible metabolic fates of pyruvate ... 

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