Discuss the fate of pyruvate.

ANSWER: The product of glycolysispyruvateis a versatile metabolite that can be used in several ways. In most tissues, when oxygen is plentiful (aerobic conditions), pyruvate is oxidized (with loss of the carboxyl group as CO2), and the remaining two-carbon unit becomes the acetyl group of acetyl-coenzyme A (acetyl-CoA). This acetyl group is metabolized in the tricarboxylic acid (TCA) cycle (and fully oxidized) to yield CO2. Alternatively, in the absence of oxygen (anaerobic conditions), pyruvate can be reduced to lactate through oxidation of NADH to NAD+a process termed lactic acid fermentation. In microorganisms such as brewer's yeast and in certain plant tissues, pyruvate can be reduced to ethanol, again with oxidation of NADH to NAD+ in a process called alcoholic fermentation.